Evaluation of Hot Mix Asphalt (HMA) Fracture Resistance Using the Critical Strain Energy Release Rate, Jc

This paper addresses the development and evaluation of the critical strain energy release rate, Jc, as an indicator of HMA resistance to fracture. In this research, Jc was determined from load-deformation data of a simple three-point bending fracture test using notched semi-circular specimens. The test specimens were prepared from standard Superpave Gyratory compacted HMA samples. To evaluate the effect of the HMA material properties on the variation of Jc, thirty four mixes were brought from pavement projects across the state of Idaho. All mixes were designed and constructed in accordance to the Hveem mix design method. The mixes were made with Superpave PG-specified asphalt binders and covered wide range of aggregates. Experimental results indicated that Jc is sensitive to mix design components including the asphalt binder grade and content, and the aggregate structure. Jc was found to increase with the aggregate surface texture and angularity indices as determined by Aggregate Imaging System. It was also found that aggregates with high content of flat and elongated particles had low Jc. Finite Element techniques were used to model the test configuration and calculate the mix stiffness and relate it to Jc. It was found that as the stiffness increased the Jc increased for the investigated mixtures. Results suggest that the Jc could be used as a screening tool at the mix design stage to assess the mix propensity to fracture. Extending this test to apply cyclic loading and induce fracture under repeated loads can assess the fatigue damage tolerance of HMA.