A cracking methodology to assess fracture and fatigue properties of asphalt concrete mixtures using overlay tester

Several highway agencies have either implemented or considered implementing performance tests to predict the cracking potential of asphalt concrete (AC) mixtures in the laboratory setting. One such test, the Overlay Tester (OT) test, measures the number of cycles to failure of the AC specimens by simulating the opening and closing of the cracks induced by daily temperature variations and high tensile strain generated by the traffic load. The variability of the OT test results is expressed as a major concern in reliably characterizing the cracking potential of the AC mixes. The performance of the OT test, in general, and current performance index, in particular, were evaluated in this study. The consistency of the current performance index and potential parameters that can be measured from the OT was comprehensively investigated with two different AC mix types. A cracking methodology and performance indices were implemented considering the crack initiation and propagation phases of the OT test. The consistency and repeatability of the proposed performance indices, critical fracture energy and crack progression rate, seem to be better than the acceptable repeatability level defined as a coefficient of variation (COV) of less than 20%. The proposed cracking methodology and preliminary failure limits seem to characterize and discriminate satisfactorily the cracking resistance of several AC mix types commonly used in Texas. A parametric study using synthetic specimens was conducted on key variables (e.g., glue type and gluing method) considered in the current OT specifications (Tex-247-F) to improve the specimen preparation and testing processes. The improved OT test method was preliminary validated with OT tests on field cores from pavement sections with known field performance. Given its promise in this study, the improved OT test method is recommended as a routine test during the mix-design process of AC mixes