Everett Crews

Field Performance of Warm-Mix Asphalt at National Center for Asphalt Technology Test Track

Warm-mix asphalt (WMA) mixes produced by an emulsion process were evaluated under accelerated loading in three total sections of the National Center for Asphalt Technology Test Track and used as the surface mix for two of the sections. Evotherm was incorporated into the same mixes used previously on the track. In-place densities of the WMA surface layers were equal to or better than the hot-mix asphalt (HMA) surface layers, even when compaction temperatures were reduced by 8°C to 42°C (15°F to 75°F). Laboratory rutting-susceptibility tests conducted in the asphalt pavement analyzer indicated similar performance for the WMA and HMA surface mixes with the PG 67-22 base asphalt. However, laboratory tests indicated an increased potential for moisture damage with the WMA mixes. The two WMA sections and the HMA section showed excellent rutting performance in the field after the application of 515,333 equivalent single-axle loads in a 43-day period. One of the WMA sections was also evaluated for quick turnover to traffic and showed good performance.

Prediction of Stiffness of Asphalt Treated with Surfactant-Based Warm-Mix Additive

Although the tonnage of asphalt pavements constructed with warm-mix technologies has increased rapidly in the United States in recent years, some practical aspects of warm-mix asphalt pavement construction remain incompletely defined. For example, compaction temperatures for many warm-mix technologies cannot be estimated with the standard equiviscous methods common to hot-mix asphalt. This paper reports the preliminary results of research to develop a method for predicting the stiffness (G*/sin δ) of binder treated with a surfactant-based warm-mix additive as a function of mix production temperature, mix storage and haul time, and warm-mix additive dosage. Asphalt binders were treated in the laboratory with 0.0%, 0.5%, and 1.0% of surfactant-based warm-mix additive and were heated in a rolling thin-film oven at 130°C, 145°C, and 163°C for 0, 25, 55, 85, and 115 min. Regression analyses of the laboratory data yielded equations that with good fit correlated binder stiffness with the formulation (dosage) and process variables (aging temperature and time). The predictive value of these laboratory-developed equations was found to be good when the measured stiffness of binder extracted from field mix obtained at the paver was compared with binder stiffness calculated with the laboratory-developed equations by using the plant mix temperature, total storage and haul time, and surfactant dosage.