Proceedings of the international conferences on the bearing capacity of roads, railways and airfields

Introduction to the conference

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What Does an Aircraft Expect From the Pavement?

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Modern Railways for Cargo and Passenger Traffic High Speed- Heavy Loads Track Systems

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The paper discusses the major component s of railway superstructure systems, their dimensioning, and their role in guaranteeing a safe and efficient transportation of passengers and goods.

Impact of Heavy Vehicles on European Roads

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More then 500 billion € is spent yearly in the European Union on mobility. The road traffic is increasing at a rate of four to five percent each year, leading to an expected growth from mow to the year 2020 of fifty to sixty percent. The road network is extremely important to Europe’s economic and it requires efficient management using state of the art technology. The traffic volume of heavy vehicles using the road network has been increasing steadily over the last decades, as is the trend for increasing individual axle loads. The weighing of road vehicle axles in motion (WIM) is getting more and more an important factor for the record and analysis of the traffic stream. One chapter of this paper describes new applications of a special method SIM (stress in motion) for the measurement of force distributions under rolling wheels.

Comparative Study of Laboratory Based Methodologies for Determination of the Resilient Performance of Clay Subgrades

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For the development of performance-based design for pavement foundations appropriate laboratory assessment of the underlying subgrade is required. To achieve this, assessment of the resilient behaviour (stiffness) and resistance to permanent deformation of the subgrade must be made, under realistic loading conditions. This paper compares data from variably confined repeated load tests (utilising the recently developed “Springbox” apparatus), simplified repeated load triaxial tests (using standard triaxial apparatus) and repeated load triaxial tests. Tests were undertaken on a series of remoulded clay subgrade materials for a range of water contents prepared between the plastic limit and a predicted long-term equilibrium value. Correlations of the resilient deformation (stiffness) measured in the various tests are presented, together with comments on their applicability for pavement design. Having accommodated the differences in the confining stress, acceptable comparisons
between the data from the various devices are achieved. However, the quality of the resilient data from the simplified procedures was affected by the resolution of instrumentation, producing better correlations at higher applied stresses where the stiffness approaches a constant value termed the “stiffness asymptote”. A correlation between stiffness asymptote and sample plasticity is also presented. To conclude, the suitability of the various test devices is discussed and outstanding design/sample preparation issues considered. Significantly this includes the need to predict and manufacture samples representative of long term (equilibrium) subgrade water contents.

Strong Correlation between the Bearing Capacity and CBR of a Gypsiferous Subgrade Soil Subjected to Long-Term Soaking

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Presented in this paper is a correlation between the bearing capacity of a gypsiferous subgrade soil with the corresponding CBR value. The geotechnical tests carried out on this soil indicate that the soil is sandy lean clay of CL group according to the USCS and A-6 (6) group according to AASHTO Soil Classification System. The soil contains about 33% gypsum content. For this purpose, thirty six CBR samples were prepared at optimum moisture content (of the modified AASHTO compaction test) namely 11.5% at compactive efforts of 1, 2 and 4.56 times that of the Proctor compaction (standard AASHTO). These
samples were soaked for 0, 4, 7, 15, 30, and 120 days under the effect of 40 lbs (178 N) surcharge load. For each soaking period, three pairs of CBR soil samples were prepared, one for each compactive effort. The first CBR sample from each pair was used to determine the CBR value while the second CBR sample was used to obtain triaxial soil samples for unconsolidated undrained tests to arrive at the corresponding shear strength parameters. The present paper reveals that for each soaking period, there is a linear increase of the ultimate bearing capacity with increasing compactive effort, while a significant drop in the ultimate bearing capacity of the tested soil took place with increasing soaking period. The paper
reveals also that there is a strong linear correlation between the estimated ultimate bearing capacity and the corresponding CBR value indicating that the Rosenak's equation correlating the bearing capacity with CBR value is very conservative.

Prediction of stiffness of unbound granular materials based on the CBR value

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The unbound granular materials (UGM), base and subbase layers, play an essential role in the overall structural performance of thin pavement structures. They show complex stress dependent elasto-plastic behaviour under external loading. Therefore the UGM are commonly tested using the Repeated Load Triaxial (RLT) testing method to estimate the stiffness of the material by applying haversine loading pulses. The RLT testing method
represents the actual stress situation quite adequately and gives satisfactorily estimates of the stiffness characteristics of UGM. However a RLT test is an elaborated test and rather expansive. A much simpler test that has been used for a long time in structural design of flexible pavements is the CBR (California Bearing Ratio) test. The CBR test is a simple and cheap test where the load-deformation curve is acquired while a plunger is penetrated into the material at a constant rate. In the literature one can find a number of relationships for UGM
where the CBR value is used to predict the stiffness. To investigate if a connection between the two tests exists, twenty materials have been tested with both methods and the test results compared. The materials were of varying quality but all were fairly well graded. The results indicate that a simple power law can be used to predict the stiffness if the CBR-value is known.

Influence of Degree of Saturation on Bearing Capacity and Compaction of Glacial Till Embankments

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In Sweden the consumption of aggregate each year equates to eight tons per capita and is responsible for half of all goods transportation in Sweden. Approximately 20
million tons of aggregate material is transported to different road construction sites each year. With a more balanced and active design code site-won materials could be utilised as an
alternative to imported rock fill. This would not only reduce transportation costs but also minimise impact on the environment. This paper explores the possibility of utilising site-won
glacial till in road pavement construction above the current permitted level of capping layer level. The bearing capacity of glacial till at three different sites is investigated with
corresponding laboratory tests on compaction properties, since compaction is a crucial factor in the bearing capacity obtained. Results are compared with the criteria specified in the
Swedish design code for each structural road layer. It will be shown that a fill with moderate fines content, compacted close to its optimum water content, meets the requirements for a
sub-base material on bearing capacity. This is due to the influence of negative pore pressure and its positive impact on shear strength. Certain areas of uncertainty remain such as frost
susceptibility and the effects of seasonal variation on degree of saturation beneath a paved construction and should be tackled in the future. To enable future implementation of tills in
structural road layers a new approach to managing fills on site is required which covers crucial issues such as weather conditions and timing of the construction works.

A study on the influence of water and fines on the deformation properties of unbound aggregates

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To achieve proper stability in base coarse materials, there is a variety of parameters to optimize. The response of the material is a combination of several factors, such as grading, water content, material strength, stress level etc. It is well known that the grading of a material is important for the stability and that a well graded material normally gives better stability than a
single sized or a less graded material. In the Norwegian guidelines for pavement design there are restrictions to ensure that the fines content is under a certain level to ensure a none-water susceptible material and hence avoid loss of bearing capacity during spring thaw. In this study the main focus is to study how the deformation properties, elastic as well as
permanent deformation behavior, are affected by different combinations of water content, grading and material strength. The grading of the material is based on the gradation curves for base course material in the Norwegian guidelines for pavement design, which is based on the fuller curve. Cyclic triaxial tests have been used to study the material behaviour in the laboratory.

Influence of Suction on the Properties of two Granular Road Materials

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The results of an experimental work on two road granular materials are presented, including small strains precision triaxial tests under cyclic loading, large strains triaxial tests with measurement of the negative pore water pressure (suction) and wetting tests. The influence of different initial conditions of density, water content and fines content was studied. The two materials differ by their fine contents (7 % for MHC and 10% for HFC). The specimens are compacted at different water content and at a density corresponding to 97% of the Modified Proctor
maximum density. The interpretation of the results, in the quasi-elastic domain, is based on an effective stress analysis that allows to take into account both the effects of total stresses and negative pressure, in the perspective of a more rational design of pavement layers.

A new material model for permanent deformations in pavements

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Today's demand in pavement design for a calculation method to evaluate rutting (permanent deformations) is wide and global. The new procurement methods together with functional requirements are underlining this rutting evaluation demand in different pavement materials and layers. Permanent deformation research has become more general during the last decade. VTT (the Technical Research Centre of Finland) has researched many different aspects of permanent deformations with accelerated pavement tests. Accelerated pavement tests have been conducted with the Heavy Vehicle Simulator (HVS-Nordic). The HVS tests have been completed with a wide triaxial test programme in laboratory. The HVS tests have shown that it is difficult to predict in advance where in the pavement rutting happens: in the subgrade or in the structural layers. A new material model based on the laboratory and HVS tests has been developed in VTT. The objective was to develop a material model for unbound materials, which is an analytical, nonlinear elasto-plastic model. The stress distribution studies of traffic load have shown that it was very important to calculate stresses in pavements with an elasto-plastic material model to avoid tensile stresses in unbound materials, especially when the asphalt layers were thin. The new material deformation model can take into account the number of the passes, the capacity
of the material and its stress state. The deformations in each layer are calculated and then summed together to obtain the total rutting on the surface of the structure.

A Laboratory Measurement of The Hydraulic Conductivity of Fragmented Gravels

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Due to severe environmental conditions and the action of different type of loading forces, granular materials that form the base of a road pavement may be subjected to crushing and fragmentation. The effect of the small fragments that move into the voids as a result of crushing is that they may have increased the bearing capacity of the base material. However, when the volume of the voids is decreased due to the migration, the flow ability of the material is said to reduce. This change in the engineering property of the material may lead to an undesirable drainage pattern within the pavement. A number of laboratory tests were conducted and repeated whereby small gravels were gradually fragmented and the hydraulic conductivity of the materials were measured. In this study, the pattern of fragmentation of different gravels was analyzed using fractal theory and the hydraulic conductivity of the gravels before and after different stages of fragmentation were measured. From the measurement of fractal dimension number in the fragmented rock it was found that as the fractal dimension is increased the hydraulic conductivity of the material is decreased.

The Routine Laboratory Assessment of the Performance of Coarse Granular Materials for Pavement Foundation Design

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A performance based specification for road foundations potentially allows any material that can be assessed as ‘fit for purpose’ to be used, and encourages the wider use of marginal and recycled/secondary materials. For such a specification to be implemented information of material stiffness and resistance to permanent deformation is required for analytical design, and tests must be available to validate the design parameters onsite. Therefore a routine, economical laboratory-scale test needs to be developed to assess the performance and suitability of any poten tial foundation material to provide data for design, and ideally such a test should link to the field-based compliance testing. To facilitate this a large-scale laboratory test has been developed to assess the performance of coarse granular materials, typical of those used in UK pavement foundations. The test utilises a heavy duty steel box with a synthetic base layer, and portable test devices. This paper evaluates the performance of the test by comparing the results from a compacted sample of a typical site won “capping” material to associated field data. To validate the test methodology analysis of the stiffness test data for each layer compacted within the tests sample is presented. The effects of a soft and rigid base condition, and wetting and drying of the material is shown to have a significant effect on the measured values of both stiffness and strength. However, there appears a reasonable relationship between the laboratory results for the soft base condition and the field data.

Prediction of permanent deformations of unbound pavement layers

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This paper presents a simplified method for modelling of permanent deformations of unbound granular pavement layers, using finite element calculations. This method is based on a model of prediction of permanent deformations of unbound granular materials, developped from repeated load triaxial testing [Gidel, 2001]. The permanent deformations in the pavement structure are calculated in two steps : The first step consists in modelling the resilient behaviour, using non linear elastic models, to determine the stress field in the pavement. The second step consists in using the stress paths obtained at different points in the pavement structure to calculate the permanent strains, using the permanent deformation model. The approach is used to predict the rutting of a low traffic pavement structure, with unbound granular base, tested on the LCPC accelerated testing facility.

Advanced Models for Predicting Aggregate Rutting Behavior

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Artificial neural network (ANN) based advanced aggregate rutting models have been developed and compared for performance using laboratory test data. The primary goal has been to properly characterize the loading stress path dependent permanent deformation behavior from advanced repeated load triaxial tests that can simulate in the laboratory the varying stress states under actual moving wheel load conditions. The aggregate specimens tested were the Federal Aviation Administration (FAA) specified P209 base and P154 subbase materials also used in the pavement test sections of the FAA’s National Airport Pavement Test Facility (NAPTF). Due to the complex loading regimes followed in the laboratory tests and the full-scale NAPTF testing, the ANN rutting models that altogether considered as inputs the static and dynamic components of the applied stresses and the loading stress path slope produced the greatest accuracy. Such advanced neural network models can better describe the aggregate rutting behavior under actual field loading conditions.

Evaluation of grain shape characterization methods for unbound aggregates

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A laboratory study is performed on an unbound aggregate of gneiss commonly used as base course in road pavements. Aggregate samples with four different grain shapes from the same quarry have been tested. The objective of this study was to evaluate different methods of grain shape characterization to see which methods that gives the most reliable results for the same materials on the parameters describing shape, angularity and surface texture. One group of methods for grain shape characterization is simple petrologic methods in combination with physical measurements of the aggregate shape. These methods are based on visual classifications of rock type and measurement of the aggregate dimensions giving several shape characteristics as flatness and elongation ratio, angularity, degree of sphericity, flakiness index, shape index etc. The most common test in this group is the flakiness index test. Image analyses are more sophisticated in their characterization of the aggregate shape. These methods are also more powerful in their ability to characterize surface roughness. Two
dimensional analysis give a picture of each grain in only two dimensions, i.e. the projection of the grain on one plane in a random position. The most advanced methods are the three
dimensional image analysis.

Evaluation of the effect of particle shape on the bearing capacity of railroad ballast with discontinuous analysis

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This paper examines the effects of particle properties such as particle shape and grain size distribution of particle assemblage on the bearing capacity of railroad ballast in numerical simulations with discontinuous analysis. To evaluate the effect quantitatively, a se-ries of numerical simulations that regard a ballast particle as a regular or an irregular polygon were performed. By comparing model tests of ballasted track with the numerical simulations, the validity of modeling methods of railroad ballast in discontinuous analysis was examined in terms of the shape of ballast particles and the grain size distribution of railroad ballast. As the result, it can be observed that the particle shape of numerical models, especially the angu-larity has a greater effect on the bearing capacity of railroad ballast than the grain size distri-bution, and that the imitation of the shape of real ballast particles makes analytical results similar to experimental results.

Round robin investigation on the cyclic triaxial test for unbound granular materials

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A new European standard for cyclic triaxial testing of unbound granular materials was approved by CEN in 2004. In the final stages of preparation of the standard it was decided to organize a round robin analysis with invitation to laboratories in Europe that have been doing research using this type of tests. Nine different laboratories received the material and six laboratories performed the tests. Only one material at one target dry density and water content was investigated. Most of the laboratories performed three parallel tests. This is obviously too few tests for a statistically sound validation of the tests. However, some indication about the accuracy of the test was found.

Characterisation of Some Candidate Surfacing Materials for Orthotropic Steel Bridge Decks

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To study the distress phenomena of orthotropic steel deck bridges, and in particular the rather short lifespans of surfacing materials, a research project has started at the Technical University of Delft. The main goal of the research is to suggest new design techniques for the structure. To achieve this goal, it is important to characterise some candidate surfacing materials for orthotropic steel deck bridges. In this paper, results of an extensive experimental program on three surfacing materials will be presented. The mixes which were tested in this program are: SBS modified mastic asphalt, guss asphalt and open synthetic wearing course. The tests carried out included: fatigue tests, frequency sweep tests, uniaxial monotonic compression and tension tests and static indirect tensile tests. Several properties/phenomena have been quantified and modeled e.g. dependency of mix stiffness on strain levels, dependency of compressive/tensile strength on temperature and strain rate.

Linear viscoelastic properties of mastics: results from a new annular shearing rheometer, and modelling.

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The mastic, composed of bitumen and filler, is an intermediate material between bitumen and mix. It can be considered as the real binder in the mix. Measuring its mechanical behaviour will contribute to closing a gap when linking binder and mixture properties. A new specifically designed annular shearing rheometer was developed at the DGCB laboratory (ENTPE) to study bituminous mastics. The complex modulus G* of mastics is measured in a large range of temperatures (-25°C to 70°C) and frequencies (0.03 to 10 Hz). The samples tested are larger than those currently tested (hollow cylinder: external diameter = 105 mm, thickness = 5 mm, height = 40 mm). An experimental campaign on the linear viscoelastic behaviour of different bituminous mastics was carried out at low strain level. The aim was to determine the effect of i) the filler size, ii) the filler concentration, and iii) the grading of the filler, iv) the filler type on the complex modulus of the materials.
A part of the analyses of the complex modulus data is proposed. A significant difference in behaviour between mastics and bitumen is observed: a decrease of the phase angle (complex modulus) of mastics at high temperatures is probably linked to the existence of contacts between filler particles. A unique rheological model (2S2P1D) developed at DGCB is used to model the experimental results. A function of the filler concentration is considered to describe the continuous change in properties from bitumen to mastic.

Computational Fluid Dynamic Modelling of the Rotational Viscometer

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The use of fillers in a bituminous binder satisfies two main criteria: the improvement of the system’s mechanical properties and the utilisation of waste products with the associated environmental benefit. An increasing number of filler materials are being used, all with different gradations and specific gravities. It is important to the asphalt technologist to understand the effect the fillers have on the viscosity of the hot bitumen and to ensure even distribution of the filler particles within the mix. One of the instruments used to quantify the behaviour of hot bitumen and bitumen-filler mixtures is the rotational viscometer. Previous research has identified substantial changes in the viscosity with time of both the pure bitumen and the bitumen-filler mixture when measured by the rotational viscometer.
This study uses Computational Fluid Dynamics (CFD) to model behaviour of the bitumen and bitumen-filler in the viscometer. By means of complex rheological models, the pseudoplastic and thixotropic nature of the bitumen is identified and successfully modelled. In addition, the effect of filler drift is identified and modelled, indicating that the steady state equations used to calculate viscosity in the viscometer are invalid for such systems.

Comparison of the Zero Shear Viscosity of Bitumen-Filler Mastics Using Different Measurement Techniques

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Zero shear viscosity (ZSV) or the viscosity at zero shear rate is an intrinsic property of a bituminous binder that has been proved to have a good correlation to the rutting potential of most binders, particularly modified binders. Various techniques and procedures exist to calculate or estimate ZSV. These include creep flow with or without creep recovery, viscosity measurements at low shear rates, sinusoidal oscillation at low frequencies and repeated creep (pulsed creep). Most of these techniques are performed on a dynamic shear rheometer with the ZSV being determined directly from the plotted data or, particularly in the case of the oscillation test, extrapolated to zero frequency using an appropriate mathematical model. This paper investigates the effect of modifying a bituminous binder through the addition of filler to produce bitumen-filler mastic similar to that found within an actual asphalt mixture. The ZSVs of bitumen-filler mastics with different filler types and bitumenfiller ratios have been tested. Three types of filler have been included in the testing programme including inert fillers (limestone and gritstone) as well as an active filler (cement) at various filler-bitumen ratios ranging from 15% to 65%. The ZSV results show varying degrees of modification (increases) of ZSV as a function not only of filler content but also of filler type. In addition, the ZSVs determined by means of the different procedures gave statistically different values, again as a function of both filler content and filler type.

The New Method of Evaluation of Stress Relaxation Properties in Road Bitumens

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Methods of evaluation of bitumens’ functional properties according to SHRP (Strategic Highway Research Program) and Qualagon (Shell’s method) nowadays widely presented in literature, beside their advantages, have also some faults due to their labourconsuming ness, expensive equipment and limited universality which doesn’t include evaluating of polymer modified bitumens. However fundamental disadvantage of methods stated above is disregarding evaluating of bitumens’ ability to dissipating stresses (internal energy) which accumulate in binder due to effect of forces and external loads.
Taking into consideration limitations stated above, authors took effort to elaborate method of evaluate stress relaxation velocity in given temperature. The principle of method is to measure cohesion of binder sticking together two polished mineral plates at two shear speeds in constant temperature. Cohesion was determined by means of the direct shear apparatus with the adjustable shearing speed. In this research were used three kinds of bitumens with
approximate hardness but with different chemical composition. To determine the binder cohesion tile-like limestone samples were used. Thickness of bitumen film sticking those plates was chosen to minimize influence of mineral surface on cohesion’s results of examined bitumens. Obtained cohesion values (at constant temperature) enable to estimate bitumen’s susceptibility to dissipate stresses according to its chemical quality and hardness.

Evaluation of a newly developed asphalt binder selection system for mix design

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A Norwegian research project (PROKAS) has been conducted in the period 1998 – 2004. One objective was to develop performance-based specifications for Norwegian asphalt mixtures. As a part of this project a new binder selection system was sketched (Andersen, 2000). This system was based on results from the Norwegian research project New Asphalt technology, a project aiming at adaption of the Superpave binder system to Norwegian conditions. An attempt to verify this binder selection system in the laboratory has been made. Deformation properties of asphalt mixtures with different binder stiffnesses have been measured (Lerfald, 2004). The same aggregates and material gradings were used in all samples. The new asphalt binder selection system shows relatively good correlation with results from the deformation tests. However, further testing with other mixtures and higher temperatures will be required to fine-tune and fully verify the system.

The Effect of Aging on the Rheology and Fatigue Response of Bitumen in Relation to Raveling in Porous Asphalt

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Due to ever increasing traffic loading, the need for long lasting pavements is growing. At the same time the demand for quieter roads is also becoming crucial in the Netherlands with its dense population. Porous asphalt (PA) is extensively used as surface layer on motorways in order to reduce traffic induced noise. However, the durability of PA layers is relatively low because of the high voids content in the mix. In this study, the effect of aging on the binder performance was investigated. The rheological investigation revealed that increase in modulus is achieved in the high (low frequency) and intermediate temperatures while no significant change is achieved at low temperatures. The fatigue response of the binder to repeated application of shear loading at intermediate temperatures using the time-sweep test in Dynamic Shear Rheometer (DSR) showed higher rate of damage development in aged binders but the performance was better than the unaged bitumen according to the evaluation made using fatigue resistance parameter Np. Initial test results thus ascertained the need for low temperature binder performance as a most relevant and critical factor for characterizing binder performance in relation to raveling / durability problem in PA.

Characterisation of Uniaxial Creep Deformation Behaviour of Asphalt Mixtures

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Compressive uniaxial creep and creep recovery tests have been conducted on two generic UK asphalt mixtures over a range of temperatures and stress levels. Instantaneous elastic, viscoelastic (delayed elastic) and viscoplastic behaviour have been observed and volumetric changes have been studied. The elastic modulus of the DBM was found to be greater than that of the HRA. The viscoelastic strain was found to increase approximately in proportion to the total stain up to a certain point, above which it tends towards a constant level. The steady state viscoplastic deformation behaviour of the mixtures was found to be nonlinear with exponents of 2.5 and 5.4 for the HRA for the DBM respectively. Both mixtures were found to dilate under creep loading with more dilation exhibited by the DBM mixture due to increased aggregate interlock. The dilation ratio was found to be independent of stress level and dependent on the type of mixture and test temperature.

A contribution to the modeling of permanent deformations of bituminous mixes

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Rutting is one of the well-recognized road surface distresses in asphalt concrete pavements that can affect the pavement service life and traffic safety. The rutting phenomenon is linked with the permanent deformation accumulated after each cyclic loading due to the traffic. It is rather badly described by the traditional pavement analysis method. No rational approach is proposed to model this effect. A new test was developed at the “Département Génie Civil et Bâtiment” (DGCB) of the “Ecole Nationale des Travaux Publics de l’Etat” (ENTPE) to study permanent deformation of bituminous mixes. Experimental tests were carried out in order to contribute with the comprehension of the phenomena and the formulation of a law adapted for the rutting phenomenon modeling.A thermo-viscoplastic law has been developed at the DGCB for bituminous mixes during the last decade. This law introduces various experimental observations: general linear viscoelastic behaviour in the small strain range, non-linearity and viscoplastic flow. The aim of this paper is to widen the scope of this law by introducing permanent deformation in his formalism. Comparisons between the experimental value and the computed value of the slope of the secondary stage are presented for three temperatures (15°C, 25°C and 35°C), two frequencies (1Hz and 10Hz), and five stress amplitudes (0.1MPa, 0.2MPa and 0.3MPa in compression and –0.05 and –0.1MPa in extension).

Asphalt Cold Mixtures for Pavement Rehabilitation: Curing and Mechanical Characteristics

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This paper presents the main results achieved in a research study concerning pavement rehabilitation using asphalt cold mixtures, specifically the application of “new” asphalt cold mixtures as overlays and in situ cold recycling of existing pavement layers with bitumen emulsion. In the frame of this research project, a study was performed comprising the haracterization of the materials used in the production of selected cold mixtures (both “new” materials and old materials used for recycling), and the mixtures produced. Studies were
performed about the most appropriate methods for representation of the in situ conditions in the laboratory. Furthermore, the effects of the curing process in the mechanical behaviour of the bituminous mixtures were also studied through laboratory testing. A comprehensive laboratory test programme was established, with the purpose of assessing the mechanical
characteristics of dense graded asphalt cold mixtures, especially those related to pavement performance.

Characterisation of Fatigue Damage of Asphaltic Materials

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Four-point bending fatigue tests were conducted on asphalt specimens under controlled strain and stress to study damage evolution using the stiffness modulus. A common feature in these tests, irrespective of mode, was that modulus eterioration could be split into three phases; initial (rapid deterioration), intermediate and final in which failure occurred. Damage was modelled based on behaviour at the intermediate phase during which the modulus appeared to follow a straight-line v number of cycles. The effect of test mode on fatigue behaviour was facilitated by the inclusion in the model of a dissipated energy parameter, measured over the intermediate modulus evolution phase. A simple iterative approach was adopted in the model to produce a unique damage parameter that describes the material’s fatigue performance independent of test mode. The damage concept was applied to two asphalt mixtures; a stone mastic asphalt (SMA) used as surfacing on major roads and a dense bitumen macadam (DBM) used as binder course on lightly trafficked roads. The effect of binder modification on resistance to fatigue damage was also included in the study. The SMA binder was modified by the addition of different quantities of crumb rubber modifier (CRM) obtained from truck tyres to study the effect of CRM content. The DBM binder was modified by the addition of CRM from truck and car-tyres to study the effect of CRM origin. When plotted v initial strain, the deduced damage parameter showed a clear distinction in ranking the mixtures in accordance with their fatigue performance.

Prediction of thermal cracking resistance of some SBS modified binders and mixes

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The most recent addition to bituminous binder low-temperature specification in the US is AASHTO MP1a standard which uses a thermo-visco-elastic model to calculate induced thermal stress using binder creep compliance (determined from the Bending Beam Rheometer) and the empirical “Pavement Constant” 18. The predicted thermal stress curve is compared with binder tensile strength data obtained from the Direct Tension Test to determine a “critical cracking temperature” (Tcr) below which thermal cracking occurs. This
paper presents an approach, both alternative and rational, to predict the thermal cracking resistance of bituminous materials. The complex modulus and DTT tests were respectively used, at the APPIA laboratory, to investigate the linear viscoelastic and failure properties of different SBS modified binders (with or without cross-linking). A recent method, introduced by Olard & Di Benedetto in 2003, was used to predict the mix complex modulus from the binder one so that the empirical Pavement Constant 18 is not needed in the binder specification anymore. The thermal stress was then calculated using the mix complex modulus properties predicted from those of the binders. The mix tensile strength was supposed to be close to that of the binder in the brittle domain. This experimental campaign and the proposed numerical analysis was performed to develop a handy tool for predicting the thermal cracking resistance of bituminous materials as an alternative to the current Superpave specification. Eventually, some restrained cooling tests confirmed the efficiency of the proposed new methodology.

Evaluation of Indentation Test to Characterize Asphalt Concrete Mixtures in Pavements

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The primary material property for characterizing asphalt concrete in the USA is the dynamic complex modulus. However, the dynamic complex modulus test is expensive and time consuming, making it impractical for use as a quality control test in the field. Therefore, there is a need for a test which can characterize asphalt concrete mixtures and can be performed, relatively simply, in the field immediately after construction. In the present study, the indentation test, which measures deflection under a constant load, was investigated for this purpose. Three replicates of the following four mixtures, having a nominal aggregate size of 12.5 mm and a PG64-22 binder, were fabricated and tested at 60ºC: 3.7% asphalt content and 4% air voids; 3.7% asphalt content and 7% air voids; 4.2% asphalt content and 4% air voids; and 4.2% asphalt content and 7% air voids. Air voids and asphalt content were varied since these are the volumetric parameters which are most likely to vary in the field and at the plant, respectively, and which have the greatest influence on pavement performance. The shear compliance obtained from the indentation test was found to be repeatable and sensitive to a change in air voids. However, the results do not seem to show a significant sensitivity to asphalt content, which is believed to be due to the localized nature of the indentation test. These results suggest that the indentation test may have limited applicability as a quality control and quality acceptance test in the field.

Evaluation of Test Data Variability and Suitability of Predictive Equation Related to the Determination of Dynamic Modulus (E*) for Hot-Mix Asphalt

2019-08-03T09:29:11+00:00

The dynamic modulus (|E*|) of hot-mix asphalt (HMA) is one of the fundamental inputs in the mechanistic-empirical (M-E) Design Guide developed in NCHRP Project 1-37A. The M-E Design Guide provides three levels for |E*| inputs, which depend on the importance of the pavement in service. Level 1 |E*| inputs require laboratory measured |E*| values while level 2 and 3 |E*| inputs are estimated using a predictive equation. To provide the laboratory measured |E*| inputs for implementation of the M-E Design Guide, a significant |E*| testing program was completed in Arkansas. The testing program included three replicate specimens from each of four aggregate types, three nominal maximum aggregate sizes, two PG binder grades, and two air-void levels. The |E*| tests were conducted using five test temperatures and six loading frequencies. The |E*| values obtained in this testing program exhibited much lower variability than those in other studies and complied with the required variability level specified in AASHTO TP 62-03. Therefore, the laboratory measured |E*| values can be used with confidence for level 1 material characterization inputs for HMA in the M-E Design Guide. Level 2 and 3 |E*| inputs, estimated using the predictive model provided sufficiently accurate predictions of pavement performance compared to performance predictions generated by the Level 1 inputs . In addition, the differences between level 2 and 3 predicted distresses were not significant. Thus, level 3 |E*| inputs could be used with confidence for initial implementation of the M-E Design Guide.

Evaluation of Temperature Associated Cracking in Asphalt Mixtures by Means of Performance-Based Laboratory Testing

2019-08-03T09:29:11+00:00

In this paper, new test methods for identification of low-temperature failure of asphalt are proposed. Low-temperature failure occurs when the stresses induced by restrained thermal shrinkage during cooling periods exceeds the tensile strength at the respective temperature. In order to specify test methods describing both (i) these in-service conditions of
flexible pavements and (ii) the underlying thermorheological behavior of asphalt, the four tests characterized by different thermal and mechanical loading are required:

1. The Tensile-Stress-Restrained-Specimen Test (TSRST) is used to simulate the inservice conditions of asphalt by restraining the deformation, while the temperature is
reduced by a pre-specified cooling rate;

2. The Uniaxial-Tensile-Strength Test (UTST) provides insight into the material resistance (tensile strength) at selected temperatures;

3. The Thermal-Shrinkage Test (TST) is used to specify the loading during cooling by determining the thermal shrinkage coefficient as a function of temperature; and,
finally,

4. Creep/Relaxation Tests (CTs/RTs) for identification of the viscoelastic behavior of asphalt at different temperatures.

In fact, the combination of all four tests is required to fully characterize the low-temperaturebehavior of asphalt when subjected to thermal and mechanical (tensile) loading. Based on the
obtained experimental results, key material parameters for ranking asphalts with regard to their low-temperature performance are critically reviewed. Moreover, the different test results
provide important insight for the development of material models for analysis-based prediction tools and enable the formulation of optimization parameters of low temperature
characteristics for mix design.

Evaluation of Simulated Load Techniques for Determining the Internal Angle of Gyration for the Superpave Gyratory Compactor

2019-08-03T09:29:12+00:00

Recently concerns have arisen regarding the inability of different Superpave gyratory compactors (SGC) to produce hot-mix asphalt (HMA) specimens with similar density. One proposed solution led to the development of the Dynamic Angle Validation (DAV) kit which measures the angle of gyration internally to the mold. DAV requires the use of HMA for the angle determination; logistical concerns and other issues led to the introduction of devices to mechanically simulate the load placed on the SGC by the mix being compacted. Two such devices – the Rapid Angle Measurement (RAM), which uses invelop load simulation (ILS) technology, and the Hot-Mix Simulator (HMS) – are described. Both simulation systems appear sound and applicable. Outstanding issues include SGC frame stiffness, the use of “cold” versus “hot” molds, comparisons of measurement systems, and the precision of internal angle measurements. Frame stiffness effects may require SGC calibration specifications to specify or reference the applied loading used. Internal angle measurements using simulated loading may be made with SGC molds at room temperature. The two proposed simulated loading methods may not yield the same value for internal angle on all SGC models. A definitive relationship between HMA stiffness and applied load to the SGC must be established to enable comparisons between internal angle measurements taken using hot-mix asphalt and taken using simulated loading.

Norwegian experiences and conclusions regarding Gyratory Compactors

2019-08-03T09:29:12+00:00

The Norwegian research project PROKAS was conducted in 19982004. One of the goals of the project has been to evaluate the suitability of the gyratory compactor for mix design of asphalt in stead of using the Marshall method. Another goal has been to establish a method for using the gyratory compactor for preparing specimens for further testing. The results are showing a variation between different gyratory compactors for the
same asphalt mixture that is not satisfactory regarding the compaction curves. Although the gyratory angle is set according to the description from the manufacturer, there is a significant deviation of internal angles in the mould during compaction between different compactors (and also between the top and bottom plate in the same compactor). There are also results indicating that the compaction curves are very sensitive to small changes in the gradation curve of the stone material. By testing different mix compositions of the same asphalt
mixtures that have performed well under traffic, recommendations have been made regarding how the compaction curves for an asphalt mixture should look like to perform well in the field. The Finnish compactors (ICT) used in Norway have the ability to measure the shear force applied to the specimen during compaction. The equipment used for measuring the internal angle have proven to be useful also for adjusting the levels of shear curves from different Gyratory compactors for comparing purposes. Based on an investigation for voids
distribution in the different parts of the specimens a method for preparing specimens for further testing has been chosen. This has been done despite of the fact that tests on specimen taken from the road show different levels of results.

Superposition principle to determine properties of bituminous mixtures in the time –temperature domain

2019-08-03T09:29:12+00:00

In this paper, it will be shown that several properties of asphaltic mixes fall within the domain of applicability of the time-temperature superposition principle. The exchangeability of not only the frequency and temperature (as often reported), but also loading speed and strain rate and temperature, allows application of a unique temperature susceptibility function for any asphaltic mix. This function is applicable, for elastic properties of asphaltic mixes e.g. flexural mix stiffness, as well as for inelastic properties e.g. compressive and tensile strength. An apparent advantage of this approach is the considerable reduction in testing programs.

Functional testing of asphalt mixes on field samples

2019-08-03T09:29:12+00:00

The Norwegian research project PROKAS was conducted in 1998 – 2004. One objective was to develop performance-based specifications for Norwegian asphalt mixtures. As part of this project a number of samples were taken from different asphalt pavements in Norway. Material properties as stiffness and deformation resistance were examined using the indirect tensile modulus test and the indentation repeated load axial test. The tests were carried out on the Nottingham Asphalt Tester (NAT).
Results show that NAT seems to give reasonable E-modulus ranking of asphalt mixes, while there are great variations in the results from the deformation tests. Questions are raised if the used procedure for measuring deformation properties has to be adjusted/improved, or if another method can be more suitable.
These investigations have given useful experience regarding the material properties of different asphalt mixes in Norway. However, further laboratory testing on field samples has to be conducted before specifications are established.

Evaluation of the stiffness modulus of bituminous mixtures using laboratory tests (NAT) validate by field back-analysis

2019-08-03T09:29:12+00:00

This paper concerns the evaluation of the stiffness modulus of bituminous mixtures by using the Nottingham Asphalt Tester (NAT). On the basis of indirect tensile laboratory test results, a practical model for stiffness modulus prediction in pavement bearing capacity analysis was established and calibrated for some typical bituminous mixtures used in Portuguese asphalt pavements. Validation of this model was based on two experimental fullscale pavements instrumented du ring construction. To study the bearing capacity of the
pavement structure, wheel load tests were carried out with simultaneous instruments measurements. Experimental pavements response modelling during load tests was performed using the finite elements method. The reasonably agreements between the calculated and measured strains indicate that the stiffness modulus prediction method is greatly reliable for the bituminous mixtures tested and could be very useful for further bearing capacity design of asphalt pavements.

Simplified Testing Method for Evaluation of Asphalt Mixtures for their Susceptibility to Permanent Deformation

2019-08-03T09:29:12+00:00

The accumulation of permanent deformation in the asphalt surfacing layer is considered to be the major cause of rutting in flexible pavements. Thus testing and methods of evaluation of mixtures for their susceptibility to permanent deformation have become important issues. This article reports further development of a mixture evaluation procedure previously suggested by the authors. The study considered the use of a simplified testing method, in which a slightly modified NAT (Nottingham Asphalt Tester) is used to measure axial and radial strains resulting from loading of cylindrical asphalt specimens. Two types of mixtures, Ab 16 (asphalt concrete) and Ska 16 (stone mastic asphalt) are considered in the study. Tests were conducted on specimens produced in the laboratory using both the repeated load triaxial test and Nottingham Asphalt Tester. The results of the tests were used to rank the two mixtures in terms of their resistance to permanent deformation. The two mixtures were also laid as a surfacing layer on a main road in southern Norway and rutting measurements were conducted in the field. Although the major part of the rutting is believed to come from studded tire wear, the relative performance of the two mixtures in terms of total rutting agrees with the ranking provided by the tests and the suggested evaluation procedure.

Prediction of Low Temperature Crack Spacing in Asphalt Pavements

2019-08-03T09:29:12+00:00

The recently released AASHTO Design Guide incorporates a number of models that address the different distresses that occur in asphalt pavements. The model used for low temperature cracking (called the Thermal Cracking or TC model) is based on a modified Paris law approach that is more appropriate for thermal fatigue type of cracking. Based on an empirical statistical analysis the model uses the crack propagation evolution to predict the number of cracks and the crack spacing that can develop during the life of a given pavement. A simple model was recently developed at the University of Minnesota based on the asphalt mixture tensile strength and the balance between the temperature shrinkage and the friction at the interface between the asphalt layer and the aggregate base. The model requires both asphalt mixture properties and aggregate properties and, similar to the TC model, predicts the crack spacing for a given pavement configuration. Unlike the TC model, it does not consider any crack evolution and cracks form instantaneously when the thermal stress in the asphalt layer exceeds the asphalt mixture strength. In this paper the two models are tested against field data from Mn/ROAD cells for which crack spacing information was available and recommendations for an improved crack spacing prediction model are made.

Some Insight into the Mixture Design of Large-Stone Asphalt Mixture for Airport Pavement

2019-08-03T09:29:12+00:00

In Japan recently large-stone asphalt mixtures have been introduced into the airport asphalt pavement to reinforce the pavement structure. So far they have been used as the base layer and/or the subbase layer materials. To reduce the rutting damages further and to prevent stripping between layers, it is expected to use the large-stone asphalt mixtures as the surface-base layer material. However, the raveling and cracking durability have not been thoroughly clarified. Therefore in the study a series of laboratory tests were conducted on the large stone asphalt mixture to evaluate the raveling and cracking characteristics in detail. For example, raveling tests were conducted to measure the groove deformation. Atmospheric exposure tests were performed to evaluate the asphalt deterioration characteristic. Same tests were also carried out on the conventional type asphalt mixture. Based on the test results, this paper focuses the effects of air void ratio in the large asphalt mixture on the bending strength-deformation, the raveling characteristics and the asphalt deterioration. It is found that there are suitable ranges of air void ratio to match the bending and raveling resistance to those of the conventional type asphalt mixture. Then the paper also suggests the appropriate air void ratio in the large-stone asphalt mixture for the surface-base layer.

Water susceptibility of asphalt mixtures: Testing the effect of adhesion agents on different binder/aggregate mixtures

2019-08-03T09:29:12+00:00

One of the objectives of the Norwegian PROKAS project 1998-2004 was better durability of asphalt pavements. In a laboratory study of water susceptibility of asphalt mixtures, tests were conducted on asphalt mixtures containing three common aggregates and bitumen 160/220. The aim of the study was to: a) compare three different test methods b) study the effects of different additives (liquid amine, hydrated lime, limestone and
combinations of these). The test methods were:

1) The “Cantabro test” after water conditioning of the asphalt specimen as described in prEN 12697-12.
2) “The Rolling bottle test” on the aggregate fraction 5.6/8.0 mm.
3) The Swedish "Shaking abrasion test", a modified version of the prEN 12274-7.

Hot mixed asphalt specimens with maximum aggregate size 2 mm were tested after water conditioning. The three test methods showed reasonably good agreement on the tested materials, even though they may be considered as complementary methods. The tests results showed that the use of adhesion agent should be recommended for certain aggregate/bitumen mixtures. For one of the binder/aggregate combinations none of the used adhesion agents were effective. All of the three test methods are recommended for durability testing for production control and for research and development.

Viability of using a bituminous sub-ballast layer on high-speed ballasted tracks

2019-08-03T09:29:12+00:00

The design of higher quality infrastructures reducing its life cycle costs is a major priority to increase the profitability of high-speed railway lines. The experience gained so far has evidenced the influence of track configuration on its maintenance costs. Recent railway research has shown that to fulfil a reduction of those costs one should act optimizing both the resiliency of the fastening system and the subgrade-sub-ballast system. With reference to this last aspect, the aim of this paper is to expose the first results obtained on a research project carried out by the authors concerning the viability of using a bituminous mix sub-ballast layer on the new Spanish high-speed lines. The interest of this solution to increase long-term performance of the track is discussed based on the available experience. Furthermore, the results of a parametric study evidences in what terms this solution can be technically feasible to reduce maintenance costs and increase service life of ballasted highspeed tracks.

A Railway Track Deflection Model Based on Nonlinear Discrete Support

2019-08-03T09:29:13+00:00

A nonlinear deflection model for railway tracks is developed for static or semistatic loads. The model is motivated by the fact that the load-deflection curve for a railway track is often, if not always, nonlinear with a hardening response. Hence a Winkler foundation is not appropriate as this represents a linear model - the beam on elastic foundation model. Euler-Bernoulli beam elements are used to model the rails, and the sleeper support is modelled by discrete nonlinear springs. The spring response is modelled by a simple power function with two parameters, thus providing a nonlinear behaviour. The analysis is based on measuring the rail deflection for two different load levels. A back-analysis using the nonlinear load-deflection relationship measurements is then carried out, which will give the numerical values of the two parameters in the nonlinear spring model. The rail deflection, rail bending moment and the rail seat loads can now be calculated. Assuming a hardening behaviour, the new model predicts a somewhat more extended deflection basin as compared with the beam on elastic foundation model with the same max imum deflection. Also, the maximum rail bending moment is somewhat smaller, while the maximum rail seat load attains a somewhat larger value. Thus, the new model can be said to give a stiff track response near the load application point and a softer response farther away from the load as compared with the beam on elastic foundation model.

Dynamic Loads Caused By Freight Trains With Wheelset Loads of 250 kN

2019-08-03T09:29:13+00:00

Increasing wheelset loads of freight trains to 250 kN leads to the question of whether the additional dynamic loads on the track are permissible. Moreover, the operating company (DB, German Railways) was interested in any differences of dynamic load caused by 2 axle and 3 axle bogies with their respective maximum axle loads. Dynamic loads on tracks consist of a low-frequency part caused by train geometry and train velocity, and a highfrequency part due to additional stochastic loads caused by irregularities of wheels, rails, etc. We performed seismic measurements during the passage of ore trains at track sections in Northern Germany where wagons with two and three axles per bogie were in use. Additionally, parameter studies with a Winkler beam model allowed comparison of the low-frequency behaviour of both types of wagon regarding particle velocity and displacement. The measurements are used to estimate the stochastic loads after filtering. The total load on track and subsoil caused by wagons with 6 axles and wheelset loads of 250 kN is compared with wagons with 4 axles and wheelset loads of 225 kN travelling at the same train speed.

Potential Remediation of Rail Track Foundations in Poorly Drained Clay Sites with Native Vegetation.

2019-08-03T09:29:13+00:00

One of the major issues concerning rail infrastructure owners is substructure maintenance. Inadequate intervention can lead to poor track geometry. The problem is compounded by the presence of expansive clays in the formation layer and is often exacerbated when poor drainage softens these clays, leading to progressive shear failures. In some cases full track reconstruction is necessary, which is extremely costly. Rail maintenance engineers observed better formation stability on these same clays where stands of trees had been established adjacent to the rail track. Subsequent investigation showed improved engineering subgrade properties in most cases due to relative soil desiccation. Accordingly, Australian Rail Track Corporation (ARTC) have planted several sites on its network with native vegetation.

Theoretical versus Measured Flexible Pavement Responses Under Dynamic Loading

2019-08-03T09:29:13+00:00

As mechanistic-empirical design of pavement structures advances toward full implementation, there is a need to evaluate the accuracy of theoretical load response models and backcalculation procedures employed in the design and analysis processes. To that end, a full-scale pavement structural study is underway at the National Center for Asphalt Technology (NCAT) Test Track to investigate the accuracy of the applicable models. Falling weight deflectometer (FWD) testing was conducted on eight different cross sections at the facility. The sections represented different pavement thicknesses, and use of modified and unmodified asphalt binders. FWD loads were dropped directly on top of and in close proximity to strain gauges and pressure cells embedded at different depths within the sections. This enabled the measurement of both surface deflections and in situ pavement responses under FWD loading. The surface deflections were used to backcalculate elastic layer properties within each test section. The properties were then used in forward calculation to compute stresses and strains at locations coinciding with embedded instrumentation. Direct comparisons were made between predicted pavement responses and measured responses to evaluate the effectiveness of both the backcalculation and forward calculation models. Better agreement was observed in the horizontal strain responses of the asphalt layer when compared to vertical pressures measured in the base and subgrade layers, respectively. However, it was generally found that layered elastic back- and forwardcalculation was sufficiently accurate for the conditions at the NCAT Test Track and also served to validate the sensor installation procedures.

3-Dimensional Finite Element Analysis of Cracking

2019-08-03T09:29:13+00:00

Pavement structural analysis aims at computing the pavement response under traffic and environmental loading. Excessive stresses induced by these two loading parameters lead to various types of distresses. One of the mos t important distresses is cracking. This paper focuses on traffic load induced cracking that either initiates at the bottom of bituminous pavement layers propagating upwards (bottom-up) or starts at the surface growing downwards (top-down). There is a need to investigate these types of cracking by establishing analytical models capable of simulating failure mechanisms, with the view to acquire a better understanding of the pavement behaviour so that the selection and design of maintenance treatments may be optimised. To this end, this paper presents three-dimensional models that were used for a detailed behavioural modelling of a pavement and for analysing both the distribution of stresses at the vicinity of single cracks and their effect on the overall pavement strength. The models were developed using LUSAS©, a general-purpose finite element computer program, and calibrated using Falling Weight Deflectometer (FWD) field data. A good convergence was achieved between the FWD measured deflections and those calculated by the models. Further analyses showed that the presence of cracking does not affect significantly the computed deflections but primarily the stress regime within the bituminous layer. In addition, the analyses demonstrated that top -down cracking may have a significant effect on the distribution of stresses within the bituminous layers. It should therefore be analysed as a structural defect, like bottom-up cracking.

3D Finite Element analysis of accelerated pavement test results from New Zealand’s CAPTIF Facility

2019-08-03T09:29:13+00:00

A nonlinear elastic model for unbound granular materials that was developed from the results of multi-stage Repeated Load Triaxial (RLT) Tests is described in this paper. The model was implemented in the 3-D FE-program FALTFEM. To check the validity of the model, comparisons were made with the results from accelerated pavement tests at Transit New Zealand’s CAPTIF Facility. The stresses and elastic strains within the test pavement at different depths were measured. A comparison was carried out to assess the accuracy of the elastic model by comparing the results of calculated elastic responses from the model using the nonlinear elastic DRESDEN Model and elastic solutions against the measured values. In addition an empirical approach was formulated and calibrated to determine basecourse plastic strain rate using data from RLT and CAPTIF tests of two different materials. From results of laboratory tests a good correlation
was found to exist between the elastic strain rate and the plastic strain rate as long as the shear stresses within the basecourse material are sufficiently small. However, by comparing the elastic/plastic relationship from RLT tests and the elastic/plastic relationship from CAPTIF tests differences could be observed. Shift factors were determined for the materials investigated, to predict the plastic strain rate in the field from RLT test results.

How may the variation of traffic loading effect measured asphalt strains and calculated pavement service life?

2019-08-03T09:29:13+00:00

Service life testing of asphalt specimen in laboratory frequently uses a highly specified and constant load. Real roads experience a considerable distribution of both placement and size of load which leads to a variety of material responses. Fatigue criteria derived from lab tests often need a large shift factor in order to match the experience on real roads. Data from an instrumented test site in southern Sweden (E4, Eket) has been used for analysis of how the variation in load placement, load size and response direction may contribute to the shift factor. The variation in measured strains at the bottom of the AC-layer has been compared with the Swedish design code ATB Road and has been used as input to the asphalt strain criterion in this code. The results are discussed with use of other contributions to the shift factor such as healing.

Investigation of Classification Parameters and Assumptions for Rigid and Flexible Airfield Pavements

2019-08-03T09:29:13+00:00

Classification of airfield pavement bearing capacity has always been one of the most important tasks for their management and therefore it is important to have a suitable classification and reporting system, which will internationally facilitate the management of airport pavements. Currently the method used for this purpose is the Aircraft Classification Number – Pavement Classification Number (ACN – PCN) of the International Civil Aviation Organization (ICAO) however, practice has shown that there are several difficulties and drawbacks, which encumber the implementation of the method. Theoretical investigations on the method assumptions and background, as well as analyses of field applications have revealed several findings regarding the accuracy and reliability of the reporting system. Related analyses based on data from Greek and international airfield pavement structures have shown that in practice the ACN-PCN system for rigid pavements is less sensitive to background parameters and assumptions, easier to apply and probably more accurate compared to flexible pavements. In addition, critical details which should be considered in order to optimize the accuracy and reliability of the ACN in practice are presented and discussed.

Calculation and Forecast of Settlement of widened embankment

2019-08-03T09:29:13+00:00

The 2-D FEM has been employed to analyze the settlement of widened embankment and the interactional behavior of new and old embankments. In the calculation the elastic-plastic constitutive model (Drucker-Prager model) and constitutive model of interface with no thickness have been applied to consider the plasticity of soils and the nonlinear behavior of Interface element. This text gives the result of settlement according to the modeling method. The comparison between the predicted and measured values proves that the constitution and the models are reliable.

A STUDY ON THE EFFECT OF FAILURE PROBABILITY OF DESIGN FATIGUE CURVE ON THE RELIABILITY OF CONCRETE PAVEMENT

2019-08-03T09:29:13+00:00

The design fatigue curve for concrete pavement must be considered the probability of failure because the fatigue lives of concrete show a large scatter, and the probability of design fatigue curve has a great influence on the reliability of concrete pavement. But the relationship between the failure probability of design fatigue curve and the reliability of concrete pavement was not cleared therefore there were no realistic guide for the choice of the failure probability of design fatigue curve. In this paper, this relationship was studied by the result of performance survey about the concrete pavement under service period of 25 years.
According to the survey result, the rate of cracked slabs of this concrete pavement was about 30%. On the other hand, the calculation result of fatigue damage of this concrete pavement using the failure probability of 30% fatigue curve was 1.0 for the calculation period of 20 years. This means that this concrete pavement cause the fatigue crack after 20 years service. Consequently, it is appeared that the reliability of concrete pavement can predict by the failure probability of design fatigue curve.
And more, from the flexural fatigue test results of specimens obtained from the survey area, the validity of the Miner's rule for cumulative fatigue damage of concrete was verified.

Analytical Study on Evaluation of Subgrade Modulus Using Portable FWD

2019-08-03T09:29:13+00:00

In a portable FWD test, the variations on the loading time and its integration influences the estimated elastic modulus and K-value of subgrade even if the peak load is the same. The aforementioned could not be found from the impact numerical FEM analysis of elastic model for the portable FWD. In this research, analytical study has been carried out to investigate the influence of various parameters, such as the mass and the drop height of the
falling weight, on the loading time and its integration from the numerical analysis of viscoelastic model.

Long-term Evenness of Pavements with Respect to Soil Deformations

2019-08-03T09:29:14+00:00

Today’s requirements of comfortable and fast travelling continue to increase. Thus it is necessary to secure a long-term evenness of the pavement. The evenness is depending on the homogeneity of the subsoil. Measurements indicate that the spatial variation of soil stiffness and pavement unevenness have the same statistical characteristics. It can be posted that the evenness of the pavement is a function of the spatial variation of soil stiffness, number of vehicle passes and dynamic loads. The dynamic loads depend on the dynamic characteristic of the vehicles, their velocity and the evenness of the pavement. A simple numerical model is outlined to demonstrate this mechanism of developing unevenness with number of vehicle passes. This gives a chance to establish necessary requirements for the tolerable spatial variation of soil stiffness with respect to the raising requirements of driving comfort.

Probabilistic Forecasting Model of Pavement Performance Based on BP Neural Network

2019-08-03T09:29:14+00:00

Applying BP(Back Propagation) neural network to the forecasting of pavement performance promotes the idea that neural network can be combined with Markov random process, trains neural network with fix structure by making use of time series of performance state of pavement and thus establishes the neural network probabilistic forecasting model of pavement performance.

The PERS System for Modelling Pavements Performance Based on Incremental-Recursive Techniques

2019-08-03T09:29:14+00:00

PERS is a software package developed by Dynatest for lifetime pavement analysis and pavement managment. The concept is to use incremental-recursive models to predict the future damage to the pavement, from present pavement condition and the effects caused by traffic laoding and climate. When the pavement condition hav sbeen evaluated during field testing in terms of elastic moduli, roughness, rutting etc, PERS calculates the future performance, in yearly or seasonal time increments, using user-defined damage models. Based on the traffic loads and strcutural information the stress/strain levels are calculated for each layer, and the damage to all condition parameters for the sweson is derived for mthe modles. The resulting pavement condition is the n used, recursively, as input for the next time increment. By comparative graphics or perdicted performance and historical condition data from field testing, it is possible to evaluate and calibrate the models to fit the measured paerformance of the pavement. Simulation of rehvailitation activities cand be performed, by applying a rehabilitation alternative in any year of the analysis period. Many effects can be studied graphically, like all relevant costs to hte agency and the users. Cost models can be user-defined. Further it is possible to let PERS calculate rehabilitation plans for the section. using a database of rehabilitation alternatives . and predfined critical limits for the condition data. Lastly it is possibe to use all sectional rehabilitation plans in a budget based optimization, to find the overall most cost-effective solution for a road network.

Semi-rigid Asphalt Pavement's Premature Failures on Chinese Motorway Network

2019-08-03T09:29:14+00:00

Over the past 20 years more than 30,000 km motorways have been built in China. On the motorway network, semi-rigid asphalt pavement is widely used, which is composed of 15cm or so asphalt concrete layer and cement or lime-flyash bounded aggregate base layer. It has been observed that many premature failures occur 2-3 years after the motorways' open to traffic. Moreover, most of the motorway asphalt pavements' actual service life is about 7-8 years, comparing with their design life of 15 years. In the paper, asphalt pavement design method of China is given first. Then, the premature failure types as rutting and transversal cracking are presented. The impact of these failures on the pavement is discussed as well. It reveals that currently prevailing semi-rigid asphalt pavement technique in China need to be further improved.

Predicting the Resilient Modulus of Unbound Granular Materials by Neural Networks

2019-08-03T09:29:14+00:00

The process of pavement design requires the provision of material properties. For mechanistic–empirical design methods, the resilient modulus represents the most suitable alternative for describing the behavior of aggregate materials commonly used in sub-base and base layers. However, the adoption of the resilient modulus has been slow due to the complicated nature of the laboratory test used to obtain the parameter and its cost. Attempts to correlate the resilient modulus to the widely used California Bearing Ratio and other empirical parameters in the past fall short of providing reasonably accurate estimates of the parameter. With the renewed interest in using the resilient modulus as advocated by the AASHTO 2002 Guide, a quick and inexpensive solution to provide accurate estimates of this parameter is needed. This paper presents the artificial neural network (ANN) technique as a promising method that can help designers have a good first-step estimation of the resilient modulus based on data accumulated over the years. The study h ighlights the use of ANN technique, which utilizes simple parameters as input to predict the resilient modulus of unbound granular materials. Results of ANN simulations confirm the potential of the technique to predict the resilient modulus of compacted samples tested at various compaction densities, state of stress and moisture contents. Such a tool represents an attractive alternative to laboratory testing for small jurisdictions with limited budget and personnel.

Road Map to Develop Methodologies for Determining Remaining Pavement Service Life

2019-08-03T09:29:14+00:00

Pavements are a vital component of the transportation system and represent a substantial investment. Pavement condition is an important indicator of overall highway system performance. The monitoring and evaluation of pavement condition is an essential part of pavement management. Ideally, determining the remaining pavement service life would assist in making decisions about preventive maintenance, preservation, rehabilitation, or reconstruction. There are several approaches being researched and developed to acquire and
to analyze data on pavement condition. This paper will discuss a strategic road map to develop methodologies for determining remaining service life of pavements. The paper will present the current state-of-the-practice in the U.S. as well as opportunities for developing other analytical procedures.

Prediction of Deformation Behaviors on Stress-Dependent Unbound Pavement Foundations

2019-08-03T09:29:14+00:00

There are several major practical consequences of the stress-dependent and deformational properties of unbound pavement foundations. Among those are the modulus and Poisson’s ratio’s that may change, the compressive stresses that are generated in such materials under load, the stiffening and strengthening effect of repeated loading to progressively increase the unbound pavement materials resistance to permanent deformation. The predictions of deformation on stress-dependent unbound pavement foundations are presented in this paper by finite element analyses and a combination of field observations of accelerated loading tests results.

Rehabilitation by cracking and seating of concrete pavement optimized by FWD analysis

2019-08-03T09:29:14+00:00

One of the main roads to the town of Copenhagen was constructed in 1942 during the Second World War as a 4 lane concrete pavement. The slabs are constructed directly on the clay subgrade using a 50 mm slag material levelling layer. The pavement has, despite of a traffic load of about 150,000 10t ESAL per direction per year, functioned until today, but over the last 10 years in a very poor condition. The preliminary investigations revealed that several of the concrete slab corners were badly supported, that the soil below the concrete had surface E moduli of down to 35 MPa, while the clay material had CBR values of down to 19 %. A preliminary design with estimated E values of 6,000 MPa for the cracked and seated concrete layer resulted in a designed asphalt overlay with a thickness of 170 mm for 6.0 mill. 10t ESAL equivalent to a design period of approx. 40 years. In the Spring of 1999 a small test section was selected. The concrete pavement was cracked and seated
and FWD measurements were carried out. The measurements resulted in design E values of the cracked
and seated concrete slabs of 1,600 MPa. The redesign resulted in an asphalt overlay thickness of 200
mm for 4.8 mill. 10t ESAL equivalent to a design period of approx. 32 years. After construction of the asphalt layer, the FWD measurements on the asphalt surface revealed that the E values of the cracked and seated concrete layer had changed to 7,000 MPa over the cracks. These results were later confirmed partly by measurements carried out one year later during the second half of the rehabilitation of the old concrete pavement, partly by measurements carried out two years after the construction.

Performance-based design method for railway asphalt concretereinforced roadbed

2019-08-03T09:29:14+00:00

The asphalt roadbed (asphalt concrete-reinforced roadbed) is widely used for ballasted tracks in Japan, primarily to firmly support ballasted tracks and to reduce track irregularities. The current design standard of asphalt roadbeds in Japan does not take into account the effects of the number of train passing. To alleviate this drawback, it was necessary to develop a more rational performance-based design method that can reduce the total life cycle cost. It is considered that the new performance-based design of railway asphalt roadbeds should be based on fatigue criteria for asphalt concrete. In the design of pavement for highways, the fatigue criteria of asphalt concrete are specified in terms of maximum resilient tensile strains that are evaluated by multi-layer elastic analysis. However, it is not known whether the same methodology can be applied to railway roadbeds, which are subjected to much more complicated load conditions due to complicated track structures, composed of rails, sleepers and ballast. In this study, a series of scale model tests were performed to validate the three-dimensional elastic FEM analysis to evaluate resilient strains in the asphalt concrete layer in railway roadbed. On the ground of that, appropriate analysis procedure to obtain the asphalt concrete strain was proposed in present study. Thereafter, the service life of asphalt roadbed was obtained by new design method. It was confirmed that the current asphalt roadbed has a service life of 50 years in general high speed line in Japan.

Revision of the French reference document of frost design method for High Speed Railway Lines.

2019-08-03T09:29:14+00:00

The revision of the project of typical railway structure s catalog has lead Société Nationale des Chemins de Fer français (SNCF) to consider a modernization of its “frost design method”. In particular, high speed railways required very severe levelling margins. Very high speeds need perfect evenness to prevent any defect of lengthwise level, which would generate unballasting risk and vertical movement injurious for the lifetime of structures. A collaboration has been engaged with the Laboratoire Régional des Ponts et Chaussées (LRPC) de Nancy. The aim was to build a new technical SNCF reference document using the design pavement method developed by the network of Laboratoires des Ponts et Chaussées. during the past three decades. This approach is based on thermal modelling of structures and winter characterization through the freezing index concept.
The process followed for the realization of this document consisted in reproducing the scheme employed for the road frost design method, adjusting it to the railway problematic. Indeed, besides use’ specifities, rain penetrates railway structures. Energy exchanges are enhanced with atmosphere, the water continuously modifying physical properties of railway components. Moreover, use of atypical materials for roads builders, such as ballast, obliged additional laboratory tests in order to know their physical properties and thermal behavior.

Ballastless Tracks on Asphalt Pavements

2019-08-03T09:29:14+00:00

During the last three decades different types of ballastless tracks have been developed, tested and built in high speed lines of the German DB-AG.:
- single rail supports directly fixed on a pavement (CRCP only).
- prefabricated, prestressed slabs or frames connected to a treated base
- sleeper panels rested on a pavement (AC or CRCP) or connected in a monolithic way (CRCP only)

The axle loads of railway vehicles are much higher compared to heavy trucks. But due to the good load distribution reached by rail and resilient rail supports and due to a sufficient contact
area between sleeper and treated base the contact pressure on pavement surface can be decreased. Therefore asphalt pavements offered suitable solutions for ballastless track
developments. The concrete sleeper panel must be fixed by suitable components to the asphalt pavement to handle the horizontal forces caused by traffic and by temperature changes. The weight of sleepers should be considered in respect of rail uplift forces. In addition to the bearing capacity for asphalt pavements the occurrence of deformations caused by the time and temperature dependent visco-elastic behaviour of asphalt must be taken into consideration. Due to the accuracy of the vertical track-alignment according to the design speed up to 300 km/h and more and due to the sufficient surface drainage the deformations must be limited, but enable better adaptation at the interface between sleeper and pavement. Experiences born at test sections and revenue lines are given.

Mitigation of ground borne noise in rock railway tunnelsPart I: Track design and simulation

2019-08-03T09:29:14+00:00

Railway trafc in shallow depth rock tunnels can give unacceptable levels of ground borne noise in buildings above the tunnel. For such a tunnel under construction in Norway a project involving full scale testing was commissioned by the Norwegian Rail Administration (JBV), with the aim of designing the most cost effective track that satised the prescribed residential sound levels. Evaluation of various track designs was based upon the results of a numerical model of the wagon-track-tunnel system. This model and the corresponding input parameters are the focus of this rst part of a two part paper; the second part concentrates on the full scale tests. The numerical model presented herein is a one dimensional model of the suspended railcar, rail, sleeper, railway substructure (ballast, ballast mats and backll) and tunnel oor. The model comprises mechanical mass-spring-damper elements and geolayer elements embodied by the one dimensional wave equation. Verication against results from other contributors is presented, and the model is shown to give high quality results with a modicum of computation. The properties of the constituent track materials are also discussed in this paper, with particular attention paid to the in-situ stress conditions.

Mitigation of ground borne noise in rock railway tunnels - Part II: Full scale tests

2019-08-03T09:29:15+00:00

Railway trafc in shallow depth rock tunnels can give unacceptable levels of ground borne noise in buildings above the tunnel. For such a tunnel under construction in Norway
a project was commissioned by the Norwegian Rail Administration (JBV) to design the most cost effective track that satised the prescribed residential sound levels. A component of
this project was a series of full scale tests. This, the second part of a two part paper, discusses these full scale tests and compares the measured results against those predicted by the simulation work of the rst part of the paper. For each of the seven track substructures tested the acceleration of the rail, sleeper, tunnel oor and tunnel wall were recorded, in addition to the acceleration at various depths throughout the track substructure. Vibration and sound were also measured in the houses above the tunnel. The input to the entire system was via a fully laden freight wagon which had a dynamic excitation force applied to one axle. This force was excited by a hydraulic actuator which, operating under force control, delivered excitation in sweeps of one-third octave bands that covered the relevant frequency range. This paper presents the testing program and corresponding results, and compares these results with the predictions of the companion paper.

Pavement Strengthening and Rehabilitation in Norway - Assessing the needs

2019-08-03T09:29:15+00:00

The Norwegian Pavement and Materials Design Guidelines were revised in 2005. A new system for road strengthening and pavement rehabilitation, based on an evaluation of the surfacing service life, was then introduced. In this new system the strengthening need is based on the Surfacing Life Factor (SLF). The SLF describes the relation between the functional (observed) surfacing service life and the expected surfacing
service life. Depending on this factor the need for strengthening is given:

SLF above 0,7 - the required strength improvement is considered to be taken care of by the ordinary resurfacings.
SLF 0.7 - 0.5 - the required strength improvement is expressed in term of structural number values and depends on the SLF and traffic volume.
SLF below 0.5 - indicates a pavement structure with serious deficiencies and a full investigation is required.
The change has been made possible by the introduction of the Norwegian pavement management system in 1990.

Parametric Sensitivity Analysis for the FAA’s Airport Pavement Thickness Design Software LEDFAA-1.3

2019-08-03T09:29:15+00:00

LEDFAA-1.3 is a computer program for airport pavement thickness design. It implements layered elastic theory based design procedures developed under the sponsorship of the Federal Aviation Administration (FAA) for new and overlay design of flexible and rigid pavements. The layered elastic procedures, as implemented in the program, are the FAA airport pavement thickness design standards referenced in Chapter 7 of Advisory Circular AC 150/5320-6D, change 3. The core of the program is Leaf, a layered elastic computational program implemented, in this case, as a Microsoft Windows™ ActiveX dynamic link library written in Visual Basic™ 6.0. Pavement thickness design needs many input parameters and different input parameters have different influences on the pavement life. Pavement life is insensitive to some parameters, a small change of the parameter has only limited effects on the pavement life; however, for other parameters, life is very sensitive to changes in their values; a small change will lead to significant change of the pavement life. Sensitivity analysis is a powerful tool to clarify, verify, quantitatively understand, and compare existing airport pavement design specifications. The results and findings of the study provide essential information in modifying and improving the existing specifications and developing new ones. Results from a parametric sensitivity analysis are presented in this paper. The findings are being used to modify and improve the existing FAA airport pavement thickness design models and in the development of the new FAA design models.

Austrian Design Standards for Block Pavements

2019-08-03T09:29:15+00:00

The Austrian specification for pavement design which was modified the last time in 1998 consists of a catalogue type of stand ardized structures for bituminous and concrete pavements. Recently, an extension of this guideline by new pavement types was completed, covering block pavements and small slabs of concrete as well as of natural stones. The paper gives an overview on the structure of the specification, the underlying analytical design calculations, and on the new pavement types and their limits of application. The new version of the guideline was published recently.

Design of flexible pavement layers

2019-08-03T09:29:15+00:00

Several research projects realised by the Chair of Pavement Engineering at the Dresden University of Technology aim at the development of an analytical design method to predict the stress and strain behaviour of a pavement or to calculate the remaining life cycle of the pavement structure. The developed dimensioning model is based on the fundamental idea of freely choosing any possible construction (flexible pavement). Furthermore, the dimensioning model aims at the optimisation of the pavement construction considering traffic loading and weather-induced factors. Using different materials, the particular thickness of each layer is optimised on the basis of failure hypotheses.

Estimation of the Sensitivity of Design Input Variables for the Mechanistic-Empirical Design Guide

2019-08-03T09:29:15+00:00

Many highway agencies use AASHTO methods for the design of pavement structures. Current AASHTO methods are based on empirical relationship s between traffic loading, materials, and pavement performance developed from the AASHO Road Test (1958-1961). The applicability of these methods to modern-day conditions has been questioned; in addition, the lack of realistic inputs regarding environmental and other factors in pavement design has caused concern. Research sponsored by th e National Cooperative Highway Research Program has resulted in the development o f a mechanistic-empirical design guide (M-E Design Guide) for pavement structural analysis. The new M-E Design Guide requires over 100 inputs to model traffic, environmental, materials, and pavement performance to provide estimates of pavement distress over the design life of the pavement. Many designers may lack specific knowledge of the data required. A study was performed to assess the relative sensitivity of the models used in the M-E Design Guide to inputs relating to construction materials in the analysis of flexible and rigid pavement structures. Inputs were evaluated by analyzing a standard pavement section and changing the value of each input individually, then assessing the change in predicted pavement distress (cracking, faulting, and roughness for rigid pavements; rutting, fatigue, and low-temperature cracking for flexible pavements). The evaluations may aid designers in focusing on those inputs having the most
effect on desired pavement performance.

Design of a specific bituminous surfacing for orthotropic steel bridge decks : application to the Millau Viaduct

2019-08-03T09:29:15+00:00

This paper presents a rational approach for the performance-based design of bituminous wearing surfacings on orthogonally anisotropic steel bridges. Basically, the behavior of bituminous surfacings on steel orthotropic decks, under heavy truck traffic and environmental conditions, is highly complex. Both the geometry of the structure and the very high flexibility of metallic plates make the deformations and stresses very severe in steel bridge surfacings. In particular, the repeated loading make the fatigue strength be an important parameter for the design of such bituminous wearing courses. In addition, these specific surfacings must also have durability over the expected temperature range: it must be
resistant to thermal cracking at low temperature and to rutting at high temperature. The technical studies led in parallel to the construction of the Millau Viaduct (France) –the tallest bridge in the world– have provided in particular the opportunity of new progress in the development of appropriate laboratory testing equipment and of original polymer-modified surfacing. Indeed, APPIA pulled the socks up and led a comprehensive research program including both a large laboratory testing campaign and a Finite Element analysis so as to develop a handy tool for design of plate surfacings. Eventually, as regards the realization of this one-off work, the bringing into play of considerable resources made APPIA succeed in delivering within the deadlines a surfacing of the highest standard for the Millau Viaduct.

A non-linear elastic material model and its application in pavement design

2019-08-03T09:29:15+00:00

A non-linear elastic material model with a stress level control defined by the Mohr-Coulomb yield criterion has been developed, implemented, and tested in practice. The model is developed for unbound granular base materials in conjunction with relevant test methods. In the design process the material model is used to predict pavement response and theoretically confirm a stabilized behavior in the base material during cyclic loading. Input parameters for the model are directly linked to practical field tests where design parameters can be validated in-situ during the construction of the pavement. Critical parameters are void ratio, isotropic mean stress, and matric suction. The in-situ mean stress is here the accumulated effect of both compaction induced residual stresses and the contribution due to matric suction. The in-situ mean isotropic stress is estimated indirectly from seismic measurements. The matric suction in the unbound granular material is measured with gypsum blocks. The practical usefulness of the proposed model is demonstrated with a case study where the pavement construction is economically optimized based on available materials. Results show that the model can accurately predict the non-linear pavement response based on the material properties measured during construction.

Design of Proof Rolling Regimes for Heavy Duty Aircraft Pavements

2019-08-03T09:29:15+00:00

Proof rolling of aircraft pavements is an Australian practice that is designed to reveal pavement layer deficiencies prior to the construction of the next pavement layer. There are a number of heavy pneumatic-tyred proof rollers available in Australia for this purpose. These rollers are predominantly owned by the Department of Defence and made available to airfield constructors, on a project-by-project basis. The selection of rollers and the design of proof rolling regimes should utilise the stress with depth calculation function of layered elastic design tools such as APSDS. Proof rolling regimes can be determined by comparison of aircraft and roller induced plots of the damage indicator with depth. The traditional use of Boussinesq’s equation for simple load stress with depth in a single elastic layer is also viable for many practical applications. Strain and deflection could also be used as the damage indicator but stress is the most effective as the pavement structure, subgrade strength and location of the damage indicator have little effect on the calculated stresses. A single layer representation of the pavement is also adequate. More specific cases, where the absolute values of the damage indicator are required or where non-typical pavements are to be designed, a customised pavement structure may be justifiable for the roller and aircraft induced stress calculations.

Selection of Input Parameters for Layered Elastic Design of Flexible Aircraft Pavements

2019-08-03T09:29:15+00:00

The Australian developed layered elastic tool for flexible aircraft pavement design, Aircraft Pavement Structural Design System (APSDS) is based on the road design program, CIRCLY. One of the advantages of APSDS (and some other layered elastic tools) over purely empirical design methods is that the designer can select and control all input parameters. The operation of this tool is relatively simple. However, unless appropriate input parameters are selected, gross errors can result. The required parameters include subgrade strength, standard deviation of aircraft wander, aircraft masses, tyre pressures and aircraft passes, as well as asphalt modulus and pavement composition. The selection of parameters, including their relative importance, is discussed and indicative values are provided for many input parameters.

Pavement Response due to Torsional Surface Loading

2019-08-03T09:29:15+00:00

When heavy vehicles such as truck and trailer make a sharp turn, it is known that torsional as well as vertical loads are exerted on the pavement surface. However, analytical solution of elastic multi-layered systems is not known. This paper presents the solution for multilayered elastic systems subjected to uniformly distributed torsional loading over a circular area. By combining this solution with the solutions of uniform vertical loading on the same circular area, one can estimate pavement response due to both types o f loadings.

Structural Design of Pavement for Cold Regions based on Life-Cycle Cost

2019-08-03T09:29:15+00:00

Asphalt pavements in Japan are commonly designed with a 10-year life, regardless of the importance and traffic volume of the route. Toward minimizing the life-cycle cost by extending the service life, the Hokkaido Regional Development Bureau recently revised structural design standards for asphalt pavement to extend the design life to 20 years in cold Hokkaido. The revision focused on low-temperature cracking, frost heaving, and phenomena of cold, snowy climates, as well as on the route's importance and traffic volume. Comparison was made between pavement with a 10-year design life and that with a 20-year design life. Analysis based on multi-layer elasticity theory estimated the number of years before fatigue fracture occurs. Performance curves were obtained by regression analysis of data on longitudinal and transverse profile of the road. Based on these, 50-year life-cycle costs were calculated for 10-year and 20-year design life pavements. A separate case study on national highways in Hokkaido confirmed that extending the design life from 10 years to 20 years could reduce the life-cycle cost more than 10 %.

Rehabilitation of Airport Pavements: The Experience of Linate Airport

2019-08-03T09:29:16+00:00

At Linate Airport (Milano – Italy) in August 2002 the rehabilitation of the runway pavements was carried out. The works concerned both the asphalt pavements of the runway and the concrete slabs of the 36R Threshold Area. For both the pavements the works were characterized by preliminary studies and experimental research (started in 2001), by a very severe control activity during the works, by many measures after the works to verify the results. Many constraints, especially the need to complete all the works in only 20 days of August, forced to study solutions (in some cases completely innovative such as the new wide slabs 10,0 x 15,00 m) which were able to optimize design and building. The present paper discusses the experience carried out and the results obtained, with the aim to allow other Airport Authorities and technicians to find solutions when facing with similar problems and needs.

The traffic load components in pavement analysis

2019-08-03T09:29:16+00:00

This paper aims to illustrate the influence of the load model (in particular the components of traffic load) in pavement analysis. Firstly, a state-of-art of the load models for pavement analysis is presented. The load components (contact stresses), their magnitude and the tire-pavement contact area are referred to. Secondly, one analyses the influence of the load
components for pavement analysis by modelling, with the Finite Element Method (FEM), three flexible pavement structures, referred in the Portuguese Pavement Catalogue (JAE,
1995) for the traffic class corresponding to 500-800 heavy vehicles a day. The selected pavement structures differ with regard to geometry and pavement materials. The three
structures are modelling, in 3D, with DIANA software adopting materials as linear elastic, with different load models. The main conclusion of this work is that the consideration of the
three components of load (with uniform distribution) may not substantially alter the numerical results obtained with the exclusive consideration of vertical component of the load.

Use of MnROAD to Support the Development and Further Refinement of the Current Mechanistic Design Guide

2019-08-03T09:29:16+00:00

This paper is a review the use of the Minnesota Road Research Project (MnROAD) to support both the adaptation and further refinement of the 2002 Mechanistic-Empirical Pavement Design Guide (ME-EPDG). It shows that the MnR OAD facility provided the developers of the M-EPDG very valuable and unique information that was valuable in during the development of the M-EPDG. It is now a valuable asset for pavement researchers to use to refine the M-EPDG for local calibration and validation efforts.

Light-weight aggregates as frost protection in roads

2019-08-03T09:29:16+00:00

Large deformations and reduced bearing capacity caused by frost heave and thawing every cause significant problems and result in major maintenance costs of the roads in the Nordic contries. Extruded polystyrene has been the most preferred material for frost protection for some years. However, light weight clay aggregate (LWA) has now become a regular material used for frost insulation in roads in Norway based on a rresearch project by SINTEF. To optimize the design, SINTEF has performed a number of numerical analyses and develop a design chart that gives the required layer thickness for frost insulation. The design chart in the lastest Norwegian guidlines for road construction, Handbook 018 Road Construction, is based on this design chart. The calculations showed that the frost protection layer using LWA should be 3-5 times thicker than a frost protection of extruded polystyrene (XPS).

The development of a new road design method in Sweden

2019-08-03T09:29:16+00:00

Since 1998, Sweden has been conducting a strategy for developing a new model for road design, including implementation of ethis model. Today a new model for calculation of stress and strain is ready. It can do calculations for asphalt pavement with viscous elasticity and unbound material with non-linear elasticity. In spring 2005, the model is to be supplemented by calculation modules for permanent deformations in bituminous bound layers and in unbound layers, based on the theories behind the new AASHTO “Design Guide”. Implementing this model has involved three years of continuous training of new road designers in Western Sweden, with participation of consultants and contractors. During the winter and spring of 2004/05 six different projects were chosen to demonstrate the new model. Road quality is to be improved by “active design” on site. Unbound material is to be tested by triaxial tests, and there are to be calculations of future permanent deformations. The results are to be used in deciding pavement thicknesses for different parts of the road. Road pavement optimizationroad in this way will save a lot of money. A better
design method and relating test methods should also make it possible to avoid most of the problems of early failure of roads.

Elastic Wave Measurement System Using FWD for Asphalt Pavement

2019-08-03T09:29:16+00:00

This paper describes stiffness estimation methods for the base layer of asphalt pavement using quasi-static back-calculation, dynamic back-calculation and transit elastic wave measurement system. These techniques are based on FWD devices: FWD (50kN load capacity), a portable type of FWD (15 kN load capacity) and a new type of portable of FWD (25 kN load capacity). The surface acceleration is measured by outer accelerometer of FWD devices. The system consists of a portable PC, a sampling AID card, an acceleration system, FWD or a portable FWD and MATLAB-based software. It revealed that the stiffness of base layer was less influenced by dynamic back-calculation or transit elastic wave measurement system. It was confirmed that the transit elastic wave measurement can be used to evaluate the stiffness characterizing the mechanical response of the pavement at each tested site.

Assessment of the Danish High Speed Deflectograph in France

2019-08-03T09:29:16+00:00

The High Speed Deflectograph (HSD), developed by the Danish Road Institute and Greenwood Engineering A/S, measures the speed of vertical deformation of the road surface under the action of a load by means of two laser sensors with Doppler effect. During autumn 2003, LCPC assessed this prototype in the north of France. To make the tests, three different routes (motorway, trunk road and secondary road) were selected. Each route comprised a 2 km test section on which the HSD carried out several runs. The FWD took measurements on the same sections. Measurements of the HSD comprise the slope of the tangent to the basin of deflection at the point of measurement of the Doppler sensor. This parameter relates to the bearing capacity of the roadway and is the object of the analysis, which comprises the calculation of the repeatability on measurements of the test sections and the comparison of the values of the HSD with those of the FWD. Comparisons with the Flash deflectograph were also made. The conclusions of the study underline that HSD measurements are repeatable and could detect clear differences in levels of deflection. Following this assessment, a new HSD prototype has been designed.

Measurement of Wheel Wander Under Live Traffic Conditions

2019-08-03T09:29:16+00:00

A critical parameter to measure for any type of pavement structural analysis is the precise location of the applied load. Under live traffic conditions the placement is random (termed wheel wander) and is important to characterize since it defines the transverse location and severity of pavement distress. As more test roads are built with embedded instrumentation to support the calibration and implementation of mechanistic-empirical (M-E) pavement design, the load placement relative to the instrumentation must be determined. Also, it is necessary to assess whether the wheel wander under test conditions is representative of open-access facilities. In this research, a lateral-position measurement system, comprised of independent axle sensing strips, was installed at the National Center for Asphalt Technology (NCAT) Test Track to measure wheel wander of the traffic. The Test Track is a 1.7 mile (2.7 kilometer) cooperative research test road trafficked by five tractor-trailers operated by ten drivers over two shifts per day. This paper details the lateral-position measurement system, the installation process, the calibration process and the algorithms to compute lateral offset. Data collected over two trucking shifts are presented, comprised of over 3,000 axle passes, and indicate a normal distribution of wheel wander at the Test Track having a standard deviation of 8.6 in. (21.8 cm), consistent with measurements made at openaccess facilities.

Measuring Pavement Deflection Variance at Highway Speeds

2019-08-03T09:29:16+00:00

A new method for testing pavement condition combines laser/inertial profilometry of unloaded pavement with vibration measurements in a full loaded heavy truck at highway speed. Three types of results are obtained. 1: Truck wheel, frame and cab vibration, as well as driver seat vibration to be compared with exposure guidelines in ISO 2631-1 and limits in directive 2002/44/EC. 2: Three-dimensional road surface geometry data for simulation of ride and calculation of roughness indices. 3: Locations of potential pavement "soft spots". The latter is possible since large pavement deflection variance under the heavy truck cause a quite different vehicle vibration pattern than the pattern excited from the measured unloaded road surface profile. A tentative accuracy experiment has been done at 4 sites. Recorded seat vibration levels were very high, thus exceeding the EU Action Value in all test runs. The soft spot indications show reasonable repeatability, as well as reproducibility between different driving speeds and between spring time and autumn. Trueness is the most
difficult accuracy feature to estimate, since no ideal reference method is at hand neither for variance of local deflection under truck wheel, nor for global deflection under the entire truck. By comparison with FWD, coring and ground penetrating radar results, trueness seems promising. During the tests, a virtual tyre footprint sensor was used for road profiling. Evaluation showed it to bring a large improvement to profiling accuracy. The new high speed measurement method brings excellent opportunities for further research on the entire chain pavement-truck-ride quality interaction.

Ground-Penetrating Radar Applications for the Assessment of Airfield Pavements

2019-08-03T09:29:16+00:00

Growing volumes of aircraft traffic and the introduction of heavier aircraft are significantly impacting airports around the world. Pavement management systems are being relied upon heavily to monitor pavement condition, forecast performance, and plan for timely maintenance activities. The most widely used tools for maintenance and rehabilitation management for airfield pavements have been the falling weight deflectometer and dynamic cone penetrometer. However, these commonly used tests do not provide adequate information with respect to the thicknesses of individual layers within a pavement system. The layer thicknesses must be known in order to backcalculate the structural capacity using nondestructive test results. Supplementing these commonly used test procedures with core samples is disruptive, costly, and time consuming. Rapid, nondestructive techniques for assessing the pavement surface, base, and sub-base layer thicknesses are needed. Ground-penetrating radar (GPR) has shown some promise in this area. The US Army Engineer Research and Development Center (ERDC) has completed a Small Business Innovative Research (SBIR) project with Pulse Radar, Inc., to develop a GPR system for airfield/road pavements. The system currently under evaluation at ERDC consists of multiple antennas with frequencies ranging from 100 MHz to1 GHz. This paper will describe the Pulse Radar system in detail, show data acquired with the system, and discuss the accuracy of the system.

Designs of Automated Pavement Surface Distress Survey System

2019-08-03T09:29:17+00:00

This paper describes a novel design of survey system to collect pavement surface distress. The system includes four modules. They are artificial illumination module, image acquisition module, sync control module, data storage and analysis module. The system can carry out crack surveys at a nominal speed of 72km/h with full coverage of pavement surface. Crack recognition is performed offline. The prototype has been tested in laboratory conditions and completed a survey of about 15,000km real road at normal running speed (72km/h) between the year of 2003 and 2004.

Comparison between France and Quebec backanalysis methods of deflection measurements

2019-08-03T09:29:17+00:00

The Laboratoire Central des Ponts et Chaussées (France) and the Ministère des Transports du Québec (Canada) have developed a joint research project on the behavior of
roadways during severe frost conditions. This project aims to increase understanding about fatigue damage and their diminished load-bearing capacity under the combined effect of
traffic and frost-thaw cycles.
An experimental pavement was built in Quebec in 1998 and its behav ior was monitored for six years. Pavements with a cement-treated base and a hot-mix asphalt base were selected.
Two test beds of each type were constructed. One of each two test beds was thermally insulated by a layer of extruded polystyrene, to d istinguish traffic and climate effects.
This paper compares France and Quebec backanalysis methods of deflection measurements of the two uninsulated test beds. It describes :
- the experimental site (pavement structures, weather conditions and surveys),
- the surface deformability measurements with a Benkelman test truck (inclinometer) for the LCPC and FWD for the MTQ
- the determination of moduli values by backanalysis of deflection measurements on test beds 1 and 4, and the differences and the difficulties met with French and Quebec methods.

How to Assess Elastic Properties of Heterogeneous Pavement Layers

2019-08-03T09:29:17+00:00

Backcalculation of elastic moduli is a common mechanistic approach for pavement overlay design. The method contains a model for assessing stresses and strains in various parts of the structure predicting the bearing capacity and future expected life. The precomputer era model was based on a single surface deflection only, which could be elaborated to various states of the loading, temperature and materials. Today, most pavement engineers analyze the shape of a deflection basin, allowing for a 3-dimensional view of the structure. Thus, we assess different elastic properties for a number of layers in the structure. By changing the nature of the load by magnitude or duration we can also derive non-linear properties often by using finite element modeling. However, if too many properties are being solved at the same time, there are two drawbacks. One is the long computational time being required, the other is that solutions may not be robust. So many pavement engineers use e.g. a standard load, a standard temperature et cetera. Unfortunately, in such cases it is difficult to use heterogeneous layers in the model, like coating and penetration binders. It has been suggested that such layers are treated as two separate ones, but one of their key functional roles of eliminating sliding interfaces is then being forfeited. The present paper suggests a guide to assess appropriate elastic moduli, as well as layer thickness and layer interface friction that could be used for linear elastic analyses.

Including Bearing Capacity into a Pavement Management System

2019-08-03T09:29:17+00:00

Since three years the Province of Milano is conducting performance surveys of the road network. The survey includes roughness (IRI by ARAN), distress (percentages of cracked and ravelled area, potholes), friction (SFC at 60 km/h by SCRIM) and bearing capacity (deflection by FWD). The purpose of the work is to set up, with the support of the Technical University (Politecnico) of Milano, a specific Pavement Management System (PMS) for the main road network of Province of Milano (covering a total length of 120 km with high AADT values and heavy traffic percentages). The PMS developed two years ago is already used to support technical decisions concerning planning of maintenance works, the evaluation of budgets according to expected performance levels etc. The first implementation included only three of the indexes surveyed: SFC60 km/h, IRI and percentage of cracked area. After completion of the survey concerning bearing capacity of the pavement over a wide part of the network also this parameter is being included into the PMS. Currently, bearing capacity data are available almost network-wide and the criteria used in the implementation of the bearing capacity in the PMS have been defined. The paper presents the data on the distribution of bearing capacity conditions over the surveyed network and shows how the
influence of bearing capacity has been taken into account in the latest modification of the PMS developed for the main network of Province of Milano. The experience may be of particular interest for other Administrations facing the development of a PMS.

Unbound Material Resilient Behavior due to Post Compaction –A study Comparing FWD and Tri-axial Tests

2019-08-03T09:29:17+00:00

Researchers have investigated deformation properties in unbound road materials for many years. Both laboratory tests and field measurements have been used and models have been developed. In the summer of 2003 a field test were carried out in the vicinity of town Uddevalla 90 km north of Gothenburg, Sweden. At the site, eight test cells were constructed, with different types of unbound layers. Four of the test cells were constructed with different material properties in the base layer and four of them with different base layer design on light fill material. A Heavy Vehicle Simulator test was carried out on all test cells. Other activities like a Falling Weight Deflectometer test were done prior to and after the accelerated loading test Laboratory tests like tri-axial were performed as well. Evaluation of stress sensitivity by using K-㮀 model shows an increase in stress dependent deformation behavior after permanent deformation occurred. These results are confirmed both from Falling Weight Deflectometer and tri-axial results. The relationship between the level of stress sensitivity and post compaction (permanent deformation) is evaluated and the same tendencies can be seen using either laboratory tri-axial tests or field testing. Thus, there is a potential for analyzing Falling Weight Deflectometer data at different load levels for predicting future rutting in unbound materials.

Correction Problem of Pavement Evaluation with FWD Deflection

2019-08-03T09:29:17+00:00

The asphalt pavement with bounded base works linear elastically under FWD impact load 40～60kN. Different pavement has different contact pressure even though the same height of FWD falling weight, and the difference can be more than 10% at the center of the load plate. The regressive relation between the deflections under standard (50KN) and the other load was established. The statistic formula was also given for the transfer between FWD and Benkelman Beam deflection in Jilin province.

Applicability of Static and Dynamic Analytical Methods to Structural Evaluation of Flexible Pavements Using FWD Data

2019-08-03T09:29:17+00:00

We have two methods to evaluate pavement structures by back-calculation based on linear elastic theory using Falling Weight Deflectometer (FWD) data. One is the multi-layer elastic method (static method), in which the peak load and peak surface deflections at sensors extracted from time-historical FWD data are utilized. The other is the dynamic FEM (dynamic method) directly using the time-historical FWD data for analysis. In this study, back-calculations of layer elastic moduli for the structural evaluation were conducted by static and dynamic methods on FWD data at a flexible pavement, which Transportation Research Board (TRB) has uploaded on the website. At the same time, Dynamic Cone Penetorometer (DCP) and Multi-Depth Deflectometer (MDD) were also performed besides FWD test. The modulus of base layer back-calculated by static and dynamic methods is in good agreement with those estimated by DCP. The modulus of subgrade back-calculated by static method was slightly less than that back-calculated by dynamic method or estimated by DCP. On the other hand, the internal displacements calculated by both static and dynamic methods with back-calculated layer modulus were consistent with the measured results by MDD. Therefore, it was demonstrated that both static and dynamic methods would be applicable to predict the pavement response (displacements) in adequate accuracy

Material and Structural Interpretation of Dynamic Response Data

2019-08-03T09:29:17+00:00

Load response data collected with the foundation layers to pavements using the light weight deflectometer have been plotted by frequiency and by spacial location. The plots show that the light weight deflectometer is sensitive to aggregate grading and packing and a meaningful interpreation of the data can enable a prediction of the surface deflection pattern with a complete pavement . and can be used to certify foundation layers with a pavement. Using the dynamic surface modulus of grunular materials alyers and soill foundation and the dynamic stfiffness modulus of asphalt layers a "long-life" deflection signature with a flexible pavement construction can be made.

Dynamic Investigation of Pavements

2019-08-03T09:29:17+00:00

The design of pavement structures is usually carried out under the assumption of bonded interfaces between the various layers. However, interface defects exist leading to a different stress diagram, which reduces the bearing capacity of the roadway. Mechanical impacts in a broad range of frequencies, give different responses according to the presence or the absence of defect. According to the intensity and the frequency of the impact, the physical phenomena differ, leading to different measurement and data processing. The paper presents different experiments using impacts on test sites, and compares the practice of these methods. It illustrates the problem of the coupling between the sensor and pavement surface to sound. It also compares the results of the method in different frequencies ranges.

Modelling of Pavement Response From a Field Test

2019-08-03T09:29:17+00:00

Modelling of pavement response is central in mechanistic pavement analysis and the validity of response models is hence an important prerequisite for reliable evaluation of structural pavement condition. With the objective of verifying predicted pavement response, an instrumented field test pavement was established on top of a sandy material sufficiently thick to be considered a halfspace. Later a layered flexible pavement system was constructed on top of the halfspace. Falling Weight Deflectometer (FWD) loads were applied at each layer of the pavement to provide input to built-in instruments, which registered stress and strain in three orthogonal directions in the sandy subgrade. At each pavement layer additional FWD measurements were carried out at several locations to determine elastic layer moduli. Based on layer moduli, pavement response was predicted using response methods ranging from a simple Boussinesq mod el to finite element methods. Comparison between the predicted and observed pavement response showed very good agreement for strain response
while the agreement was more questionable for stress. The paper shows that although it was difficult to establish a completely homogeneous test field, several response models reliably predicted strain response in a halfspace, while a three-dimensional finite element program considering the dynamic load situation performed best in the prediction of response in a multilayer pavement system.

Network and Project Bearing Capacity Surveys and Analyses Using Modern Techniques

2019-08-03T09:29:17+00:00

In recent years bearing capacity surveys in the Swedish Road Regions Mitt and Melardalen have been performed on network and project level using integrated analyses of modern road survey techniques. The survey methods include:
· Digital video capture
· Measurements of the structure with ground penetration radar
· Measurement of the bearing capacity using falling weight deflectometer
· Sampling and laboratory testing
· Visual inspection of the drainage
· Visual inspection of the road surface condition and damages
· Measurements of the road surface condition with laser profilometer.

The results of the measurements are assembled, linked together, processed and analysed using Road Doctor™ for Windows software. The results can be shown on the computer screen as a continuous longitudinal profile for each project. All data are linked to the right length position. For each project, rehabilitation measures can then be optimised for each location. Thereby the design work is facilitated and the resource use and the costs for maintenance and/or rehabilitation can be reduced.
This technology was used in a 5-year bearing capacity survey project in Road Region Mitt of the Swedish National Road Administration for the years 1998-2002. The total length of the road network surveyed was about 5 000 km. The condition of the road structure and the road surface are shown for each project in continuous longitudinal profiles and on GIS-maps as 500 m average values. Road surface roughness, measured as IRI, and rutting values have been used to calculate the remaining lifetime for each 500 m of the surveyed paved road projects. The remaining lifetimes, depending on roughness and rutting as well as the bearing capacity condition, are shown on the GIS-maps. For gravel roads the bearing capacity described in three different ways is illustrated in the same way. These maps can be used for planning and
selection of maintenance and/or rehabilitation candidates.

MECHANICAL BEHAVIOR OF INSULATED PAVEMENTS

2019-08-03T09:29:17+00:00

Pavement insulation is a widely accepted technique for the mitigation of frost effects on pavements. Many of studies were carried out on the mechanical implications of using insulation materials; however most of them deal with lightweight fill and rarely with insulated pavement. As a consequence, little information is available on insulated pavement mechanical behavior. A test track, including three 150 meter sections, was built in southern Québec, Canada. One section is insulated with extruded polystyrene, another with saw dust and the last one is a non-insulated reference section. All sections are instrumented in order to monitor frost depth and frost heave and to measure the mechanical response under standard load with a deflectometer. This paper presents an assessment of the pavement mechanical behavior in relationship with its long-term condition. The long-term performance of the test sections is analyzed with considerations for frost protection advantages versus possible disadvantages due to insulation material low strength. The main conclusion of this experimental study is that if thermal and mechanical efficiency of extruded polystyrene used as an insulation material in pavement is clearly demonstrated for almost all kinds of traffic loads, it is much different for saw dust. In fact, saw dust used as an insulation material in pavement causes a significant loss of bearing capacity which leads to a limitation of traffic loads even though it shows a good thermal performance.

Unbound crushed concrete in high volume roads

2019-08-03T09:29:18+00:00

In Norway, recycled concrete aggregate has recently been introduced in design codes for road construction, including material specifications. A number of field projects have revealed good functional properties (proven suitability), despite the fact that the mechanical properties of the materials in many cases do not comply with specifications concerning mechanical strength. Many traditional test methods for mechanical properties are clearly not suitable for this kind of materials. A proper evaluation should therefore be based on performance-related (functional) tests. The paper discusses these field-lab contradictions with reference to a field trial at highway E6 south of Trondheim. There crushed concrete is used as sub-base layer in a pavement designed for rather heavy traffic (ADT > 10000). Several field and laboratory tests have been conducted before, during and after construction, and the paper is focusing on comparing field tests with both empirical (old) and functional (new) laboratory tests, including a large-scale cyclic triaxial test apparatus. The road was constructed 2003-2004, and will be followed up by frequent bearing capacity (FWD), rutting and evenness (IRI) measurements. These data and results, both from field and laboratory investigations, will give valuable inputs to new Norwegian pavement design standards. This should encourage further use of recycled/secondary materials.

Characterisation of Cementitiously Stabilised Pavement Materials

2019-08-03T09:29:18+00:00

Cementitious stabilisation of pavement materials has a long history of use in Australia and other countries. Since its first recorded attempts in the 1940s, stabilisation has been further developed and now a wide range of binder options exist. The Australian Accelerated Load Facility (ALF) program has allowed advancement of stabilisation material assessment in the field, whilst layered elastic analysis has allowed these materials to be directly considered in pavement thickness design. These circumstances have lead to the desire to improve the laboratory characterisation of these materials. Australian practice has moved towards the use of Indirect Diametrical Tensile testing for strength, modulus and fatigue life determination, using samples prepared by gyratory compaction methods. The development of generic relationships between strength, modulus and fatigue life, which are able to be customised to specific materials by a simple and timely test, are now being investigated.

Sulfate Attack on Stabilized and Recycled Materials in Pavements

2019-08-03T09:29:18+00:00

There have been several instances of sulfate attack on portland-cement- and lime-stabilized materials and on recycled portland-cement concrete used in pavements at US Air Force (USAF) airfields. While the chemical reactions are similar to those found in
conventional sulfate attack on portland-cement concrete, the nature of the attack in a pavement setting makes conventional methods for protecting portland-cement concrete from sulfate attack ineffective for these stabilized and recycled materials. This paper will review the nature of the failures encountered on these USAF facilities. These examples show that even use of Type V sulfate-resistant cements proved inadequate to prevent attack. The paper will conclude with a discussion of our current shortfalls in knowledge and guidance in this area.

Characterization of the Behavior of Granular Road Material Containing Glass Cullet

2019-08-03T09:29:18+00:00

Granular base layers in highway pavements use large quantities of aggregate materials and are therefore good applications for possible use of waste materials such as glass. The engineering suitability of glass cullet as a granular embankment material is well documented. This paper presents results from resilient modulus tests on a blend of caliche, which is a conventional granular material used in pavement subbase layers, and glass cullet. Resilient modulus of granular material depends on factors such as aggregate mineralogy, particle characteristics, density, moisture content and gradation. However, when a material blend is used, the material response appears to also depend on relat ive strengths and compatibility of constituent materials in the blend. The general acceptance has been that by blending glass cullet with conventional materials, its engineering properties, particularly the strength, decreases. However, results from resilient modulus tests indicate that for relatively weaker granular base materials such as caliche, the introduction of glass cullet increases the strength of material blend. However, the strength gain appears to be accompanied by a likelihood of the material to fail by dilation at higher stress levels. As long as the calicheglass
cullet blend is not subjected to excessive loading, the presence of cullet in the blend appears to strengthen the resilient properties of the granular material.

Use of Reclaimed Asphalt Pavement (RAP) in Malaysian Hot Mix Asphalt (HMA)

2019-08-03T09:29:18+00:00

Recycling technology for advanced pavement materials has been realistically proven to be more economical, energy- saving and substitute materials to traditional ones. In making the recycled premix, asphalt surfacing reclaimed from old flexible pavement are reprocessed along with some virgin materials to produce modified asphalt mixes. They may be placed on the same roadbeds from which the reclaimed asphalt pavements (RAP) came but their uses can be applied herever the needs dictate. Recycled premixes vary widely in their contents of RAP, virgin aggregates, fresh asphalt and recycling agents that much react as additives or fibre or filler. A state of Selangor road improvement projects was selected as an initial study. The first step is to establish the probable causes of pavement distresses. Towards the end, the original pavement design and construction records are rigorously reviewed. The usual laboratory tests are carried out to test the physical and structural properties of the RAP. Moreover, the aggregates and the ageing asphalt that form the RAP have specific characteristics that definitely must be separately evaluated. RAP may range from as little as10 percent to as much as 70 percent of the final mixtures. These asphalt paving mixtures with certain amount of RAP requires standard testing in addition to the common Marshall procedures. The considerable composition of RAP that is applicable in asphalt mix must be obtained. Such standard testing are aggregate gradation, typical aggregate and asphalt tests plus the performance analysis.

Dynamic and Creep Properties of Binders Modified with Waste Tyre Rubber

2019-08-03T09:29:18+00:00

A dynamic shear rheometer was used to investigate the effect of Crumb Rubber Modifier (CRM) from used tyres on the dynamic and creep properties of bituminous binders. Modified binders were produced by blending CRM from two different origins, car and truck tyre, with bitumen under different conditions of time and temperature using a high shear mixer. Rubber-bitumen composites are considered heterogeneous (2-phase) systems of rubber particles dispersed within a bitumen matrix. Absorption of bitumen components by the rubber (swelling) inevitably depletes the bitumen of the absorbed components and modifies the properties of both the rubber and the bitumen phase. To assess the consequences, changes in dynamic properties of the composite material as well as those of the bitumen phase were investigated. Furthermore, a technique was developed to separate the two phases by filtering through a polyester cloth. Dynamic tests showed that CRM increases the stiffness and reduces the phase angle of the composite material but the extent of these changes is affected by mixing (interaction) time and temperature. They also indicated that the bitumen phase had increased stiffness and lower phase angle. The evolution of these properties with mixing time at 180 0C, however, followed the same pattern as the unmodified bitumen, which aged when heated at this temperature. Creep tests also confirmed that creep and creep recovery properties
of rubber-modified binders are affected by the origin of the rubber as well as by the mixing conditions.

Performance-based optimization of tire rubber modified asphalt mixtures

2019-08-03T09:29:18+00:00

A quantity of approximately 45.000 tons of waste tires is burnt in incineration plants in Austria per year. New recycling technologies enable the production of high quality rubber and fiber products from recycled car tires. One field of application may be the use of recovered fibers and rubber products for the modification of asphalt mixtures for road pavements. Successful use of rubber modifications of asphalt mixtures is reported in literature, but no sufficient information is provided on a systematic approach for mix design of rubber modified asphalts based on performance oriented test methods. This paper deals with this question, and reports of an on-going research project, where a new type of fiber and/or rubber modified stone mastic asphalt (SMA) is developed on the basis of a systematic performance-based test procedure. Both, bitumen and asphalt performance are considered. At first, rheological binder tests, i.e. Bending Beam (BBT), Dynamic Shear Rheometer (DSR) and Rotational Viscosimeter (RV), are used to optimize the performance properties of the rubber modified binder. The rubber modification of the binder was done in the laboratory as wet process. Consequently, laboratory specimens of rubber modified asphalt mixture are exposed to performance-based tests, i.e. the Tensile-Stress-Restrained-Specimen-Test, the Uniaxial-Stress-Test, the Triaxial-Stress-Test, and the Nottingham-Asphalt-Test. Here also the dry process was investigated, where specially granulated rubber is mixed with the hot minerals before the bitumen is added. By means of these test methods, a prediction of the inservice performance of the asphalt mixture is possible, in regard to the low-temperature behavior, the stiffness properties, and the resistance to rutting. In a further step it will be analyzed, if the new asphalt mixture is a technically equivalent alternative, but economically favorable to conventional techniques.

Behavior of Lime-Treated Cold In-Place Recycled Asphalt Pavements

2019-08-03T09:29:18+00:00

Use of recycled materials has great potential for rehabilitation of low to medium volume roads effectively and inexp ensively. However, cold in-place recycling (CIR) technology lacks performance data and field demonstration projects. In this study, the design and performance characteristics of the CIR materials from two sites namely, Salina and Osborne sites in Kansas are determined in the laboratory. The laboratory tests include physical property (e.g., moisture, gradation, air voids, and emulsion) and performance-related (e.g., resistance to deformation, and rutting) testing. Relative performances of the CIR mixes from these two sites are then analyzed. Results show that the CIR mixes from both Salina and Osborne sites exhibited good resistance to deformation, and other criteria for low to medium volume roads. Addition of lime slurry into a milling-emulsion mix caused a significant improvement in the dry and wet rutting. Samples with 2.5% Reflex emulsion and 4.0% lime slurry additive used in the Salina site exhibited lower rut depths compared to the samples with 2.0% Reflex emulsion and 2.5% lime slurry additive used in the Osborne site. The resistance to deformation values varied only slightly between the initial cured and fully cured samples,
indicating that R-values may not be a suitable property or indicator of the quality of a mix. It is believed that the data and results presented in this study will be useful in implementing the CIR technology for pavement rehabilitation.

Laboratory and field tests with stabilisation of a base layer using inplace milling

2019-08-03T09:29:18+00:00

Stabilisation of base layers using in place milling and foam bitumen is a very cost efficient method for rehabilitation of worn asphalt surfaced road and upgrading of gravel roads to paved surface. This method has been used successfully in Norway using mostly 3 - 5 % foam bitumen [Skoglund and Bakløkk, 2002]. To investigate use of less amounts of bitumen and an alternative stabilisation agent a field test was established. In connection to the field test extensive laboratory testing was performed. All the test sections has so far performed very well and no significant damages or differences between the test sections could be observed. The laboratory tests show that all the stabilised samples get a high increase in resistance against permanent deformations. The samples stabilised with 2 % bitumen was not significantly weaker than the ones stabilised with 4 %. The samples stabilised with DUSTEX showed a very high increase in both resilient modulus and resistance against permanent deformations after curing. However, more research is needed to verify the durability of this method of stabilisation, especially for use when the material is exposed to frost or high degree
of saturation. (Støtterud and Dahlen, 2002)

MnROAD’s Future Vision

2019-08-03T09:29:18+00:00

Minnesota Department of Transportation constructed the Minnesota Road Research Project (MnROAD) between 1990-1994. This paper reviews MnROAD’s existing resources, seven key research topics, current test cells avalible for reconstruction, and the expected actions needed to accomplish the key topics for MnROAD’s next phase. The MnROAD site is located 40 miles northwest of Minneapo lis/St. Paul and is an extensive pavement research facility consisting of two separate roadway segments containing 51 500-footlong distinct test cells. The 3 ½-mile Mainline Test Roadway (Mainline) is part of westbound interstate 94 and contains 31 test cells and carries an average of 20,000 vehicles daily. Parallel and adjacent to the Mainline is a Low Volume Roadway that is a 2 ½-mile-closed loop that contains the remaining 19 test cells. Traffic on the LVR is restricted to an MnROAD op erated 18 wheel, 5-axle, tractor/trailer with two different loading configurations of 102kips and 80kips. Subgrade, aggregate base, and surface materials, as well as geometric design methods vary from cell to cell. Daily information is gathered via a computerized data collection system that monitors more than 4500 mechanical and environmental sensors.

Analysis of CC2 Rigid Pavement Test Data From the FAA’s National Airport Pavement Test Facility

2019-08-03T09:29:18+00:00

The Federal Aviation Administration (FAA) conducted full-scale traffic tests on new rigid pavement test items at the National Airport Pavement Test Facility (NAPTF). Construction Cycle 2 (CC2) consisted of three independent rigid test pavements on mediumstrength subgrade as well as a smaller test strip constructed on low-strength subgrade. Trafficking of the three CC2 test items began in April 2004 and was completed in December 2004. Tests were conducted using four- and six-wheel simulated aircraft gear loads and were designed to compare three different support systems: conventional (aggregate) subbase, stabilized (econocrete) subbase, and slab-on-grade. This series of tests yielded significant data on the performance of rigid pavements constructed to current airport standards. This paper summarizes the trafficking data obtained from CC2 tests and presents an analysis of the relation between gear coverages and pavement performance, making use of the structural condition index (SCI) concept. The performance of the test items was compared to the rigid
pavement deterioration model used in the FAA’s LEDFAA design procedure. Preliminary design factors for all tests were evaluated using a three-dimensional finite element response model as implemented in the FAA’s beta design computer program (FEDFAA). The results of these full-scale tests, supplemented by available data from historical full-scale tests conducted by the U. S. Army Corps of Engineers, will be incorporated into the updated performance/ failure models in the FAA’s new design procedures for rigid pavements planned for 2006.

Determination of Rutting and Water Susceptibility of Selected Pavement Materials using MMLS3

2019-08-03T09:29:19+00:00

Accelerated pavement testing (APT) has become an increasingly important research tool to evaluate and validate pavement materials. Model APT devices, such as MMLS3, which can be used in situ and in the laboratory, have been used very successfully for this purpose recently. This paper describes the results of testing 48 cores from different Swiss pavement structures (hot and cold thin surfacings, porous asphalt, gussasphalt and stone mastic asphalt SMA) using the MMLS3 load simulator. The research was conducted at Stellenbosch University where the MMLS3 test set-up has been modified to provide the ability for accelerated pavement tests on cylindrical asphalt specimens. Furthermore, the test set-up enables the study of the susceptibility to water damage of an asphalt structure. The aim of the investigation presented in this paper, was the comparison of dry and wet asphalt pavement materials in order to determine their susceptibility to rutting.
First results clearly indicate that the influence of water may reduce the performance of asphalt structures. In one case an increase of rutting up to 50% compared to dry testing was found.

Alligator Cracking on Bibi New Test Road and Fatigue Test Results for Asphalt Mixtures in the Laboratory

2019-08-03T09:29:19+00:00

This study describes fatigue failure characteristics of asphalt mixture and asphalt-layer design. We conducted long-term performance measurements on Bibi New Test Road and a four-point bending fatigue test in the lab. The test road was constructed in 1990 as part of National Highway 36 in Hokkaido, Japan. The test road consists of eight sections with a different total thickness of asphalt-layer and a different asphalt mixture at the bottom asphalt layer. It was subjected to a daily average of 2,441 repetitions of a 49-kN equivalent wheel load. Alligator cracking first appeared in 2001. The study and its results follow.
1) Fatigue cracking was observed on the four sections whose bottom asphalt layer is of coarse-graded asphalt concrete Type B(poor asphalt type). Fatigue cracking did not appear in
the sections whose total asphalt-layer thickness was the same as the sections with cracking but whose bottom asphalt layer was coarse-graded asphalt concrete Type A (normal type) or
dense-graded asphalt concrete, which demonstrates that cracking resistance differs according to the fatigue failure characteristics of mixture used for the bottom layer of asphalt concrete.
2) The four-point bending fatigue test revealed that the number of loadings to reach fatigue failure of different asphalt mixtures differed by a statistically significant degree. The lab test
results agree well with the results observed at Bibi New Test Road.
3) To reduce life-cycle cost, the bottom asphalt layer must incorporate an asphalt mixture with a high fatigue-failure resistance.

Geosynthetics Limitations for Bearing Capacity Increase

2019-08-03T09:29:19+00:00

There are several ways of the geosynthetics functionality. Well-known mechanisms are functions of separating, filtrating, protecting and slope reinforcing. There are several publications describing the influence of geosynthetics on increasing the soft-soil bearing capacity. However, this geosynthetics functionality has not been explained satisfactorily in detail yet. The research presented here deals with clarifying the possible geosynthetics functionality. Six kinds of gesynthetics of world known producers were selected for the measurement. The measurement was carried out in the Geotechnical Laboratory Testing Field (GLTF), which is a facility constructed for full-scale geotechnical measurements. The results of static plate tests show that the contribution of the geosynthetics to the bearing capacity increase is very limited. A significant increase appears only in case of a very low bearing capacity subgrade covered by a 20cm thick subbase layer reinforced by some geosynthetics. After the static part of the experiment the GLTF was equipped with a cyclic loader to simulate real traffic loading and tests for the evaluation of possible bearing capacity increase due to geosynthetics usage were repeated.

European Co-operation in Accelerated Load Testing – COST 347

2019-08-03T09:29:19+00:00

Investment in road construction and maintenance in Europe is at a very high level and any improvement will significantly affect the overall benefit cost analysis. An important way of analysing road pavements or maintenance options before commencing the expensive process of road construction is accelerated load testing (ALT). Traditionally, most ALT research has been conducted through national programs, but a Pan-European approach would be more efficient with regard to investment as well as acceptance of results. Since 2000, 17 European countries have been involved in COST 347 ‘Improvements in Pavement Research with Accelerated Load Testing’ under the European Commission with the main objective to harmonise the efforts of the individual European countries. The harmonisation was aimed at securing more efficient use of the ALT facilities in Europe through sharing of results, common testing methods and joint projects. In addition to the European countries, representatives from North America, South Africa, Australia and New Zealand have played
active roles in COST 347 thus creating a world wide ALT network. The Final Report of COST 347 is now available and the results are impressive. The main result is a common code of good practice for the use of ALT, which ties together the results of the work in COST 347. The common code is seen as a major tool for improving European co-operation in ALT. Among the specific results from COST 347 are a catalogue of European ALT facilities, and a
database of European ALT research projects and reference literature. The use of ALT in connection with other types of pavement research like desk studies, computer modelling, laboratory studies and test roads is discussed and finally a catalogue of ideas for future ALT applications is presented.

Evaluation of Rutting Variations in FHWA Full-Scale Accelerated Pavement Testing

2019-08-03T09:29:19+00:00

The Federal Highway Administration (FHWA) has been conducting full-scale pavement tests using two Accelerated Loading Facility (ALF) machines for over 18 years. Due to the expense of full-scale pavement testing, most pavements were tested without replication. Variation in performance in replicate tests becomes a major concern when aging takes place in the asphalt pavements. In order to increase our confidence in full-scale testing results, replicate tests were conducted during rutting experiments in a recently completed Superpave validation study (1993-2001). This paper summarizes the results of replicate tests, which were conducted on 12 pavement test sites. Statistical tests were first performed on the rutting results in the replicate pavements. Asphalt aging effect on the rutting was discussed. The variation components were identified and accuracy curves were developed for all test pavements. Finally, the rutting variations among the different pavement layers were also evaluated.

Full-Scale Testing of Pavement Response by Use of Different Types of Strain Gauges

2019-08-03T09:29:19+00:00

From 2002 to 2004 the COST action 347 (European Co-operation in the field of Scientific and Technical Research) was organized under the title “Improvements in Pavement Research with Accelerated Load Testing”, including full-scale pavement tests at a number of European research laboratories. In Lausanne, Switzerland (EPFL) a test pavement of a fullyflexible type was constructed and equipped with strain gauges of different types usually in service in Europe. The loading-facility in Lausanne is an indoor test-pit where road structures can be repeatedly loaded by a linear heavy-pavement-rutting-tester. Within the ALT-program the loading conditions were controlled, comprising a variation of the pavement temperature, a variation of the loading parameters (axle load, tire type and tire pressure, loading speed) and an investigation of the lateral distribution of the responding strains with respect to the load axis. Longitudinal and transversal signals were recorded, that resulted from measurements on the different types of strain gauges and in two different depths: 40 mm and 220 mm from the pavement surface. As a result the shape and the order of magnitude of strains were found for different levels of observation and for defined loading conditions. This makes it possible to
comparatively analyse the functionality of the different types of strain gauges on the one hand, and, on the other hand, to derive important information on pavement response that may
be used in pavement modelling and performance prediction.

Variable Subbase Thickness Effects on Rutting Performance of NAPTF Flexible Pavements Subjected to MWHGL Traffic

2019-08-03T09:29:19+00:00

The reconstructed flexible pavement test sections at the National Airport Pavement Test Facility (NAPTF) consisted of similar Asphalt Concrete (AC) and granular base thicknesses, but variable granular subbase thicknesses. These sections were simultaneously trafficked by 6-wheel and 4-wheel landing gears. Rut depth measurements were made at frequent intervals. The development of rut depths under trafficking were characterized using the Power model and the Pavement Surface Rutting Rate (RR) model. For similar number of load repetitions, test sections with reduced subbase thicknesses yielded larger rut depths. The Power model coefficient “A” is helpful in quantifying the rutting potential and early-life rut depth development. The final rut depths varied between 4 to 8 inches. The NAPTF 1-inch surface upheaval failure criteria did not yield consistent rut depths. A functional failure criterion is suggested.

A review and reliability assessment of frost penetration models

2019-08-03T09:29:19+00:00

Frost penetration in pavements and subgrade can lead to frost heave and thaw weakening, and hence influences bearing capacity of roads during winter and spring thaw. Several models of frost penetration have been developed based on energy and mass (specifically, water) balances at the surface and within the pavement structure. This describes a review of frost penetration models used in pavement design. It also includes an overview of major field studies and their use to validate frost penetration models. This forms the basis for the reliability assessment of the models and their advantages and disadvantages for predicting frost penetration.

Evaluation of Three Frost Heave Models

2019-08-03T09:29:19+00:00

Simulating the water and ice content of the ground, with an emphasis on the capacity to bear traffic, is important for planning the use of existing roads. Of most interest is how weak the ground becomes during thaw and the length of time during which the ground is weakened. If a model accurately predicts frost heave and the locations of the ice lenses that form based on ground surface temperatures, it then is a good starting point for understanding the location of the moisture during thaw. For this reason, we evaluated and compared three frost heave models based on the results of laboratory soil freezing tests. Of the three frost heave models evaluated, the PC-Heave model and the Porosity Rate model accurately simulated the frost heave. FROST was less accurate than the other two models.

Finite Element Modeling of a Thawing Pavement Structure

2019-08-03T09:29:19+00:00

A material model for soft soil was developed to simulate the deformation behavior of a thawing soil under vehicle loading on paved and unpaved roads. Freeze–thaw action produces a loose, wet soil that deforms significantly under vehicle loads. The material
model represents a frost–susceptible fine sand, which was used in full-scale tests of paved and unpaved road sections in CRREL’s Frost Effects Research Facility (FERF). The material model was fine-tuned using triaxial test data and validated against direct shear test data. The material model was then used in a dynamic, three-dimensional finite element simulation of a paved road structure subjected to vehicle traffic by loading from a rolling wheel. This was used to understand the effects of thaw on the degradation of paved roads. These initial findings show that the pavement layer experiences maximum stress when the base layer is thawing. This supports observations that the majority of the rutting of a pavement system occurs during the thaw cycle.

Svalbard airport runway. Performance during a climate-warming scenario.

2019-08-03T09:29:19+00:00

Svalbard airport runway (N78°14’, E15°30’) is constructed on continuous permafrost near the main settlement in the Svalbard archipelago, Longyearbyen. Since its completion in 1975, the runway has experienced pavement unevenness mainly caused by thaw subsidence (and consequent frost heave) of the ice-rich soil layers in the embankment. A major reconstruction of the runway was carried out in 1989, including insulation of the most affected areas. However, the reconstruction has only been partly successful and the runway is subjected to constant re-pavement with high maintenance costs. A new reconstruction is planned for 2005/2006 to improve the runway. The arctic region is expected to experience a mean annual temperature increase of between +4 °C to +7 °C during the next century and this may have a substantial impact for structures on permafrost. In order to evaluate the thermal performance of the runway under a climate change scenario, a final element model has been used to evaluate the thermal changes in the ground due to climate change.

Revising the Method for Calculating the Subgrade Bearing Capacity of Paved Roads on Embankments during the Thaw Season

2019-08-03T09:29:19+00:00

In cold, snowy regions in Japan, subgrade bearing capacity (described by design CBR) has been calculated in consideration of a possible drop in the capacity during thawing periods. However, because the bottom of the subgrade of a pavement on embankment is at a relatively great distance from the groundwater level, it is assumed that groundwater supply to subgrade that causes freezing is unlikely to occur. Therefore it is estimated that the subgrade bearing capacity of pavements on a high embankment may not drop even during thawing periods. This study describes a design method for design CBR of pavements on embankments in consideration of embankments heights. By introducing design CBR values that correspond to various embankment heights, pavement can be designed in a more cost-effective way. The study found the following: 1) on embankments with a height of 6 m or more, thawing periods were found to have only a slight impact on the subgrade bearing capacity. The field CBR can be used directly as the design CBR, 2) on embankments with a height of 3 - 6 m, the bearing capacity was confirmed to have dropped during thawing periods. The field CBR should be multiplied by 0.77 to obtain the design CBR, 3) on embankments with a height of 3 m or less, as the subgrade bearing capacity showed significantly varying degrees of deterioration, freezinglthawing tests should be made before CBR tests are conducted to decide the appropriate multiplication factor.

Analysis of Seasonal Bearing Capacity Correlated to Pavement Deterioration in Cold Region

2019-08-03T09:29:20+00:00

The Laboratoire Central des Ponts et Chaussées (France) and the Ministère des Transports du Québec (Canada) have developed a joint research project on the behaviour of pavements in a cold region. This project aims to increase understanding about fatigue damage of pavements under the combined effect of traffic and a decrease in bearing capacity during the thawing period. An experimental site was constructed in Quebec in 1998 and its behaviour was monitored for six years. Pavements with a cement-treated base and a hot-mix asphalt base were selected. Two test beds of each type were constructed. One of these two test beds was thermally insulated by a layer of extruded polystyrene, while the second was not, so that the researchers could distinguish between traffic and climate effects. This paper presents the analysis of the seasonal variation of bearing capacity related to deflection, subgrade modulus and tensile strain. Also, an analysis of the results describes the difference observed between the quasi-static and dynamic responses and the relationships between traffic loading and pavement performance.

IMPROVEMENT OF BALLASTED TRACKS USING SLEEPER PADS

2019-08-03T09:29:20+00:00

Despite the long history of conventional, ballasted railway superstructures further development is needed. The requirements like convenient deformation behaviour (settlements), low-priced maintenance and low noise emissions (air-born and structure born) have been boosted continuously especially for high speed applications. The track-settlement behaviour is influenced by the service conditions and the ballast pressure within the contact area between sleeper and ballast. The contact pressure can be reduced by increasing the contact area or by adding additional resilient components within the superstructure to activate greater load distribution by the rails. Qualified sleeper pads (USP under sleeper pads) give possible solutions. Measurements at field tests in Germany show a better track settlement behaviour. Furthermore additional resilient elements like sleeper pads have great influence on the dynamic vibration behaviour. The vibration velocities have been measured by special ballast stones equipped with accelerometers. Results concerning tracks with additional sleeper pads are available up to 160 km/h and have been compared with measurements performed on tracks with resilient rail pads. Requirements for sleeper pads are resistance against pressure
peaks by ballast stones, durable resilient properties, sufficient vibration behaviour and applicability for conventional construction and maintenance procedures. The experiences born
by laboratory tests and by test sections in revenue lines have been accounted for the new composed technical delivery conditions of the German Railways DB-AG for sleepers equipped with sleeper pads.

Revised requirements for stiffness of ballast mats in new Norwegian railway lines

2019-08-03T09:29:20+00:00

In the Oslo region new railway lines which include many and long tunnels below dwelling areas, now are constructed and planned. All the tunnel tracks are ballasted track. Ballast mats are the preferred remedial actions for reduction of ground
borne noise. In the paper the work which lead to revised requirements for ballast mats are presented. Ballast mats having a stiffness of Cdyn,3 Hz = 0.01 N/mm3 have been installed in the most critical sections of the new tunnels. The required thickness of ballast for this track is 550 mm between sleeper underside and ballast mat surface. In the paper the definition and measurement method for maximum structure borne noise levels are given. The paper also shortly presents the results of a social survey on annoyance from this kind of noise, the calculation methods for structure borne noise transmission, and a method for measuring the vibration transmission from the tunnels before the track is installed.

Bearing capacity development on low volume roads (a 15-year case study)

2019-08-03T09:29:20+00:00

This paper presents a 15-year study (1989-2004) of the actual bearing capacity development on a number of low volume road sections in Denmark. The project was started up in 1989 as part of the implementation of a PMS project and, apart from various deterioration technical aspects; the purpose was to study and uncover the actual bearing capacity development and to develop deterioration models for the bearing capacity of low volume roads in Denmark. The basis on which the mentioned test sections were selected will be mentioned in the paper as well as how they were divided into sections of 10x10 metres, how current and comprehensive analyses were made of materials and soil conditions. Furthermore, it will be discussed, how daily measurements and registrations were made of meteorological data, sounding of the groundwater level (which is high on some sections) and how an artificial lowering of the groundwater level influenced both negatively and positively on the road deterioration. Finally, results will be presented from selected sections where the bearing capacity has developed as expected, but in some cases also in a rather surprising way.

KEY WORDS: bearing capacity, PMS (Pavement Management System), FWD (Falling
Weight deflectometer), design, deterioration, distress, models, groundwater, condition; GPR
(Ground Penetration Radar), RoSy (RoSy Road Systems), residual life (based on Danish
design criteria).

Roller-compacted Concrete Pavements in Norway 20 Years Experience

2019-08-03T09:29:20+00:00

Roller-compacted concrete, as the name suggests, is concrete that in its unhardened state will support a roller while being compacted. During the period 1985 - 1995 a total of 68 km of concrete roads was constructed in Norway using this method, of which almost 60 km was in tunnels. The annual average daily traffic (AADT) on these stretches ranges from 200 to 10 000 vehicles per day, the majority having low traffic volumes. By 2005, almost 15 km of these concrete roads will have been paved over with asphalt. The remaining 53 km are located almost entirely in tunnels or on bridges. Experience indicates that:

• compressive strength should be greater than C45
• thickness of concrete wearing surface should be greater than 150 mm plus rut depth
• spacing between joints should not be greater than 6 - 8 m
• the full width of the road should be cast in one operation to avoid bad longitudinal joints
• only good quality aggregate with a max diameter of 22 mm should be used
• dust has been a problem in some tunnels during the first few years of operation
• quality of workmanship during casting has large implications for the final product
• annual measurements show very small increases in rut depth
• good maintenance and repair methods need to be further developed
• the performance of the concrete wearing surface is so good in some tunnels that it should last 50-100 years without any major maintenance

Evaluation and Rehabilitation of Composite Pavement on Motorway Network in Serbia

2019-08-03T09:29:20+00:00

In the eighties the pavements on motorway roads were built with the sub-base layer made with high strength of cement-treated aggregates. After a period of considerable fall of transit traffic and lack of maintenance ensued from the political isolation of the country, by the beginning of new century the transit traffic was returning on "arterial" road facilities in Serbia. This period was marked with extensive investments in road rehabilitation. It was required to prepare the model for pavement existing conditions assessment for about 450 km motorway network and planning of pavement maintenance within the short period. By measuring surface deflections with HWD Dynatest, and by having at hand reliable data on pavement structure, thus the basis was formed for creating the mechanical pavement model. After the analysis of pavement surface deflections, idealized models of future condition were established, so-called “pavement condition matrix”. That matrix includes three classes of foundation condition and six classes of pavement condition. Each homogenous section of the analyzed motorway network may be represented by one of models in “pavement condition matrix”. Those models define efective modules of particular layers (for calculation overlay), residual bearing capacity of relevant pavement layers, and other information, significant for calculation. A basis was made that way for calculation of overlay structure. A significant percentage of asphalt layers and cement-treated aggregates layers possess residual bearing capacity. That is the reason to design maintenance strategies through a concept of preventive maintenance for pavement structure within design period of 20 years in service.

NEW TECHNOLOGY OF SURFACE TREATMENT TARGETING TEMPERATURE REDUCTION OF ASPHALT PAVEMENT

2019-08-03T09:29:20+00:00

Reducing asphalt pavement temperature during summer season contributes to mitigate rut generation of the pavement effectively. New surface treatment materials which reflects both sunshine and infrared rays has been developed and applied on existing asphalt pavement surface. The rate of solar reflectance of the pavement is from 30 to 50 % depending on the color of the materials (black to gray). Measured surface temperature of the pavement applied with this type of surface treatment is by utmost 20 degree K lower than that of conventional asphalt pavement. Its maximum temperature reaches 60℃ and more during summer in Japan. The effect of temperature of the pavement is verified by showing a smaller rut depth generation in accelerated actual wheel load test. Rate of rut depth is approximately one third compared to conventional pavement. This surface treatment applied for pedestrian pavement offers comfortable feeling while walking. This result also brings to alleviate heat-island phenomena in urban growth area, where the rate of pavement area in large as about 20%. This paper presents outline of newly developed pavement technology which reduces surface temperature due to prevent pavement from absorbing solar radiation and its reflection properties. This paper also shows measured pavement temperature of some colored types, durability of the asphalt pavement with and without application of this surface treatment.

Factors Affecting Laboratory Rutting Evaluation of Airport Pavement Granular Layers

2019-08-03T09:29:20+00:00

This paper presents research findings on characterizing and predicting the permanent deformation behavior of airport pavement granular base/subbase layers constructed and tested at the National Airport Pavement Test Facility (NAPTF) in the United States. The P209/P154 aggregate materials were used in the construction and testing of the NAPTF flexible pavement test sections with variable thickness base and subbase courses. To account for the rutting performances of these substantially thick granular layers, a comprehensive set of repeated load triaxial tests were conducted in the laboratory on the P209 base and P154 subbase granular materials. Based on the laboratory test results, mathematical models were developed to predict maximum permanent deformations occurred under both 6-wheel and 4-wheel gear loadings applied following a wander pattern. The performances of the developed rutting models were evaluated for predicting the field accumulation of permanent deformations by properly taking into account the NAPTF trafficking data and the previous loading stress history effects. A comparison of the measured and predicted permanent deformations indicated that a good match for the measured rut magnitudes and the accumulation rates could be achieved only when the magnitudes and variations of stress states in the granular layers, number of load applications, gear load wander patterns, previous loading stress history effects, and trafficking speed or loading rate effects were properly accounted for in the laboratory testing and permanent deformation model development.

New Material Treatment Technologies in Management of the Effect of Seasonal Variations

2019-08-03T09:29:20+00:00

In the recent years, it has been considered more to use lower quality aggregates in road construction. This has become necessary mostly due to smaller supply of good quality materials available within a reasonable transportation distance and higher transportation costs. Nontraditional stabilisers have been marketed as economical and promising to improve the properties of poor quality materials. In the regions with long frost periods, such as S candinavia, open-graded aggregates containing a small amount of fines have been used in road construction in order to prevent frost heave. As fines content increases, the moisture susceptibility of aggregate becomes greater, leading to problems with bearing capacity in spring when frost thaws. The research was done to find out if non-traditional stabilisers would provide a toolbox for decreasing the moisture susceptibility of coarse-grained aggregates having, except for spring-time frost thawing, a sufficiently good bearing capacity. Polymeric and ionic stabilisers and resins have been tested. This paper presents the effects of the stabilisers on four different aggregates. The laboratory research consists mainly of Tube Suction tests. The literature studies and test results indicate that ionic and enzymatic stabilisers can hardly be used for decreasing moisture susceptibility in aggregates having a fines content of less than 15%. The tests showed that polymeric stabilisers and resins were the most promising stabilisers. It must be noted that the same stabiliser might act in a different way from one aggregate to another. Therefore it should always be checked whether the stabiliser is
applicable in connection with the aggregate in question.

The Study on Establishing the Pavement Performance Prediction by Artificial Neural Networks

2019-08-03T09:29:20+00:00

Measuring the condition of current pavement is accomplished by collecting field distress data and synthesizing data to identify appropriate alternatives for rehabilitation or reconstruction. Many agencies have pavement management systems (PMS) to assist with data collection, evaluation, and decision-making during this process. The present serviceability index (PSI) is a common tool for quantifying information concerning the serviceability of the pavement. A primary factor used in establishing the PSI is the roughness of the surface profile. The PSI can also include standard distress criteria such as rutting, fatigue cracking, and thermal cracking. However, the actual causes and conditions of pavement distress are very complex. The statistical modeling can only consider no more than a few of the parameters, in a simplified manner, and in some cases various transformations of the original data. Because of the statistical nature of models this does not mean that cracking and rutting are not important, since they will react on the roughness of the surface profile. The artificial neural networks (ANNs) offer a number of advantages over the traditional statistical methods, caused by their generalization, massive parallelism and ability to offer real time solutions. In this paper, real pavement condition and the subjective present serviceability rating (PSR) in Taiwan are used to develop a generic intelligent pavement performance prediction using ANNs. In contrast to statistical analysis, it is concluded that the good predictive results can be obtained from the pavement performance model established by neural network.

Structural Evaluation of a Pre-stressed Concrete Airport Pavement

2019-08-03T09:29:20+00:00

This paper concerns the assessment of the bearing capacity of a pre-stressed concrete airport pavement built in the 60’s, using non-destructive tests complemented with a number of other in-situ and laboratory tests aiming at the characterisation of the stress state in the concrete slab 40 years after construction. The work performed comprised visual inspection, FWD tests, core drilling and site investigation, “small flat jack” tests (normally used in rock mechanics), as well as the characterisation of the in situ stress condition of the pre-stressing wires. A finite element computer program was used, together with multi-layer computer programs, for modelling the pavement, taking into account different friction conditions at the interface between the concrete slab and the soil-cement sub-base. The paper describes the methodology used in the study and presents some of the results achieved.

Laboratory and Field Testings of the New Concrete Friction Sleeper

2019-08-03T09:29:21+00:00

In summer the temperature stresses in the rails may become very high and induce lateral distortion of the track with risk of derailment. In small radius curves (R < 300 m) there are restrictions on use of CWR due to the risk of track buckling. This requires fishplated rail-joints with their many drawbacks. To improve safety and reduce maintenance costs it was found essential to find a practical way of improving the lateral resistance of ballasted track with concrete sleepers. The new concrete Friction Sleeper was designed with cross-wise ridges at the under-side to form a coarse cogging with adequate dimensions to utilise more of the high internal friction potential of the crushed stone ballast. By lateral displacement of this sleeper a completely continuous layer of ballast material will be held fixed to the sleeper under-side by hooking, wedging and granular interlock, and give a very high friction resistance. In performed field tests the Friction Sleepers provided a considerably larger lateral displacement resistance than the standard concrete and wood sleepers. Based on the observation data in these tests, the track with Friction Sleepers obtained the highest absolute and relative lateral resistance values for all three axle load levels. A very important result was that the unloaded track with Friction Sleepers had a very high lateral resistance, 35 and 110 % higher than obtained by the track with the standard concrete and the wood sleepers respectively. Based on the field and laboratory test results the new concrete Friction Sleeper has a considerable potential to yield higher safety against rail buckling, increased use of CWR tracks and less strict requirements on ballast quality and ballast profile.

Application of Advance Pavement Technology for Airfield, Field Experience at Kuala Lumpur International Airport (KLIA)

2019-08-03T09:29:21+00:00

The basic requirement for civil engineering materials construction usage is to use and optimise readily available materials nearest to the work site. Dependency on imported technology can sometimes limit the application of good engineering materials. Working from first engineering principles supported by research is a productive method to use non-standard materials confidently under known local environment. The pavement works at the KLIA underwent thorough studies working from basic principles. These principles are fully deployed during planning, design and construction in line with the available materials. Advanced technology was adopted for the design and construction while new materials were introduced for construction. This paper describes the historical and technical development of the pavement studies under local conditions, design and construction at KLIA. The pavement used stabilize meta-sandstone base as a structural bearing layer. The surfacing layers comprises of the bituminous crack relief layer (CRL) overlaid by polymer-modified asphalt (PMA). All these layers were newly introduced and were applied for the first time in large quantities in Malaysia. After five years the technology used had shown the expected performance even though the loading condition increased. The incorporation of a pavement management system in the monitoring exercise is also described. Valuable lessons learned from the starting point of investment up to maintenance management stage is described to guide investors on optimum use of pavement technology to benefit all stakeholders.

Overlay Design in Mexican Roads

2019-08-03T09:29:21+00:00

The rehabilitation of roads is not a simple task. This process requires systematic techniques to evaluate the current state of the road as well as techniques to select the most plausible reinforcement works. This work describes the studies and evaluation process to rehabilitate a highway located in the east access of the city of Guadalajara, the second largest
city in Mexico. Particularly, the works focused on the left body of the Zapotlanejo- Guadalajara highway which experiences high volumes of heavy transit. The recycling technique was chosen to reinforce the highway. The recycling works uses recovered material in the formation of the hydraulic base as well as the material used in the asphalt surface of the new pavement. This paper describes the works performed before the rehabilitation works. These works include the results of the superficial evaluation, the structural analysis, the reinforcement design, the constructive procedure, and the performance studies covering ten years of successful operation of the highway.

Observations, Analysis, and Prediction of Asphalt Cracking

2019-08-03T09:29:21+00:00

The various causes/categories of pavement cracking and generalized criteria for identification of potential deficiencies are presented in conjunction with case histories that relate to investigations of pavement distress. Asphalt binder properties, such as viscosity and penetration are shown to relate well with thermal and combined thermal/load stress conditions. Although slightly more involved testing procedures are required, criteria have been developed for different yearly ESALS to identify a paving mixture’s resistance to top-down cracking. Dissipated creep strain energy parameters are obtained from indirect tension tests to define an energy ratio for separating cracked from uncracked pavements. It is difficult to interpret Falling Weight Deflectometer (FWD) data from cracked pavements unless special procedures are followed. At high pavement temperatures the influence of cracks will diminish and allow for improved determination of moduli for underlying pavement layers and foundation/ subgrade soils. These analyses are enhanced when asphalt viscosity relationships with resilient moduli are used to assign E1 values for backcalculation. Relationships or procedures for estimation of any pavement layer or subgrade modulus are very beneficial in simplifying the interpretation or backcalculation of other layer moduli. Where possible, laboratory test parameters that relate directly to the behavior of paving mixtures should be integrated in the design and performance models for asphalt pavements. Realistic, multiple/simplified, methods for design and/or evaluation of pavement performance are desirable over one specific approach since comparable results are an indication of reliability.

Development of a Hi-Soft Asphalt Pavement for Cold Regions

2019-08-03T09:29:21+00:00

Through structural evaluation and performance prediction, a new type of asphalt pavement was developed, based on 3 years of laboratory and in-situ tests. It is named a Hi-soft Asphalt Pavement, HIHSA in short due to its characteristics of being more flexible, and more adaptable to deformation and bearing capacity defects of the roads, etc. As the recent research findings from a research project financed by the Ministry of Communications, P.R. CHINA, HIHSA is more suitable for low volume roads in cold regions. During the development, the researchers highlights the use of local materials such as the naturally crushed stone accumulated in mountain slope, the river gravels and others, to the largest extent for wearing course, base-course and subgrade. And due to no need to heat at high temperatures for both aggregates and binders comparing with hot–mix asphalt, less low temperature cracking, easy recycling and maintenance, HIHSA is also very cost-effective. 11 different kinds of pavement materials and structures were chosen for the test road, which is located in the northern-most China’s Daxing-anling Region. According to in-situ observations and experiments on bearing capacity, frost heave, cracks and other defects, and others, in connection with lab tests and structural calculation and analysis, Specifications for HIHSA Pavements’ Design, Construction and Quality Control were worked out for further wide application in other northern and western provinces and areas.

Road Construction on Soft Soils in Indonesia: A Study on Soil- Pavement Interaction

2019-08-03T09:29:21+00:00

The soft soils area in Indonesia covers about 10 million hectares or 10 % of the total land area. Because of the low bearing capacity and high compressibility of the soft soils, many roads in this area lose their serviceability before the end of their original design life. One of the causes is that due to the lack of thorough understanding of the behaviour of the soil
and its influence on pavement performance, no optimum maintenance measures are carried out. This paper presents a case study of a road on a soft marine clay subsoil in Cilincing, North Jakarta, Indonesia. The road was built in 1980 and since that date many severe structural damages in the pavement occurred due to uneven settlement of the subsoil. To investigate the effects of uneven settlements on pavement response, the finite element method was utilized on a large scale in this study. From an extensive series of analyses, which included uneven settlements as well as traffic loadings, it can be concluded that an integrated soil/pavement analysis provides a much better understanding of the interaction mechanism between pavement and subsoil.

Study of a Rehabilitation Method with a Pavement Reinforcement System for Low Volume Roads

2019-08-03T09:29:21+00:00

This paper presents the first results of an experimental study aimed at evaluating the effectiveness of a rehabilitation method for low volume roads. The method suggests the usage of a steel reinforcing netting in order to improve the performance. It consist in reconstructing the surface layer placing a steel reinforcement in the interface between the new binder layer and the existing base course. This reinforcing method aims at making a road possibly support a sudden increase of number and load of vehicles quickly and with a modest maintenance. The research considered the problem from three points of view: real scale, by constructing and monitoring an experimental section; reduced scale, with laboratory tests reproducing the situations recorded in the experimental section; a finite element modeling using all the so gathered results. The findings show that although the steel netting is placed in the top layers of the pavement, it is still able to improve its resistance and its strain energy absorption ability consequent to the vehicles transit.

Permanent Deformation Behaviour of Low Volume Roads in the Northern Periphery Areas

2019-08-03T09:29:21+00:00

Roadex II has been an EU financed research project concentrating on the maintenance of the low volume road network in the Northern parts of Finland, Sweden, Norway and Scotland. One of the aims in the Roadex II project has been to assess the permanent deformation behaviour of the low volume roads in these Northern periphery areas especially for the purposes of finding efficient and cost-effective means of maintaining the structural condition of the road network with as little disruption as possible to the vital heavy transports of the forest and fishing industries and agriculture. This paper presents a tentative approach for estimating the risk of permanent deformations in a low volume road and the need for weight restrictions especially during the thawing period of seasonal frost. The assessment is based on a monotonic and repeated load triaxial test series performed at the Tampere University of Technology in Finland and at the University of Nottingham in the UK. The results of these tests have been interpreted using a non-linear finite element analysis to compute the likely plastic strain in the pavement and, hence, the risk of rut development, and a simplified approach proposed for routine use.

Results of a study on Environmental Practices and Regulations

2019-08-03T09:29:21+00:00

Growing interest in the environment in today’s society has led to increasing focus on environmental issues. This also applies to the road sector. By its very nature, this sector involves appreciable loading on the environment, so there is every reason to take active measures to achieve more environmentally appropriate operations. Appreciable gains can be made, environmentally as well as economically. The major environmental loading from the road sector originates principally from the exhaust gases and emissions from road traffic, although road building, rebuilding and maintenance of the road network also can cause significant environmental impact in certain cases. This paper is a part of the ROADEX II project.

Dealing with poor bearing capacity on low volume roads on peat in the Northern Periphery

2019-08-03T09:29:21+00:00

The Roadex II project is an EU funded trans-national technical co-operation between the northern European roads districts of Finland, Norway, Sweden and Scotland whose main aim is the sharing of technical information and good practice. The goal of subproject 2_5, ‘Dealing with Bearing Capacity Problems on Low Volume Roads Constructed on Peat’ was to gather together existing and past practices for dealing with bearing capacity problems for roads constructed on peat in the Partner roads districts, with particular reference to lightly trafficked roads. As part of this exercise interviews were held with practising roads and geotechnical engineers in the Partner areas to gain as full an insight as possible into their current thinking. The result of the research is a snapshot of the Partner area practices in dealing with bearing capacity problems in roads constructed over peat that covers such topics as the classification and engineering properties of peat, local field survey methods, testing, design considerations, risk management, methods of construction supplemented by local case studies. This paper gives a summary of the research carried out within the Partner areas and offers a ‘snapshot in time’ of local thinking for dealing with bearing capacity problems on low volume roads constructed on peat.

Socio-Economic Impacts of Road Conditions on Low Volume Roads

2019-08-03T09:29:21+00:00

Traditionally the road conditions on low volume roads have been neglected. The main reason is the economic resources, which are insufficient to cover all the needs. But there are also other reasons why the low volume roads are kept back in the road maintenance programs. Used socio-economic models to describe the maintenance need, normally deal with road user costs consisting of time delay costs, vehicle costs and accident costs. But as the amount of traffic always is the dominating figure in the calculations the models will favour a very good condition on high volume roads and only keep the low volume roads alive. That will give the highest benefits for the society with the existing models. To change this, in order to give people living in rural areas better life conditions, there is a need for a new thinking to find alternative ways to describe the significance in having good road conditions especially in the rural areas. The first thing is to look at socio-economic impact in a wider meaning. There is a need to take a closer look at the social improvements for people living in rural areas if the
road conditions are improved. Secondly there is a need to look at the health impacts, especially for professional drivers, if rural roads are left to deteriorate. By a literature survey,
meetings and interviews with skilled people from Sweden, Finland, Norway and Scotland it is found how the socio-economic impacts are considered today by the road managers and what
is going on for the future. The report will describe briefly the models used today, some
calculations done with a Swedish model, work done and going on to improve the road
conditions on low volume roads in the partner countries and in what way the road condition
may affect personal health for road users.

Monitoring and Classifying Spring Thaw Weakening on Low Volume Roads in Northern Periphery

2019-08-03T09:29:22+00:00

The ROADEX II Project is a co-operation aimed at developing ways for interactive and innovative management of low traffic volume roads in the Northern Periphery Area in Europe. The goal for subproject 2.3 “Spring Thaw Weakening” was to collect information regarding one of the most difficult challenges in low volume road condition management in cold climate areas, managing road condition during the spring thaw weakening period in a way that minimizes the impact of transportation problems on local livelihoods without destroying road structures or reducing the service level of the road for the rest of the year. The survey has followed the Roadex II Project phase II theme of “understanding and analysis” by using new technologies to monitor spring thaw problems and then analysing the problem sections so as to better understand the processes behind the problems. Data collection for monitoring the seasonal changes and spring thaw weakening was done at five test sites in Scotland, Sweden and Finland. This paper presents a summary of the field tests and, based on these results, proposes a new classification for spring thaw weakening periods and typical spring thaw damages that can happen during these periods. This helps engineers to better focus on the problems and find more economical and sustainable solutions in managing spring thaw problems in their low volume road networks.

Typical drainage problems in Northern Europe and the effect of improving drainage

2019-08-03T09:29:22+00:00

Typical drainage problems in the Northern Periphery area of Europe have been addressed in this paper. Field observations for roads on sloping ground shows large differences in rut depth and roughness on the road cut side compared to the embankment side. The road cut lane has the ground water table much closer to the road surface and therefore also a higher moisture content in the road structure materials and the subsoil. For 20 % of the analysed roads the rut depth on the road cut lane is 1.5 times larger than on the other lane. Just 12 % of the roads have larger rut depth on the embankment lane. Predictions models are used to demonstrate the change in lifetime (calculated as number of standard axles) as a function of moisture content. Both field observations and prediction models show that improving the drainage will give a large profit in lifetime and also the life cycle costs. These are calculated for a period of 50 years and the conclusion is that maintaining and improving the drainage system is cost effective and must be prioritised
among other maintenance activities. The first step in strengthening a road should be to make sure that the drainage system work properly and should be improved 1-2 years before paving.

On design principles of reinforced pavement structures - the COST 348 REIPAS action

2019-08-03T09:29:22+00:00

The paper is summarizing the development work for reinforcement of pavements and structures in the COST 348 REIPAS Action. Design approaches developed either for the utilization of geosynthetic reinforcement materials or for the utilization of steel grids are referred. The basic common principles of reinforcing practice is inserting or laying the steel or geosynthetics mesh below or underneath the pavement either during the maintenance or reconstruction of existing roads or construction of new sections. The COST 348 action is taking a step towards practicable guidelines for the structural design and execution of reinforced pavements and road sub-bases and to reach a consensus on the methods to determine relevant material parameters essential for analysing or predicting the behaviour of the reinforced structures.

Steel Grids, an Efficient Way to Improve the Durability of the Pavement

2019-08-03T09:29:22+00:00

A synthesis of the test results with steel grids in trial road constructions was made in the so called STEELSYNT project. The material for this synthesis has been: the TPPT (Pavement Structures Research Programme) test constructions, the European reinforcement research programme called Reflex and some HVS test projects. HVS (Heavy Vehicle Simulator) is a mobile accelerated loading test facility. All test results both in laboratory and in field conditions showed that rutting can be remarkably reduced by using steel grids in bitumen bound layers or unbound base. In average this reduction lies between 40 - 60 %. The reinforcement works best in the cases where the bearing capacity of the pavement is low. A steel grid prevents the development of longitudinal frost cracks in the reinforced area. The longitudinal cracks usually move to the edges of the road where the grid ends. Steel grid also mitigates the transverse frost cracking by curtailing the width of the cracks and by preventing the development of small cracks. The test results showed also that steel grid delayed fatigue to some extent. The Reflex project prognoses that reflection cracking of the cement bound gravel base can be reduced 35 % by steel grids. The studies so far have not found that longitudinal unevenness could be levelled with reinforcements. Falling Weight Deflectometer is not a suitable measurement tool to quantify the improved performance of a reinforced pavement, so new methods are needed.

EXPERIENCE FROM MORE THAN 30 YEARS OF ASPHALT REINFORCEMENT WITH POLYESTER GRIDS

2019-08-03T09:29:22+00:00

Reflective cracking is a well documented and known phenomenon. Without any treatment cracks and/or joints in existing cracked pavement structures will propagate nearly vertical through a new asphalt overlay, creating a reflective pattern similar to the one existing before. The prevention of reflective cracking in pavements has always been an area of concern when designing for asphalt concrete overlays. A very effective system for the delay or even complete arrest of reflective cracking has proven to be Asphalt Reinforcing Geogrids made out of Polyester fibres, which have successfully been used for about 35 years now.
Reinforcements have been successfully used in different applications as roads, highways and airports in nearly all climatic conditions. Examples of evaluations in various countries and conditions are given. Also a number of laboratory studies have been performed on reinforced asphalt systems. The goal of most studies was to simulate the actual load condition of a cracked pavement. When a wheel passes a crack the system is stressed dynamically in different modes (bending and shearing) depending on the wheel position. Additionally horizontal movements may occur due to temperature variations. The results of the studies will be summarised. Special attention is also given on the performance on site, such as the installation process, milling of reinforced asphalt and the reuse of recycled reinforced asphalt.

Steel Reinforced Asphalt Layers

2019-08-03T09:29:22+00:00

Due to the increase of heavy traffic loading and expenses for road maintenance and rehabilitation a continuous research and development work in the field of innovative pavement and material designs is needed. Aims of reinforcement structures used in asphalt roads are prolongation of service life by increasing bearing capacity and delaying plastic deformations or cracking respectively.
Within the 4th EU-framework the REFLEX-project “Reinforcement of flexible road structures with steel fabrics to prolong service life”, was focusing on benefits and further developments of reinforced asphalt layers using steel fabrics. Dependent on the load and environmental conditions within Europe the research group was focusing on bearing capacity and on resistance against thermal cracking (including frost heave) reflective cracking, plastic deformations and flow rutting. This paper shows the German investigations, results and experiences focusing on flow rutting and bearing capacity:
- Design of reinforced pavements supported by theoretical models (Multi-layer-theory, FEM) to check the performance of net structures.
- Interaction between asphalt and reinforcement structures (bond) as well as performance of reinforced layers by lab tests.
- Monitoring of the behaviour of steel reinforcements during the placing of the asphalt and establishment of recommendations for the design and the construction of such pavements. Measurements performed during the paving process show the sensitivity of this technology (especially for the usage against flow rutting) given by the fundamental material properties of asphalt and steel.
- Monitoring of test sections (especially bus-stops) and road sections.

Geosynthetic Material Properties for Use in 2-D Finite Element Pavement Response Models

2019-08-03T09:29:22+00:00

Modern finite element response models for flexible pavement analysis and design are traditionally two-dimensional axisymmetric models. The inclusion of a geosynthetic reinforcement layer in such a model is generally accomplished by the insertion of a horizontal layer of membrane elements. These elements are particularly well-suited for describing geosynthetics in that they carry loads in tension while having zero bending stiffness. The use of a 2-D axisymmetric response model requires that the reinforcement be described by an isotropic material model. Geosynthetics commonly have direction dependent properties, the most notable being an elastic modulus that differs between the machine and cross-machine directions of the material, which are described best by an orthotropic constitutive model. This paper presents an approach that allows a geosynthetic’s orthotropic linear elastic properties to be converted to equivalent isotropic linear elastic properties for use in 2-D finite element response models. This is accomplished through a work-energy equivalency equation developed from a general stress application to a geosynthetic material modeled by an orthotropic and an isotropic linear elastic sheet. Parameters contained within the equation are calibrated by the comparison of pavement response of a completely 3-D finite element model containing a geosynthetic having an orthotropic material model to a 2-D finite element model having an isotropic material model for the geosynthetic. The study results in a simple equation to convert orthotropic properties to equivalent isotropic properties.

Proceedings of the international conferences on the bearing capacity of roads, railways and airfields

Introduction to the conference

What Does an Aircraft Expect From the Pavement?

Modern Railways for Cargo and Passenger Traffic High Speed- Heavy Loads Track Systems

Impact of Heavy Vehicles on European Roads

Comparative Study of Laboratory Based Methodologies for Determination of the Resilient Performance of Clay Subgrades

Strong Correlation between the Bearing Capacity and CBR of a Gypsiferous Subgrade Soil Subjected to Long-Term Soaking

Prediction of stiffness of unbound granular materials based on the CBR value

Influence of Degree of Saturation on Bearing Capacity and Compaction of Glacial Till Embankments

A study on the influence of water and fines on the deformation properties of unbound aggregates

Influence of Suction on the Properties of two Granular Road Materials

A new material model for permanent deformations in pavements

A Laboratory Measurement of The Hydraulic Conductivity of Fragmented Gravels

The Routine Laboratory Assessment of the Performance of Coarse Granular Materials for Pavement Foundation Design

Prediction of permanent deformations of unbound pavement layers

Advanced Models for Predicting Aggregate Rutting Behavior

Evaluation of grain shape characterization methods for unbound aggregates

Evaluation of the effect of particle shape on the bearing capacity of railroad ballast with discontinuous analysis

Round robin investigation on the cyclic triaxial test for unbound granular materials

Characterisation of Some Candidate Surfacing Materials for Orthotropic Steel Bridge Decks

Linear viscoelastic properties of mastics: results from a new annular shearing rheometer, and modelling.

Computational Fluid Dynamic Modelling of the Rotational Viscometer

Comparison of the Zero Shear Viscosity of Bitumen-Filler Mastics Using Different Measurement Techniques

The New Method of Evaluation of Stress Relaxation Properties in Road Bitumens

Evaluation of a newly developed asphalt binder selection system for mix design

The Effect of Aging on the Rheology and Fatigue Response of Bitumen in Relation to Raveling in Porous Asphalt

Characterisation of Uniaxial Creep Deformation Behaviour of Asphalt Mixtures

A contribution to the modeling of permanent deformations of bituminous mixes

Asphalt Cold Mixtures for Pavement Rehabilitation: Curing and Mechanical Characteristics

Characterisation of Fatigue Damage of Asphaltic Materials

Prediction of thermal cracking resistance of some SBS modified binders and mixes

Evaluation of Indentation Test to Characterize Asphalt Concrete Mixtures in Pavements

Evaluation of Test Data Variability and Suitability of Predictive Equation Related to the Determination of Dynamic Modulus (E*) for Hot-Mix Asphalt

Evaluation of Temperature Associated Cracking in Asphalt Mixtures by Means of Performance-Based Laboratory Testing

Evaluation of Simulated Load Techniques for Determining the Internal Angle of Gyration for the Superpave Gyratory Compactor

Norwegian experiences and conclusions regarding Gyratory Compactors

Superposition principle to determine properties of bituminous mixtures in the time –temperature domain

Functional testing of asphalt mixes on field samples

Evaluation of the stiffness modulus of bituminous mixtures using laboratory tests (NAT) validate by field back-analysis

Simplified Testing Method for Evaluation of Asphalt Mixtures for their Susceptibility to Permanent Deformation

Prediction of Low Temperature Crack Spacing in Asphalt Pavements

Some Insight into the Mixture Design of Large-Stone Asphalt Mixture for Airport Pavement

Water susceptibility of asphalt mixtures: Testing the effect of adhesion agents on different binder/aggregate mixtures

Viability of using a bituminous sub-ballast layer on high-speed ballasted tracks

A Railway Track Deflection Model Based on Nonlinear Discrete Support

Dynamic Loads Caused By Freight Trains With Wheelset Loads of 250 kN

Potential Remediation of Rail Track Foundations in Poorly Drained Clay Sites with Native Vegetation.

Theoretical versus Measured Flexible Pavement Responses Under Dynamic Loading

3-Dimensional Finite Element Analysis of Cracking

3D Finite Element analysis of accelerated pavement test results from New Zealand’s CAPTIF Facility

How may the variation of traffic loading effect measured asphalt strains and calculated pavement service life?

Investigation of Classification Parameters and Assumptions for Rigid and Flexible Airfield Pavements

Calculation and Forecast of Settlement of widened embankment

A STUDY ON THE EFFECT OF FAILURE PROBABILITY OF DESIGN FATIGUE CURVE ON THE RELIABILITY OF CONCRETE PAVEMENT

Analytical Study on Evaluation of Subgrade Modulus Using Portable FWD

Long-term Evenness of Pavements with Respect to Soil Deformations

Probabilistic Forecasting Model of Pavement Performance Based on BP Neural Network

The PERS System for Modelling Pavements Performance Based on Incremental-Recursive Techniques

Semi-rigid Asphalt Pavement's Premature Failures on Chinese Motorway Network

Predicting the Resilient Modulus of Unbound Granular Materials by Neural Networks

Road Map to Develop Methodologies for Determining Remaining Pavement Service Life

Prediction of Deformation Behaviors on Stress-Dependent Unbound Pavement Foundations

Rehabilitation by cracking and seating of concrete pavement optimized by FWD analysis

Performance-based design method for railway asphalt concretereinforced roadbed

Revision of the French reference document of frost design method for High Speed Railway Lines.

Ballastless Tracks on Asphalt Pavements

Mitigation of ground borne noise in rock railway tunnelsPart I: Track design and simulation

Mitigation of ground borne noise in rock railway tunnels - Part II: Full scale tests

Pavement Strengthening and Rehabilitation in Norway - Assessing the needs

Parametric Sensitivity Analysis for the FAA’s Airport Pavement Thickness Design Software LEDFAA-1.3

Austrian Design Standards for Block Pavements

Design of flexible pavement layers

Estimation of the Sensitivity of Design Input Variables for the Mechanistic-Empirical Design Guide

Design of a specific bituminous surfacing for orthotropic steel bridge decks : application to the Millau Viaduct

A non-linear elastic material model and its application in pavement design

Design of Proof Rolling Regimes for Heavy Duty Aircraft Pavements

Selection of Input Parameters for Layered Elastic Design of Flexible Aircraft Pavements

Pavement Response due to Torsional Surface Loading

Structural Design of Pavement for Cold Regions based on Life-Cycle Cost

Rehabilitation of Airport Pavements: The Experience of Linate Airport

Mitigation of ground borne noise in rock railway tunnelsPart I: Track design and simulation