Hot mix asphalt (HMA) moisture susceptibility analysis: material loss to mechanical properties

Numerous studies have been conducted to identify moisture sensitive mixes during mix design by simulating various mechanisms of moisture damage. These methods involve the determination of changes in strength or stiffness of asphalt mixes due to moisture conditioning. The objective of this study is to understand the coupled problem of moisture induced material loss and change in strength/stiffness of the mix. Moisture Induced Stress Tester was used for conditioning samples of a poor and a good performing mixes. This test applies cyclic pressures in the asphalt mix samples through repeated pulses of water. The effluent containing aggregates and binder that were dislodged from the samples during the moisture conditioning process were collected for testing. Both coated and uncoated/fractured aggregates were found in the effluent. The results indicated that the samples with a higher loss of asphalt binder compared to other samples in the investigation during conditioning may exhibit higher tensile strengths, and those with a loss of finer materials, which is indicative of aggregate breakdown, show a lower tensile strength. Both seismic modulus and indirect tensile strength tests were found to be able to differentiate the poor and good performing mixes. For the mixes used in this study, the rate of change in indirect tensile strength during moisture conditioning was found to be strongly correlated to the pre-conditioning modulus of the mix, and a method is suggested for using the threshold values of properties of pre-conditioning mixes for different durations of moisture conditioning during mix design to screen poor mixes in a fast and nondestructive manner.