Laboratory evaluation of foaming-based and chemical-based warm mix asphalt

A recent joint study by Arizona State University and the Arizona Department of Transportation (ADOT) was conducted to evaluate certain warm mix asphalt (WMA) properties in the laboratory. WMA material was taken from an actual ADOT project that involved two WMA sections. The first section used a foamed-based WMA admixture, and the second section used a chemical-based WMA admixture. The rest of the project included control hot asphalt mixture. The experimental plan included three main objectives. The first objective was to explore the concept of re-heating WMA by conducting the dynamic modulus |E*| at 21.1 °C (70 °F) and compare plant to laboratory prepared mixtures using specimens from the foaming-based mixture. The second objective was to evaluate the effect of WMA on the compaction energy. The third objective was to assess the moisture damage using the Hamburg wheel-track test and AASHTO T-283 tensile strength ratio (TSR) test. The |E*| results tested at 21.1 °C for both laboratory prepared and plant foaming-based mixtures showed similar |E*| values. The statistical analysis indicated that there is no statistical significance of the dynamic moduli between the two mixtures at two compaction temperatures 132 °C (270 °F) and 154 °C (310 °F). This indicated that there is no effect of re-heating on the plant produced WMA mixture. The compaction energy results supported the conclusion from the re-heating study. The moisture sensitivity evaluation based on the TSR results indicated low resistance to moisture damage; while the Hamburg testing results indicated very good performance.