Innovative methods for quantifying the moisture susceptibility of asphalt mixtures

Moisture damage in asphalt mixtures can cause early cracking and rutting failures due to the internal damage accumulated by the high internal pore pressures created at the aggregate-binder interface and/or within the binder phase by heavy traffic loads. Tensile strength ratio (TSR) test results have not been effective indicators of moisture susceptibility of the asphalt mixtures. Therefore, a reliable moisture conditioning method and moisture susceptibility test need to be developed and implemented to determine the possible long-term impact of several new additive technologies on pavement longevity. In this study, different tests and conditioning methods for moisture susceptibility quantification of asphalt mixtures were evaluated, and a new test method incorporating a color measuring device was also developed that could identify the impact of different anti-stripping agents and warm-mix additives on moisture susceptibility of asphalt mixtures. Results indicated that the moisture-induced stress tester (MIST) conditioned and vacuum conditioned samples showed similar susceptibility towards rutting and moisture. Moreover, the CT-index parameter was not found to correlate with the moisture susceptibility of the mixes. Based on the results of the laboratory investigations, this study recommends the use of a colorimeter in conjunction with the current TSR method to determine the adhesion and cohesion-related moisture susceptibility.