Development of a test method for evaluation and quantification of healing in asphalt mixture

Abstract

It is now well recognised that microdamage healing may extend the fatigue life of asphalt pavement. In this study, a test was developed to quantify the healing of asphalt mixture, both dense-graded and open-graded, using the Superpave^TM Indirect Tensile Test testing system. The healing test consists of repeated load damage tests (resilient modulus tests) during the damage phase followed by a healing phase during which resilient modulus tests are performed on a limited basis to measure modulus recovery (healing). Appropriate load level, as percentage of tensile strength, for the damage phase was found to depend on mixture brittleness index. A decrease in resilient modulus with an increasing number of load cycles is indicative of accumulation of microdamage during the damage phase. Recovery of resilient modulus during the healing phase is indicative of damage recovery or healing. Rate of healing was found to not be constant but rather changed with time at a decreasing rate for any given mixture. Therefore, a healing rate parameter was defined to allow for comparison between mixtures. Results showed that, in general, expected trends were observed. Mixtures tested at higher temperatures healed at a faster rate than those at lower temperatures and mixtures subjected to less oxidative ageing healed at faster rates than those subjected to more oxidative ageing.

Keywords:

• healing
• asphalt mixture
• repeated loading
• brittleness index

Acknowledgements

The authors would like to express their gratitude to the Florida Department of Transportation for providing the financial and technical support that made this research possible.