Fundamental evaluation of moisture damage in warm-mix asphalts

Warm-mix asphalt (WMA) technologies have been used extensively in the last decade. The benefits of WMA have motivated contractors and agencies to expedite the implementation of this technology. However, some research studies have raised concerns regarding WMA laboratory performance in terms of resistance to moisture damage, while WMA has demonstrated good performance in the field. These experiences motivated further research to understand the fundamental characteristics of WMA. This study comprised a comprehensive evaluation of WMA prepared using different aggregate sources, asphalt binders, and WMA additives. A dynamic mechanical analyzer was used to test the mastic phase of conventional hot-mix asphalt and WMA. The test specimens were evaluated at different conditions - dry and wet - and at different aging stages - unaged and 3-month aged - in a controlled environmental room (i.e. 60°C). A fracture mechanics approach was used to analyze the test results. This approach incorporated fundamental material properties including adhesive bond energy between aggregates and asphalt binder. The results show that WMA performance improved with aging and the overall performance of the WMA can be improved if the selection of materials (i.e., aggregate source, asphalt binder, WMA technology) is optimized based on the compatibility of their surface energy. In addition, surface energy results were able to explain some findings from the mechanical testing related to moisture susceptibility of WMA.