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

Résumé

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.