Long-term field performance of flexible pavements using warm mix asphalt technologies

An increased awareness of sustainability in the pavement industry has encouraged the use of warm mix asphalt (WMA) technologies. Compared to conventional hot mix asphalt (HMA) that requires a high production temperature, WMA has several benefits, such as saving fuel and energy, reducing greenhouse gas emissions, and improving the work environment. However, systematic analysis of long-term field performance for pavements containing WMA mixtures has been scarce. Therefore, the objectives of this paper are to evaluate the field performance of flexible pavements using WMA technologies (referred as WMA pavements in this paper) and compare the general trend of the longer-term performance between WMA and HMA pavements across the United States. Specifically, 28 WMA pavement projects along with their companion HMA pavements were evaluated for an extended performance period in terms of transverse cracking, longitudinal cracking, rutting and moisture damage. A companion HMA pavement refers to the an pavement that shares similar pavement structure, climate, traffic conditions and mixture design with the WMA pavement; the main differences are the usage of WMA technologies in the surface layer and the reduced production temperature for WMA mixtures. The selected projects include five projects constructed during the course of the study, and 23 in-service projects covering different service ages, traffic volumes, pavement structures, WMA technologies, and four climatic zones across the United States. It was found that pavements containing various WMA technologies exhibited comparable long-term field performance as compared to that of the companion HMA pavement in terms of transverse cracking, wheel path longitudinal cracking, and rutting. No moisture-related distress was found in the field for either HMA or WMA pavements. Overall, cracking and rutting performance show a clear pattern of climate influence. Cracking distress appears to be more of a concern within wet climatic zones while less typical in dry climatic zones, which suggests that moisture should be considered in evaluating the cracking potential of asphalt mixtures. Results presented herein were part of NCHRP Project 9-49A on the Performance of WMA Technologies: Stage II-Long-Term Field Performance.