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

Abstract

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.