Evaluating the Effect of Warm-Mix Asphalt Technologies on Moisture Characteristics of Asphalt Binders and Mixtures

The effect of warm-mix asphalt (WMA) technologies on the moisture susceptibility of a mixture and the adhesion characteristics of the asphalt binder used in it was evaluated. A 9.5-mm Superpave® mixture designed with performance-grade asphalt PG 64-22 was used as the control mixture. Four types of WMA technologies were evaluated: Advera, Evotherm, Sasobit, and SonneWarmix. The Hamburg wheel-tracking device (HWTD) was used to evaluate the effect of each WMA technology on the moisture susceptibility of the mixture at three aging times and three aging temperatures. A liquid antistrip and hydrated lime were added to any mixture that failed the HWTD to determine if they could correct the failure. Because the moisture susceptibility of a mixture is related to failure in the adhesive bond between the binder and the aggregate, a pulloff test, the bitumen bond strength (BBS) test, was used to evaluate the impact of the WMA technologies on the adhesion characteristics of the asphalt binder. The HWTD test results indicated that the moisture resistances of all mixtures improved significantly with an increase in aging time or temperature. Mixtures aged at longer times and at higher aging temperatures exhibited the best performance. The addition of the antistrip agents improved the HWTD results. The BBS test showed that only Sasobit had a significant effect on the pull-off tensile strength of the binder, although only under dry conditions. Overall, no correlation between the BBS and the HWTD was found.