IMPLEMENTATION OF SHRP INDIRECT TENSION TESTER TO MITIGATE CRACKING IN ASPHALT PAVEMENTS AND OVERLAYS

This research project focused on the following goals: (1) Use the Superpave Indirect Tension Tester (IDT) to achieve a better understanding of how cracks initiate and propagate in asphalt mixtures - this required the development of testing and data reduction procedures and software to determine fracture resistance from Superpave IDT tests; (2) Based on this understanding, identify the key mixture properties that are necessary to control cracking performance of mixtures and pavements; (3) Develop a framework and/or model for using these properties to evaluate the cracking performance of mixtures and a framework for an asphalt mixture specification based on these same properties; and (4) Provide recommendations for the development of asphalt mixture specification criteria. It was determined that only five mixture properties, which are easily obtained from the Superpave IDT, are needed to control the cracking performance of asphalt mixtures subjected to any loading condition: (1) the m-value, which was determined to be directly related to the rate of microcrack development in asphalt mixtures; (2) the dissipated creep strain energy to fracture (DCSEf), which was determined to be the threshold energy above which macrocracks develop under repeated loading conditions; (3) the total energy to fracture, which was determined to be the threshold energy above which macrocracks will develop under a single critical load; (4) the resilient modulus, which affects the stress level for a given load and pavement structure and is needed to determine DCSEf; and (5) the creep compliance, which affects the thermal stress level for a given cooling condition. Testing and data reduction procedures and software were developed to determine these properties simply and reliably using the Superpave IDT. It was also determined that the rate of micro-damage healing may play a role in cracking performance, and that its significance and measurement should be the subject of future research. In addition, a fundamental crack initiation and growth law that can predict the cracking performance of asphalt mixtures subjected to any generalized loading condition was developed and evaluated. The test procedures and crack growth law developed in this study provide the Florida Department of Transportation (FDOT), as well as the pavement community in general, with the tools needed to design and specify asphalt mixtures and pavements that resist cracking. It was recommended that FDOT now proceed with the development of mixture and pavement design guidelines and specifications based on these tools.