Direct tensile test to assess healing in asphalt

Asphalt concrete has the advantageous ability to heal. During rest periods, damage present in the material is restored to a certain extent. Healing of the material can be observed in its regaining of strength and stiffness after rest periods. In this paper, a new test method is presented. It was developed to increase the understanding of the healing phenomenon. The test method focused on asphalt as it was assumed to be the driver of the healing performance. The test method assessed the healing performance of asphalt in stiffness and strength by testing the bond strength in tensile mode of two pieces of asphalt that were assembled under controlled temperature and stress conditions. With the test method, healing tests were performed on one type of binder; the load level during healing and the healing time were varied. The test results showed that after a short healing time of only 6 min, a significant amount of healing could be detected. That finding indicates the importance of adhesion between two crack surfaces when the healing capacity is assessed. It was also found that the maximum tensile stress reached a plateau value after 24 h of healing; the finding indicates that full healing can be realized in short time periods for pure, unaged, soft binders. It was also shown that the load level perpendicular to the damage during healing had a significant effect on the observed healing.