Effect of low dosage fiber reinforcement on cracking performance of asphalt concrete

Fiber reinforcement is one of the methods used to improve cracking resistance of quasi-brittle materials such as asphalt concrete (AC). Despite the widespread use of fibers in AC, there is a lack of fundamental understanding of fracture behavior of fiber reinforced asphalt concrete (FRAC). The main goal of this research is comprehensive fracture characterization of low dosage applications of two synthetic fibers (polyethylene-aramid and nylon) and understand the performance bias of low dosage fiber reinforcement at mixture level in different test conditions. Two laboratory prepared mixtures (fine and coarse-graded) were designed with consistent volumetrics. Two crack mouth opening displacement (CMOD) – controlled experiments (SCB-CMOD and DCT) were performed to facilitate a controlled crack propagation at low and intermediate temperatures. Alternative load-line displacement (LLD) control cracking tests (I-FIT and IDEAL-CT) with different geometries, testing parameters, and loading modes were also evaluated. It was observed that the mixes with nylon fibers had a distinctive and better fracture response in all of the experiments. Some improvements were observed with aramid fiber configuration dependent on the test performed and mixture type. The key test features that resulted in more distinction between the low dosage fiber mixes and the control appeared to be ligament length, affected damage area, and cracking patterns observed in the experiments. The tests with larger ligament length (i.e., larger affected damage zones) were sometimes visible with more tortuous cracking patterns with many branches resulted in more consistent and noticeable outcomes with the fibers. Further research is needed to identify potential test bias and develop an ideal test protocol and test geometry that can objectively evaluate the performance of low dosage fibers.