Laboratory evaluation of the effect of microfibers on the low-temperature cracking performance of grouted macadam mixtures

Abstract

Grouted Macadam (GM) mixtures are a composite of bituminous and cementitious phases used as pavement semi-flexible overlays because of their high static bearing capacity and rutting resistance, good durability, and proper resistance to chemical attacks and fossil fuels. However, these mixtures do not have good performance at low temperatures. Reinforcement by fibers is a popular method to improve the performance of asphalt and concrete mixtures and has the potential to be used to reinforce GM mixtures. This study aims to reinforce both bituminous and cementitious phases of GM mixtures using glass based (Microcorta) and polypropylene based (PP) fibers, respectively. The bituminous phase of the first group of the GM mixtures was reinforced with 0.2, 0.4, and 0.6 vol% of glass microfibers (MC). In addition, 0.2, 0.3, and 0.4 vol% of PP fibers were used to produce the cement grout of the second group of GM mixtures. In the next step, the performance of each group was compared with that of the fiber-free samples using a three-point bending test (TPB) and low-temperature indirect tensile test (IDT). Based on the obtained results, GM mixtures’ best low-temperature performance in both IDT and TPB tests was obtained for mixtures containing the highest percentage of fibers (0.6% of MC and 0.4% of P.P fibers). Also, it was observed that the reinforcement of the bituminous phase increased the fracture strain tolerance (FST) in the TPB and IDT tests by 66.19% and 25.01%, respectively, compared to fiber-free samples. Moreover, using fiber-reinforced cement grout has been able to enhance the FST index in the TPB and IDT tests by 91.87% and 30.9%, respectively, compared to fiber-free samples. Overall, the results demonstrate that the reinforcement of both bituminous and cementitious phases of GM mixtures by microfibers can help improve their ability to resist low-temperature cracks.