Accumulated strain in polymer-modified asphalts

One of the distress modes of asphalt pavements is the rutting that occurs at high operating temperatures, and it is believed that the accumulated strain in asphalt binder is mainly responsible for the rutting. The asphalt industry has tried to use the parameter 1/J″ as the specification parameter for the determination of the susceptibility of asphalt pavements to rutting. It was, however, recognized that this parameter is not suitable for polymer-modified asphalts, and currently, the repeated creep and recovery test (dynamic creep test) is studied as a new specification tool. In this paper, we study the general response of binders to a train of shear-stress pulses with a constant rest time between the pulses. We have found that the viscous approximation of the creep compliance function yields a suitable description of the test when the creep recovery is very weak. To extend the description to cases with significant recovery, an alternative model is proposed. Using the simple approximation of the continuous retardation spectrum, L, by the reduced loss compliance, L is modeled by a gamma-type distribution function. With this form of the shear compliance function, one can successfully describe the dynamic creep test in various polymer-modified asphalts.