The literature review demonstrates that a mechanism exists that enhances fatigue life of asphalt concrete mixtures as rest periods are introduced in fatigue testing. Results are presented and analyzedfrom controlled displacement, cyclic crack propagation tests in which rest periods were randomly introduced. The results demonstrate that a "healing" mechanism does indeed result in the requirement of a greater level of work to drive a crack following a rest period than was required before the rest period was introduced. The effort to identify the mechanism of chemical healing in the microcrack process zone is confounded by the concomitant occurrence of viscoelastic relaxation. Schapery's correspondence principle of nonlinear viscoelastic media was successfully used to separate viscoelastic relaxation from chemical healing. Application of the procedure of separating out the viscoelastic relaxation yields a method by which to quantify chemical healing in the microcracks of the process zone preceding the macrocrack. Chemical healing as a function of rest periods is quantified using a healing index based on pseudo-energy-density. This healing index is presented for three asphalts of varied composition. Thispaper appears in transportation research record no. 1228, Asphalt mixtures and asphalt chemistry.
Samenvatting