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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 project evaluated the influence of anti-strip additives on the durability and moisture susceptibility of granite-based open-graded friction course, referred to as FC-5 asphalt mixtures. The laboratory testing involved two granite-based FC-5 mixtures containing 1% hydrated lime (by weight of aggregate), 1% hydrated lime plus 0.5% liquid anti-strip (LAS) additive (by weight of asphalt binder), 1.5% hydrated lime, and 1.5% hydrated lime plus 0.5% LAS additive. Two sources of granite aggregates were obtained: one from Junction City, Georgia and the other from a regional supplier with an original source from Nova Scotia, Canada. Four types of LAS additives were collected from Road Science ArrMaz, Inc. and Ingevity, Inc. The binder bond strength test was used to select the LAS agents that provided the best improvement in moisture resistance. The FC-5 mixtures were fabricated in the laboratory using two FC-5 mix designs provided by the Florida Department of Transportation. The specimens were conditioned by the asphalt pavement weathering system to simulate the long-term aging and moisture conditioning in the field. Mixture performance tests, including the Cantabro test, tensile strength ratio test, and Hamburg wheel tracking test, were used to comprehensively evaluate the durability and moisture susceptibility of FC-5 mixtures. Finally, a cost-benefit analysis was performed to determine the cost-effectiveness of the FC-5 mixtures with anti-strip additives. This project found that the addition of LAS additive, extra 0.5% hydrated lime, or both produced longer lasting FC-5 mixtures, and the additional anti-strip additives would improve the cost effectiveness of FC-5 mixtures.
The objective was to conduct a laboratory investigation of moisture susceptibility and rutting resistance of non-foaming warm mix asphalt (WMA) mixtures containing moist aggregates. Gyration number and weight loss of various samples, indirect tensile strength (ITS), tensile strength ratio (TSR), rut depths of dry and moisture conditioned specimens, as well as failed temperatures and rutting factors of recovered binders were measured for all mixtures. The experimental design included two aggregate moisture contents (0 and ~0.5 % by weight of the dry mass of the aggregate), two lime contents (1 and 2 % lime by weight of dry aggregate) and one liquid anti-stripping agent (ASA), three non-foaming WMA additives (Cecabase®, Evotherm®, and Rediset®) with control, and two aggregate sources. A total of 34 mixtures were designed and a total of 340 specimens were tested in this study. The test results indicated that the aggregate source significantly affects the ITS and rutting resistance regardless of the WMA additive, ASA, and moisture content. In addition, the ITS and rut depth of the non-foaming WMA mixtures containing moist aggregates generally satisfied the demand of pavement without additional treatment. The mixtures with three WMA additives exhibited similar rutting resistance under dry and wet conditions. The liquid ASA, used in this study, for moisture resistance is not recommended to use in WMA mixtures containing moist aggregates as the aggregate is sensitive to moisture.
Ohio Department of Transportation has adopted the hot mix asphalt concrete containing polymer modifiers for use in the interstate highway pavement. Among the various reasons cited for the adoption of polymer modifiers are the favorable field experiences by ODOT, extensive literatures reporting enhanced performance, such as rutting resistance, low temperature thermal cracking resistance, and possibly fatigue endurance. However, despite these favorable findings, there are still cases involving premature failure of hot mixtures containing polymer modifiers. Concerns regarding optimum polymer content, compatibility between polymer additives and asphalt cement, proper mixing and compaction procedure remain to be resolved. Furthermore, performance based specifications to ensure production of desirable final asphalt concrete product require additional development. Questions regarding the suitability of Superpave binder testing procedures for the polymer-modified binders need to be clarified.