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

Resumé

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.