Case Study of Warm-Mix Asphalt Moisture Susceptibility in Birmingham, Alabama

Abstract

One of the main concentrations of warm mix asphalt (WMA) research is now on the durability and performance of WMA pavements overtime. Specifically, one of the major concerns with WMA is the ability to resist moisture damage. The concern about moisture resistance stems from lower moisture susceptibility results in the laboratory in comparison to hot mix asphalt (HMA) (1-7). It has been hypothesized that the lower temperatures may not allow for proper drying of aggregates. If moisture remains in the aggregates, it could prevent binder and aggregate from adequately bonding. There is also some concern related to the lack of absorption of asphalt for WMA in comparison to HMA. If asphalt is not filling the voids in the aggregate than there is a potential for moisture to fill those voids. However, despite lower moisture susceptibility results for WMA in comparison to HMA, field evaluations thus far of WMA pavements have not noted any issues with moisture damage. In this paper, moisture susceptibility test results for both laboratory and plant produced mixes are compared. The mixes evaluated were used as part of the August 2007 WMA demonstration in Alabama. Three moisture susceptibility measures were used to assess the moisture susceptibility of the two mixes. The results indicated that the laboratory produced WMA was more prone to moisture susceptibility than the plant produced mix. The HMA exhibited more favorable moisture susceptibility values than the WMA, however, most of the WMA samples did meet the moisture susceptibility criteria.