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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 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.
TRB's National Cooperative Highway Research Program (NCHRP) Report 714: Special Mixture Design Considerations and Methods for Warm-Mix Asphalt: A Supplement to NCHRP Report 673: A Manual for Design of Hot-Mix Asphalt with Commentary presents special mixture design considerations and methods used with warm-mix asphalt. NCHRP Report 714 is a supplement to NCHRP Report 673: A Manual for Design of Hot-Mix Asphalt. All references to chapters in NCHRP Report 714 refer to the corresponding chapters in NCHRP Report 673.
This Report to Stakeholders reviews some of our transportation research efforts in Wisconsin during the past four years. A few of these studies are already complete and have made a significant impact on the way we do business. Many of the projects will be finished in the coming months. For all of us interested in Wisconsin's transportation future, the report provides an overview of these diverse and laudable investigations.
The purpose of this literature review is to search the literature in the area of chemical and mineral agents used to promote adhesion of asphalt-aggregate mixes. In addition, tests performed to measure the effectiveness of these agents were reviewed. The information gained through this literature search and review provides background information for the research being performed in the SHRP A-003B contract. This literature search was performed using on-line chemical abstracts for documents in the time period of 1967 to present.
Stripping has long been recognized as a cause of asphalt pavement damage. Water may get between the asphalt film and the aggregate surface, causing an adhesive failure, or water may combine with the asphalt to affect the cohesive strength of the material. Various types of antistripping additives have been used in the attempt to alleviate or eliminate stripping. The Virginia Department of Transportation has used antistripping additives in some of its asphalt mixes since the 1960's. In the 1980's hydrated lime was found to outperform several al chemical additives. VDOT began to require asphalt contractors to use chemical additives that produced test results equal or superior to hydrated lime. Presumably, chemical additives were then improved to compete with hydrated lime. This study was undertaken to find if the new generation of additives prevented stripping in Virginia's hot mix asphalt. Twelve test sections were established, 9 using chemical additives and 3 containing hydrated lime. After 3 to 4 years, eight of the sections containing chemical additive demonstrated considerable visual stripping in cores. The sections containing hydrated lime showed much less stripping. The TSR test used on mix sampled during construction did not accurately predict the stripping that occurred. A follow-up survey of existing pavements should be conducted to verify the possible inadequacy of some chemical additives. Also, the TSR test should be examined and possibly modified to more closely duplicate Virginia's environmental conditions.