Antistripping additives are used routinely to improve water resistance of asphalt mixtures. Different additives have different improvement effectiveness in water resistance. In this study, the effects of various additives on the moisture susceptibility of asphalt mixture are studied with the retained Marshall stability test, Lottman test, and immersion wheel tracking test. Asphalt mixtures were modified with Portland cement, hydrated lime, lime slurry, and liquid antistripping agents. The results show that the lime-slurry-treated asphalt mixtures have better resistance to moisture susceptibility than mixtures treated with other materials, and have better long-term moisture stability than the liquid antistripping agents. The liquid-antistripping-agent-treated asphalt mixtures have better resistance to moisture stability before long-term aging. Portland-cement-treated asphalt mixtures show slightly improved water resistance. Asphalt mixtures become more resistant to moisture damage through short-term aging. It was confirmed that the Lottman and the immersion tracking methods are better methods to evaluate moisture susceptibility than the retained Marshall stability methods.

Durability characteristics of certain foamed asphalt mixtures were established during this laboratory investigation. Durability was characterized by a water sensitivity test and cyclic freezing and thawing. The various foamed asphalt mixtures were evaluated for durability after the mixtures had been compacted into 10.16-cm (4.00-in.) diameter by approximately 6.35-cm (2.50-in.) high specimens, and cured.

The use of hydrated lime or other liquid anti stripping agents (ASA) is the most common method to improve the moisture susceptibility of asphalt mixes. However, most laboratory test conditions used to evaluate the moisture susceptibility of the mixes are only for a short duration of time. This might not be a good representation of the field conditions (i.e., several months or years of service). Thus, a study to evaluate the effects of conditioning the mixes for longer durations was initiated. Also, another problem with the use of the liquid anti stripping agents is their heat storage stability. This report addresses these two issues, by preparing and testing mixtures made with fresh binder for indirect tensile strength after conditioning the samples for 1, 7, 28, 90 and 180 days, and samples prepared from binder stored for three days at 160° C after conditioning them for 1, 28 and 90 days. The results of this study indicated that hydrated lime and the liquid anti stripping agents were equally effective for the mixes used in this research when conditioned beyond one day. In the case of samples prepared from stored binder, there was no significant difference in the effectiveness of hydrated lime and the liquid anti stripping agents even after conditioning for one day. Though it was observed that none of the ASA treatments performed better than others in the case of samples prepared with stored binder, it was also observed that almost all mixes gave significantly similar wet ITS and TSR values as samples prepared from fresh binder.

This study used a mechanistic framework (i.e., surface free energy) to evaluate the moisture susceptibility of warm mix asphalt (WMA) with three different WMA additives, namely, Sasobit, Advera, and Evotherm. The surface free energy (SFE) components of modified PG64-22 asphalt binder with different percentages of WMA additives and selected aggregates were measured in the laboratory. The wettability, the work of adhesion, the work of debonding, and energy ratios were estimated in order to assess the moisture-induced damage potential of combinations of modified asphalt binders and different aggregates. The results indicate that Sasobit and Advera are able to reduce the moisture susceptibility potential of the mixes, but their use is not recommended with highly acidic aggregates such as granite. Evotherm resulted in the highest increases in wettability, total surface free energy, and increased work of adhesion and a reduction in the work of debonding, resulting in a better possible aggregate coating with asphalt binder and lower moisture susceptibility with all types of tested aggregates relative to those of other WMA additives. Furthermore, tensile strength ratio (TSR) tests were conducted on Advera and Evotherm-modified and neat (unmodified) asphalt mixes, and the results were compared with those from the SFE test. It was found that the SFE approach is a better indicator of moisture susceptibility than the traditional TSR test. The findings of the present study would help the highway engineers and agencies to better understand the moisture damage potential of flexible pavements constructed with WMA technologies.

Moisture damage in asphalt mixtures can cause early cracking and rutting failures due to the internal damage accumulated by the high internal pore pressures created at the aggregate-binder interface and/or within the binder phase by heavy traffic loads. Due to the high precipitation levels and frequent rain events, distresses originating from moisture damage are commonly observed on roadways in Oregon. ODOT has been mostly using hydrated lime to combat distresses related to moisture damage at the mixture level, while the effectiveness of new chemical anti-strips and warm-mix technologies has also started to be investigated. However, a reliable moisture conditioning method and moisture susceptibility test need to be developed and implemented for Oregon to determine the possible long-term impact of several new additive technologies on pavement longevity. Roadway geometry, asphalt layer density, construction of proper superelevation on the roadway for effective water removal, and functioning drainage facilities can be considered to be the other important factors that control moisture-related failures on roadways. Based on the comprehensive literature review and the results of the laboratory investigations, this study recommends the use of a colorimeter in conjunction with the current AASHTO T 283 (2014) method to determine the adhesion and cohesion-related moisture susceptibility. According to the laboratory test results, vacuum saturation is able to create significant moisture damage in the asphalt microstructure, and no other conditioning method needs to be adapted to replace the vacuum saturation method. Developed tools and test procedures are expected to help ODOT identify the benefits of recent additive technologies that are being developed to combat moisture damage of asphalt mixtures.