Laboratory Evaluation and Field Implementation of Polyethylene Wax-Based Warm Mix Asphalt Additive in USA
The use of Warm Mix Asphalt (WMA) for the construction of roads around the world is growing rapidly. This paper presents a new organic WMA product that has been recently introduced to the US market, which is Polyethylene (PE) Wax-based WMA additive with crystal controller to increase the low temperature cracking resistance and anti-stripping agent to enhance moisture susceptibility. To determine the optimum dosage rate, the viscosities of the binder with varying amounts of additive were measured. Based on the Asphalt Binder Cracking Device (ABCD) test, it was found that the low-temperature cracking temperature of asphalt binder would not be affected by the amounts of the additive up to 3.0%. The new Polyethylene (PE) Wax-based WMA mixtures with Reclaimed Asphalt Pavement (RAP) materials were also tested using the Hamburg wheel tracking device and the wheel passes were significantly higher with WMA mixtures PG 64-28 binder, Minnesota aggregates and 25% RAP than the ones with 64-22 binder, Iowa aggregates and 10% RAP. The Hamburg test results seemed to be influenced by more on the characteristics of aggregates and RAP materials than the WMA additive. Two in-service roads in Iowa and Minnesota were successfully rehabilitated using the PE Wax-based WMA mixtures. The average void of 3.8-cm (1.5-inch) WMA overlay (9.0%) was higher than that of HMA overlay (7.0%) placed on an urban street in Iowa City. It was partly due to asphalt temperature that was lowered to match the lower aggregate temperature. However, it is interesting to note that the average air void of the cores obtained from the rehabilitation section of the same street using the same WMA was significantly lower (6.0%). In Minnesota’s state highway, the average air voids of four WMA and HMA cores for quality control were 5.85% and 5.29%, respectively and those of four other WMA and HMA cores for quality assurance were 6.05% and 6.01%, respectively. The WMA pavements were easier to reach 94% density with fewer passes of a compactor than the HMA.