Laboratory moisture susceptibility evaluation of WMA under possible field conditions

Abstract

One of the major concerns with WMA is degradation due to the presence of moisture during production. In the field, moisture in the aggregates may not be completely expelled due to a lower production temperature which increases the potential for moisture damage, including stripping. The objectives of this paper are: (1) to investigate the impact of hydrated lime on the moisture resistance of WMA mixtures prepared using saturated surface dried (SSD) moist aggregates; (2) to examine the effects of multiple freeze–thaw cycles on the moisture susceptibility of WMA mixtures. Testing samples were prepared in the laboratory with the materials from a local asphalt plant in Michigan according to the Superpave mix design. The control samples (HMA) were mixed and compacted at 165°C and 155°C, respectively. The WMA samples were prepared using different additives, which were Advera, Sasobit, Cecabase RT, and water as a foaming agent. For the moisture susceptibility evaluation, the mixtures were prepared using SSD aggregates and the WMA mixtures were both mixed and compacted at a similar temperature, 130°C. Hydrated lime was added as an anti-stripping agent to determine whether or not it can improve the moisture susceptibility of the HMA and WMA prepared using SSD moist aggregate. The samples for the multiple freeze–thaw study were prepared according to a similar mix design at numerous temperatures (100°C, 115°C and 130°C) and different percentages of WMA additives based on the specific ranges recommended by the manufacturer of each WMA technology. Each additive was added to the asphalt binder prior to mixing with aggregate based on the designated percentage. Based on the results, the presence of hydrated lime in the WMA has resulted in the TSR values passing the minimum requirement of 0.80. This indicates that by adding hydrated lime, the moisture susceptibility of the WMA can be improved. The WMA samples that were tested under multiple freeze–thaw cycles do not perform as well as the HMA samples. Different additives perform better at different quantities in the mixture, as well as at different temperatures. Lower mixing and compaction temperatures negatively affect the TSR after repeated freeze–thaw conditions.