The overall effect of using lime as an anti-stripping agent provides additional benefits beyond lowering stripping potential as it increases the stiffness of the mix, reduces asphalt requirements and is less sensitive to asphalt cement properties. Lime has an extensive track record nationally and is acknowledged as a superior anti-stripping agent. Many of the liquid or polymer anti-stripping agents are relatively new technologies, may be asphalt sensitive and may adversely affect AC concrete properties in terms of overall performance. In addition, it is difficult to verify the actual amount of anti-stripping agent in the asphalt cement. Some liquid anti-stripping agents, when employed at too high a dosage, can actually increase stripping susceptibility. The level of confidence in allowing the use of alternative anti-stripping agents is not currently sufficient enough to justify substitution, even though there may be a significant cost savings in doing so. This research is proposed as a means of providing the guidance based on field performance necessary to make an informed decision with regard to future use of anti-stripping additives. In addition, the research will investigate ways to minimize safety and environmental concerns when lime is used as an anti-stripping agent.
Findings: In 1999 the South Dakota Department of Transportation initiated a research project to assess asphalt concrete anti-stripping techniques. The overall objective of the research was to evaluate the effectiveness of anti-stripping additives in reducing the moisture damage of HMA mixtures. The research evaluated the best method of adding lime to HMA mixtures to minimize personnel exposure and environmental impacts, determined the effectiveness of other anti-stripping additives, and developed guidelines for future use of anti-stripping additives in South Dakota.
The research constructed six test sections at two locations in the eastern and western parts of the state, respectively. The test sections included none (control), lime, UP5000, and liquid anti-strip additives. The mixtures were sampled during construction and two years after construction. The moisture sensitivity of the various mixtures was evaluated in the laboratory using resilient modulus, tensile strength, resistance to permanent deformation, and resistance to thermal cracking. The analysis of the laboratory data indicated that the addition of lime has the best potential of reducing the moisture sensitivity of South Dakota's asphalt concrete mixtures. On the other hand, the two years in-service did not show any significant variations in the performance of the various treatments. Based on the data generated from this research, it has been recommended that lime on wet aggregate should be used to minimize moisture damage of asphalt concrete mixtures in South Dakota.