Moisture damage in hot-mix asphalt (HMA) mixtures occurs when water can infiltrate the pavement system. Pore water in mixtures can cause premature failure of hot-mix asphalt pavements, primarily through loss of adhesion between the asphalt binder and the aggregates or the loss of cohesion in the asphalt binder. Loss of adhesion can lead to stripping and raveling. Loss of cohesion can lead to a weakened pavement that is susceptible to pore pressure damage and premature cracking. Depending on materials, loading, and environment, it may be that one or all of the mechanisms of water damage are present and dominant in a pavement. However, for a proper evaluation of any given mixture and testing procedure, it is necessary to isolate and quantify the effects of each of the predominant mechanisms contributing to moisture damage. For the study described in this paper, two sets of mixtures were prepared. The first group involved fine-grained (above restricted the zone) and coarse-grained (below the restricted zone) limestone mixtures commonly used by the FDOT that were produced with multiple void structure and permeability configurations by varying the gradations and proportions for a common set of aggregates and asphalt cement. The second set of mixtures consisted of three granite-based mixtures commonly used by the FDOT. Nondestructive testing was used to identify and isolate the effects of pore water in mixtures after conditioning. Based on the results from the nondestructive testing, SuperPave(TM) IDT creep, resilient modulus, and strength tests were performed on conditioned and unconditioned mixtures without the complicating effects of the presence of pore water. The results illustrate the effects of moisture damage on the fracture properties of mixtures and the influence of aggregate type and gradation characteristics on moisture damage susceptibility. Water damage in mixtures is complicated by aggregate structure and aggregate type, so that each mixture property is affected differently and to different degrees by water damage from one mixture to another. Based on the results in this study, the use of a single parameter to evaluate moisture damage must be questioned. Rather, a single unified framework that accounts for changes in key mixture properties is needed to consistently evaluate the effects of water damage in mixtures. In this paper, the HMA fracture mechanics framework, developed at the University of Florida, is used to integrate the varying effects of water damage on key mixture properties into a single number (ratio of the number of cycles to failure after and before conditioning) that reflects the change in the cracking performance of the mixture due to water conditioning. The results show that HMA fracture mechanics provides a rational framework for the evaluation of moisture damage in mixtures that accounts for changes in multiple parameters, not just a single parameter. The approach presented can be used to evaluate the effects of water damage, independent of the conditioning procedure. Using a consistent framework for evaluating the detrimental effects of water damage, the effects of various different conditioning procedures can also be evaluated more thoroughly.
