Laboratory investigation of moisture susceptibility of long-term saturated warm mix asphalt mixtures

Moisture damage in flexible pavements might cause stripping in asphalt pavements and ultimately result in premature failure. Warm mix asphalt (WMA) technology as a means to decrease the energy consumption and emissions associated with conventional hot mix asphalt production is broadly being used recently. However, the utilisation of the hydrated lime and liquid anti-strip additives in WMA mixtures makes these issues more complicated. The objective of this study was to investigate and evaluate the moisture susceptibility of mixtures containing anti-stripping agents (ASAs) and WMA additives after long-term saturated durations. The experimental design for this study included the utilisations of one binder source (PG 64-22), three ASA additives and control, two WMA additives and hot mix, and three aggregate sources. A total of 36 types of mixtures and 540 specimens were fabricated and tested in this study. The performed properties included indirect tensile strength (ITS), tensile strength ratio, flow and toughness. The results indicated that the aggregate source has an effect on dry ITS and flow values but had no effect on wet ITS, wet flow and toughness values. In addition, hot mixture generally had higher dry and wet ITS values, and there were significant differences in flow and toughness values between hot and warm mixtures. Moreover, the hydrated lime exhibited the best moisture resistance in WMA mixtures; the liquid ASA additives could increase the ITS values of mixtures but exhibited a weak moisture resistance in this study. Furthermore, the storage and saturated duration generally had no effect on ITS values, and statistical analysis results did not show any differences among these mixtures.