Laboratory and Construction Evaluation of Warm-Mix Asphalt

Abstract

Warm mix asphalt (WMA) describes various technologies that allow asphalt mixtures to be produced at lower temperatures as compared with hot mix asphalt (HMA). WMA technologies also offer improvements in workability, cost, and environmental sustainability, such as reduced fuel usage, greenhouse gas emissions, and wear and tear at plants, while enhancing worker health and safety conditions. The objective of this study was to quantify the laboratory performance of field-produced mixtures that utilize WMA technologies and to evaluate the influence of lowering the production temperature on the mixture properties in the field. To achieve this objective, three field projects across Louisiana were selected to provide eight mixtures for the evaluation of WMA technologies. Plant-produced mixtures were sampled and the laboratory performance of WMA mixtures and conventional HMA was evaluated. Further, the characteristics of WMA mixtures were compared with conventional HMA mixtures during production and construction. Based on the results of the experimental program, it was concluded that there was no difference in the rutting performance of WMA compared with HMA. In addition, the use of WMA technologies improved asphalt mixture fracture resistance. With respect to moisture susceptibility, the tensile strength ratio (TSR) of the WMA mixtures was comparable to the conventional HMA in two projects; however, it was lower than the TSR criterion of 80% in the third project. During production, while the moisture content in WMA was slightly higher than the conventional mixtures, both mixture types met Louisiana’s specifications (with moisture content less than 0.3%). Further, asphalt absorption was not statistically different between HMA and WMA. During paving, the temperature of the mat was distinctly lower for WMA than for HMA. With respect to the compaction effort, there seemed to be no discernible difference in the compaction effort required for HMA and WMA. In addition, the WMA mixtures were able to meet the minimum specification requirement of 92% density in most of the cases.