Influence of production temperature and aggregate moisture content on the initial performance of warm-mix asphalt

The concept and use of warm-mix asphalt (WMA) is becoming more popular in the asphalt industry. The promise of reduced energy consumption, reduced emissions, and a more workable product is appealing to an industry pressured by environmentalists with sustainability agendas and state agencies that apply pay adjustments on the bases of ride quality and pavement density. The use of WMA may come with some potential issues, however. Lower production temperatures may result in softer asphalt because of reduced oxidative aging, while poorly dried aggregates may create a problem from moisture damage. To evaluate these issues, a research project was undertaken to quantify the influence of mixing (production) temperature on the rutting and fatigue cracking performance of WMA mixtures. Stripping potential was also evaluated by using prewetted aggregate blends and by modifying the mixing procedure in the laboratory to more appropriately simulate a drum plant production of WMA. The laboratory procedure clearly indicated a decrease in rutting resistance and stiffness when evaluated in an asphalt mixture performance tester and dry Hamburg wheel tracking (HWT) tests once mixing temperatures decreased. Fatigue cracking resistance meanwhile increased in an overlay tester. Tensile strength ratio (TSR) and wet HWT tests indicated that TSR and Hamburg rutting values were able to obtain only passing results at conventional hot-mix asphalt mixing temperatures and with dry aggregates. The information presented may help state agencies to develop quality control testing plans for future implementation of WMA.