System for the Evaluation of Moisture Damage Using Fundamental Material Properties (0-4524-1)

Moisture damage in asphalt mixtures can occur within the mastic (cohesive fracture) or at the aggregate-mastic interface (adhesive fracture or failure). Whether or not a cohesive or adhesive failure occurs depends on the nature of the mastic and the relative thickness of the mastic. This report is part of a project that focused on fundamental understanding of the moisture damage process by carefully considering the micro-mechanisms that influence the adhesive interface between aggregate and asphalt and the cohesive strength and durability of the mastic. The first phase of the project focused on the validation of the surface energy measurements and the dynamic mechanical analysis (DMA) of mastics through the evaluation of the moisture susceptibility of materials with known field performance. The results of the first phase of this project were documented in TxDOT report 0-4524-2. The second phase of the project, which is documented in this report, focused on the evaluation of the surface energy and moisture susceptibility of wide combinations of aggregates and asphalts. The analysis approach of moisture damage that was used for the evaluation of mastics in phase 1 was extended in phase 2 to analyze full asphalt mixtures. Also, the influence of binder modifications made by the manufacturer, aging of the asphalt binder, addition of liquid anti-strip agents to the asphalt binder, and changing of the pH of the water at the asphalt-aggregate interface on surface energy parameter developed under NCHRP 9-37 was used as a screening parameter for evaluating the compatibility of asphalt binders and aggregates in terms of the resistance to moisture damage. The ER combines the cohesive and adhesive bond energies in to a single term. A comprehensive system was developed for the evaluation of moisture damage. The first step in the system is to examine the compatibility of an asphalt-aggregate combination by evaluating the surface energy components and the ER. The second step in the system is to conduct DMA of a mastic specimen made of the asphalt binder and fine aggregate portion of the mix. If the DMA results are favorable, the third step, which is the evaluation of the moisture susceptibility of the full mixture, is conducted in order to examine the suitability of mixture design and volumetrics in resisting moisture damage.