Investigation on properties of cold recycled asphalt mixtures reinforced with polypropylene fibers

Despite substantial environmental and economic benefits, cold recycling of asphalt pavements is not common due to some poor field performance reports. This study investigates the effect of fiber reinforcement on the performance of cold recycled mixtures. For this purpose, cold recycled mixtures were reinforced using polypropylene fibers at two different lengths and three different contents. Indirect tensile strength, IDEAL-CT, and semicircular bending tests were carried out to find the optimum length and content of the fiber. The effect of cement on performance of fiber reinforced mixtures was also evaluated. The results show that although the use of polypropylene fibers reduces the wet strength by up to 54%, it can increase the dry strength by up to 39%. The results also indicate a significant improvement in fracture indices obtained from IDEAL-CT and SCB tests in the presence of fiber. Crack tolerance index was 3.5 times and flexibility index was 2.8 times higher at the optimum fiber content and length compared with the control mixture. It was also concluded that the addition of cement to fiber reinforced mixture can eliminate the adverse effect of fiber on moisture sensitivity, while maintaining the fracture properties similar to the control mixture. The study results show that the combined use of fibers and cement can lead to an economical cold recycled mixture with reduced emulsified asphalt content and improved mechanical properties.