Laboratory investigation on the cracking performance of paving polyurethane mixture using semi-circular bending test

Abstract

Polyurethane mixture (PUM) consisting of polyurethane (PU) binder and aggregates has been attracting great interest due to its high-temperature stability and mechanical strength. However, the understanding of crack resistance under ultimate load and fatigue fracture performance under repeated load of PUM is limited. Recent studies have demonstrated that the isocyanate content is strongly associated with the properties of polyurethane (PU) obtained from the chemical reaction between isocyanate and polyol. Few studies have quantified the effects of PU binder with different isocyanate contents on the crack resistance and fatigue performance of PUM. To fill this gap, this study prepared PU binders of different elongations and tensile strengths by varying the isocyanate content. The crack resistance and fatigue fracture performance of PUM were evaluated by semi-circular bending test (SCB) monotonic test at different temperatures and SCB fatigue test based on the number of cycles to fatigue failure and dissipated energy. As a comparison, the crack resistance and fatigue fracture performance of SBS modified asphalt mixture (SMAM) were also investigated. The results indicate that with the increase of isocyanate content, the elongation of PU binder decreases and tensile strength increases. The PU binder with a higher isocyanate content enhanced fracture energy, fracture toughness, and stiffness of PUM. According to the fracture energy, fracture toughness, stiffness and the number of cycles to fatigue failure, PUM outperforms the SMAM counterpart in both crack resistance and fatigue performance. As isocyanate content increases, under the same stress level, the number of cycles to fatigue failure increases, and the fatigue failure of PUM also requires more dissipated energy. Finally, the elongation correlated well with crack resistance, as they affected the fracture energy, fracture toughness, and stiffness. The number of cycles to fatigue failure correlates well with the load for different elongations.