Field and laboratory evaluation of fracture resistance of Illinois hot-mix asphalt overlay mixtures

A major study of reflective cracking of asphalt overlays that are used in conjunction with interlayer systems for reflective-crack control was recently completed. In this cooperative study at the Illinois Center for Transportation, three field projects in central Illinois were selected and extensive coring was performed. Six fundamentally different types of hotmix asphalt overlay mixtures, which were expected to demonstrate significantly different levels of fracture resistance, were obtained from coring. To evaluate the fracture resistance of these mixtures in the field and the laboratory, visual field crack surveys and a series of advanced laboratory tests were conducted. This paper presents field performance evaluation results for the performance-benefit ratio and laboratory performance evaluation results for creep stiffness (S_t), complex modulus (E^*), and diskshaped compact tension fracture energy (G_f). Field performance of pavement sections with premium overlay mixtures was found to be superior to those sections containing conventional overlay materials. The polymermodified overlay section in one of three projects was found to have performance inferior to that of the unmodified control overlay section of the same project. This tendency was detected by the G_f test but not by the S_t or the E^* tests. The S _t and G_f values obtained for the interlayer mixtures were consistent with results typically obtained on short-term aged specimens, validating the appropriateness of the coring and testing approach used here as a forensic investigation tool and indicating that little aging had occurred in the bottom of the overlay system.