Physical Hardening: From Binders to Mixtures

The significant effect of physical hardening on asphalt binder properties at low temperature is well documented. However, there are very few studies addressing physical hardening in asphalt mixtures. This paper investigates physical hardening effect on asphalt mixtures creep behavior at low temperatures. Bending Beam Rheometer (BBR) creep tests were performed on asphalt binder and asphalt mixture beams conditioned at the test temperature for 1h and 24h to quantify physical hardening effects. Both laboratory-prepared and field samples were used. For all asphalt binders, the additional conditioning time resulted in significant increase in creep stiffness and in significant reduction in m-values. For asphalt mixtures, much less significant changes are observed, and the type of aggregate appears to be significant. A semi-empirical model is used to predict asphalt mixture creep stiffness from binder creep stiffness to better understand the role played by the aggregate matrix in physical hardening.