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South Dakota Department of Transportation
Project Synopsis

Title: Asphalt Concrete Anti-Stripping Techniques
Project Researcher: Peter Sebaaly, University of Nevada, Reno
Project Manager: Dan Johnston
Research Period: 7/1/1999 - 10/31/2002
Cost: $80,000.00

Problem Statement: SDDOT has been using lime as an anti-strip additive for asphalt concrete (AC) for a number of years as initial laboratory testing showed it to be a superior anti-strip agent. Recently, contractors have complained about personnel exposure and problems handling lime. They have requested the substitution of liquid or other anti-strip agents, instead of lime, to reduce moisture susceptibility. The problem is complicated by the lack of a suitable test of moisture susceptibility which can reliably predict field performance. For example, Minnekahta limestone does poorly on tests such as ASTM D4867M Effect of Moisture on Asphalt Concrete Paving Mixtures but, as a calcareous aggregate, should not be very susceptible to stripping and has not exhibited a stripping problem in the field.

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.

Research Objectives:
1  To recommend improvements to the lime addition process that minimize personnel exposure and environmental impacts and that assure control of lime addition rate.
2  To determine which available anti-stripping technologies are appropriate for field testing to insure long term performance.
3  To develop guidelines for future use of anti-stripping agents based on field performance, including economic factors, along with necessary testing protocols, specifications and procedures.

Research Tasks:
1  Review and summarize literature relevant to AC moisture susceptibility and mitigation of stripping.
2  Meet with the technical panel to review project scope and work plan, especially with regard to the installation of test sections during the 1999 construction season.
3  Conduct a survey to determine the state of the art for current moisture susceptibility testing and anti-stripping technologies with an emphasis on current practices in surrounding states.
4  Evaluate the performance of two existing field test sections near Brookings, SD incorporating a liquid anti-strip agent.
5  Examine current lime addition practices to determine alternative strategies that minimize safety and environmental concerns.
6  Conduct laboratory testing of candidate anti-stripping technologies including moisture susceptibility, stripping potential under load (Hamburg or other test protocol), resilient modulus, and asphalt concrete properties.
7  Develop and submit plan notes for inclusion into two construction projects, one in each of the 1999 and 2000 construction seasons. The plan notes should define a series of a minimum of four test sections, including a control, per project designed to
8  Monitor and evaluate the construction of the test sections and document test results obtained during construction. Conduct additional testing deemed necessary on materials and samples from test sections including moisture susceptibility, asphalt cont
9  Monitor and evaluate the initial performance (including Falling Weight Deflectometer and other additional testing) of the test sections through the conclusion of the research and note any significant differences.
10  Recommend improved testing and evaluation procedures, practical guidelines and specification changes that will ensure improved handling of lime addition and provide alternative anti-stripping technologies which perform on an equal basis to lime and a
11  Submit an Interim Report after 12 months detailing progress and recommending guidelines or specification changes that can be implemented prior to the conclusion of the research.
12  Prepare a final report and executive summary of the literature review, research methodology, findings, conclusions, and recommendations.
13  Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.

Documents Available:

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