Investigation of Aging in Hydrated Lime and Portland Cement Modified Asphalt Concrete at Multiple Length Scales

The properties of asphalt concrete are the result of many interdependent physical and chemical mechanisms occurring across multiple length scales. Admixtures such as hydrated lime (HL) and portland cement (PC) are known to affect the behaviors of asphalt concrete at the macroscale, but their contribution at other scales and influences on overall performance of the material are not well understood. This paper presents the findings of a study that evaluates the potential for HL and PC for mitigating the effects of asphalt concrete aging with respect to modulus and fatigue resistance. The properties of interest were evaluated at multiple scales, which involved binder, mastic, and mixture testing. Rheological analyses of aged and non-aged control, HL modified, and PC modified mastics indicate that HL possesses greater potential to mitigate aging than PC. In mixture testing, the modulus results showed trends similar to that of mastics, in which the HL-modified samples were the stiffest and showed greater potential to mitigate aging. As expected, the relative increase in stiffness and relative potential to mitigate aging, averaged across temperatures, was found to be higher in mastics than the mixtures. The results from the uniaxial fatigue test show that HL mixtures possess higher fatigue resistance when aged, thus less negative effects from the oxidation process. Magnification of aging mitigation potential at the mastic scale, and its direct correlation to fatigue behavior, explains why multiple scale evaluations can be useful in evaluating the true benefits of the admixtures.