Using the Surface Free Energy Method to Evaluate the Effects of Polymeric Aggregate Treatment on Moisture Damage in Hot-Mix Asphalt

Moisture damage in hot-mix asphalt (HMA) occurs because of a loss of adhesion and/or cohesion, resulting in the reduced strength or stiffness of the HMA and the development of various forms of pavement distress. There are several different approaches for improving adhesion and reducing moisture sensitivity in asphalt mixtures. One convenient approach is coating the aggregate surface with a suitable agent to reverse the predominant electrical charges at the surface and reduce the surface energy of the aggregate. In this research, the effects of two types of polyethylene (PE), namely high-density polyethylene (HDPE) and low-density polyethylene (LDPE), were added to coat the aggregate, and the moisture damage to the asphalt mixtures was evaluated. Three types of aggregates representing a considerable range in mineralogy (limestone, granite, and quartzite) were evaluated during the course of this study. This paper explains the theoretical and experimental concept of predicting moisture damage in asphalt concrete mixes using the surface free energy (SFE) concept and laboratory testing analysis, respectively. It also shows the effects of polymeric aggregate treatment on moisture damage within the mixes. SFE measurements were used to compute the work of adhesion between the aggregates, asphalt, and the cohesive bond strength in the asphalt binder and aggregate. The SFE characteristics of three types of aggregate with and without PE treatment and asphalt were evaluated for moisture-damage susceptibility using a universal sorption device (USD) and dynamic Wilhelmy plate method, respectively. To validate these results, a dynamic modulus test was used to apply a repeated unconfined, compressive load to the sample in a controlled stress mode. The results of the SFE method indicate that PE increases the wettability of asphalt binder on the aggregate and the adhesion between the asphalt binder and aggregate. The same results were achieved using the values obtained by laboratory testing analysis. The aggregates treated with HDPE showed better resistance against moisture damage in both methods of study.

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