Development of an Accelerated Long-Term Aging Protocol for Simulating Asphalt Concrete Mixture Aging in Regions with Extreme Climatic Conditions

Abstract

An accelerated laboratory mixture long-term aging (LTA) protocol is developed for applications in extreme climatic conditions. The Phoenix metropolitan area in Arizona, U.S.A., is selected as the region of interest because of its extended exposure to high summer temperatures. The National Cooperative Highway Research Program (NCHRP) 09-54 project recommended a climatic aging index model that predicts the oven aging period to simulate various degrees of field aging at different pavement depths. The laboratory conditioning is determined to be 17 days of loose mixture aging at 95°C. Five different binder types are selected for the development and verification of the accelerated LTA protocol. An accelerated oven aging temperature of 135°C is selected. The equivalent aging period is estimated using the NCHRP 09-54 project kinetic model. Considering practicality, a 30-h oven aging period is selected for the proposed LTA protocol. The applicability of this protocol is investigated using rheological, chemical, and mixture-level fracture experiments. A multitude of parameters are used to compare the proposed LTA protocol with the NCHRP-recommended protocol. The results demonstrate that both LTA conditions are consistent across all tests performed. For modified binders, the two aging conditions produced nearly identical results. However, some discrepancies are observed, particularly in the rheological parameters of the unmodified binders, verifying the additional aging hours predicted by the kinetics oxidation model. The consistency of the results between the two aging temperatures at the mixture level verifies the feasibility of using 135°C as part of a LTA protocol in the balanced mix design applications.