Long-term field rutting and moisture susceptibility performance of warm-mix asphalt pavement

Although warm-mix asphalt (WMA) has been used in pavement construction in recent years, the long-term field performance of WMA pavements has not been studied extensively. In response, this study investigated 28 pavement projects in the United States, covering different climate zones, WMA technologies, service years, pavement structures, and traffic volume levels. The long-term field rutting performance between WMA pavements and hot-mix asphalt (HMA) pavements was compared. Field samples were extracted for laboratory experiments. Significant determinants (engineering or material properties) that correlate with rutting performance also were investigated. A simple rutting resistance index obtained from the Hamburg wheel-tracking test was found to be the significant determinant (material property) that correlates best with field rutting performance. The significant mix design parameters that affect the rutting resistance index were analyzed to suggest a better rutting-resistant mix design. In addition, no moisture damage or raveling was observed for the selected projects in the field. Therefore, the moisture susceptibility of the mixes was evaluated in regard to the stripping inflection point of field cores as obtained from the Hamburg wheel-tracking test results. It was found also that most of the mixes that did not include an antistripping agent exhibited a stripping inflection point, suggesting the need for the addition of an antistripping agent in pavement mixtures.