Evaluation of low-temperature cracking performance of warm-mix asphalt mixtures

In the field of asphalt concrete, the use of warm-mix asphalt (WMA) has become one of the most popular methods of meeting sustainability demands. Researchers have determined that WMA use can lead to reductions in fuel consumption and emissions. Early literature hypothesized that an additional benefit, regardless of the WMA additive or process used, was decreased susceptibility to thermal cracking. The current study examined this hypothesis through laboratory testing of four WMA mixtures produced at a reduced production temperature and a reference hot-mix asphalt (HMA) mixture. The disk-shaped compact tension, indirect tension, and acoustic emission tests were used to characterize the low-temperature properties of the mixture. The fracture energy results of the disk-shaped compact tension test showed that the chemical additives improved fracture energy in comparison with HMA and that the organic and foaming additives reduced fracture energy. The indirect tension creep compliance test produced similar results, in which the two chemical additive-modified WMA systems increased mixture creep compliance, while the other two systems did not significantly alter creep compliance as compared with the control HMA mixture. Acoustic emission testing provided further information regarding the low-temperature behavior of WMA mixtures. The foaming additive displayed an embrittlement temperature similar to that of HMA, whereas the organic additive increased the embrittlement temperature. The two chemical additive-modified mixtures produced differing embrittlement temperatures. It was concluded that resistance to thermal cracking was not ensured by producing WMA mixtures at lower temperatures. Therefore, performance testing is critical to evaluating WMA technologies in locations susceptible to low temperatures.