Moisture susceptibility of Warm-Mix Asphalt

Economic, environmental, and engineering benefits led to the rapid implementation of Warm-Mix Asphalt (WMA) during the past decade. While WMA technologies are generally performing well to date, development of standard mix design protocols continues and performance questions remain. This study evaluated laboratory conditioning protocols for WMA to simulate early life when they are more moisture susceptible and proposed 2 hours at 116 degrees C for mix design and reheating to this temperature for quality assurance for all WMA technologies except foaming which requires reheating to 135 degrees C. Next, WMA was shown to be more moisture susceptible as compared to Hot-Mix Asphalt in the early life based on a comprehensive analysis of three standard laboratory tests (wet and dry indirect tensile strengths and resilient modulus and their ratios and Hamburg Wheel Tracking Test stripping parameters) from four field projects that included nine WMA mixtures. Finally, an evaluation of performance evolution showed that WMA can overcome this vulnerability to moisture after a summer of aging and proposed 5 days oven aging at 85 degrees C to capture this effect in the laboratory. Proposed conditioning protocols, aging protocols, and criteria for the tests utilized are provided for WMA mix design and analysis to preclude moisture susceptibility.