Laboratory investigation of stone matrix asphalt modified with SBS polymer and C25 fiber in using the semi-circular bend geometry (SCB) and moisture susceptibility

Abstract

Asphalt mixtures are the ultimate layer of flexible pavements and are directly affected by the damaging effects of weather conditions and stresses caused by traffic loads. Therefore, using a reinforcing agent to improve mechanical and functional properties of asphalt mixtures seems reasonable. The purpose of this study is to investigate the effect of this type of composite fibers on some properties related to fracture mechanics such as plasticity, fracture energy, and the impact of loading rate in this field, and compare it with SBS polymer asphalt and its effect on moisture susceptibility test on Stone Matrix Asphalt (SMA), and compare it with SBS polymer asphalt and non-fibrous and non-polymeric SMA, and examine the extent of the impact of this type of fibers and polymers in composite form together on asphalt properties. In this research, C25 composite fibers were added to SMA mixture, in specific but different ratios, to improve asphalt mixture performance. C25 fibers are a pellet blend consisting of 75 wt% Arbocel cellulose fiber and 25 wt% Fischer Trapsch wax (Sasobit). Moisture susceptibility tests were conducted on original, SBS polymer and C25 fiber mix samples, and their results were compared. The semi-circular bending test was also used for the first and second fracture modes at 25° C for SBS polymer and C25 fiber samples. The results show that, in terms of indirect tensile strength, the highest strength was found for the mix with 0.4% of C25, which improved the parameter by 38% in comparison with dry unmodified sample, and by 116% in comparison with saturated unmodified samples. In drain down test, with increased amount of fiber, the drain down of bitumen decreased, and in semicircular bending test, at both 90° and 45° cracks, the fracture energy of the samples containing 0.4% fibers improved compared to the samples containing SBS polymer. Besides, the plasticity of the samples was relatively weaker in C25-fiber samples in 90° and 45° cracks than that of SBS polymer samples. At 45° crack, with increased loading speed, the plasticity of the fibrous samples decreased but in SBS-polymer samples, the parameter increased.