Effect of Ceramic Fibers on the Thermal Cracking of Hot-Mix Asphalt

Abstract

Thermal or low-temperature cracking is caused by extremely cold weather or temperature cycles in cold climates. This distress can be controlled by, among others, bitumen modification. In light of the positive performance of natural and synthetic fibers in previous studies, this study investigated the effect of ceramic fiber, a low-cost and available mineral fiber, as a bitumen modifier on the low-temperature cracking potential of asphalt mixtures. Bending beam rheometer (BBR) and semicircular bending (SCB) tests were performed to evaluate the rheological properties of bitumen and low-temperature performance of asphalt mixture, respectively. In addition, direct tensile strength tests using the pull-off method for cohesive failure and adhesive failure conditions, as well as thermodynamic theory based on the surface free energy (SFE) method were used to determine the mechanism of impact of ceramic fibers on bitumen and asphalt mixture properties at low temperature. The results indicated that the application of ceramic fibers up to 0.4% by weight of bitumen reduced creep stiffness and increased m-value, thereby making the rheological properties of bitumen suitable for one grade lower than the control bitumen. The results of the SFE method demonstrated that the application of ceramic fibers increased the acidic component and decreased the total SFE of the control bitumen, thus increasing the free energy of adhesion in samples with both acidic and basic aggregates. Also, bitumen modification increased the nonpolar SFE, and consequently increased the total SFE, thereby improving bitumen resistance to cohesive failure. The results of the pull-off test at the thick and thin bitumen film conditions indicated that the application of ceramic fiber enhanced the resistance to cohesive and adhesive failure. Statistical analysis also revealed that thermodynamic variables played an effective role in the type of failure. Based on the results of the SCB test parameters, the use of ceramic fiber, especially up to 0.4% by weight of bitumen, improved all three parameters of load peak, fracture energy, and fracture toughness, thus decreasing the potential of low-temperature cracking in samples made with the modified bitumen. Also, based on the statistical analysis, the performance parameters of the asphalt mixture against low-temperature cracking were efficiently dependent on the thermodynamic variables obtained from the SFE components of bitumen and aggregate.