Effectiveness of Antistrip Agents in Asphalt Mixtures

Since the late 1970s there has been much research performed to understand better the stripping phenomenon in asphalt mixtures. As a result, there have been changes in both materials and technology over the past 30 years to improve the resistance to moisture damage and the ability to test for performance under adverse moisture conditions. Because of the changes in materials and technologies related to the development and improvement of antistrip agents, this research study was conducted to evaluate the effectiveness of current antistrip agents used in hot-mix asphalt pavements. The objectives of this project were to construct a field test section that used three different antistrip agents in a conventional Superpave^® surface mixture and conduct a series of laboratory performance test comparisons using different aging periods to make long-term comparisons of the effectiveness of hydrated lime, liquid additive, and warm-mix asphalt antistrip additives. Multiple freeze–thaw cycles of zero, one, five, and 10 cycles were used for a portion of the research study. The results showed that hydrated lime had the highest tensile strength and highest tensile strength ratio (TSR) values and was the only additive treatment to meet the minimum of 80% TSR for all freeze–thaw cycle combinations. Both five and 10 freeze–thaw cycles were significantly more discriminating for moisture susceptibility than one freeze–thaw cycle alone. Warm-mix asphalt treated mixtures produced low initial tensile strengths, but the strength of these mixtures improved with time.