Effects of air void size distribution, pore pressure, and bond energy on moisture damage

The relationship between hot mix asphalt moisture damage, air void structure, pore pressure, and cohesive and adhesive bond energies was investigated in this study using mixes with two different aggregate types (limestone and granite). Each of the mixes was designed with varying gradations to obtain different air void distributions among specimens. Moisture damage was evaluated using parameters derived based on the principles of fracture mechanics. Air void distribution was analyzed using a probabilistic approach with the assistance of X-ray computed tomography and image analysis techniques. The cohesive and adhesive bond energies of the mix were calculated using experimental measurements of aggregate and asphalt surface energies. Permeability, which controls the ability of the water to infiltrate into and drain out of the mix, was expressed as a function of statistical parameters of the air void distribution. Ranges of air void distributions and permeability were identified for each of the limestone and granite mixes at which moisture damage was maximum. The difference in moisture damage between the granite and limestone mixes was explained based on air void distribution and cohesive and adhesive bond energies.