A novel laboratory investigation to characterize the mechanical behaviors of polyurethane-ballast bonds under complex stress states

Abstract

The polyurethane has been successfully applied to reinforce the railway ballasted track and the bonding properties of the polyurethane to ballast particles have significant effects on track performance. However, the mechanical behaviors of the polyurethane-ballast bonds(PBBs) haven’t been reported leaving the particle scale mechanism of the polyurethane reinforcement still unclear. A novel laboratory experimental method was developed in this paper to characterize the mechanical behaviors of the PBBs. Using standard test specimens with various specimen size and bond thickness, a series of laboratory tests were conducted to measure the stress–strain responses of the PBBs under tensile, compressive and shear loadings. The measured results show that the stress of a PBB increases nonlinearly with its strain when it subjects to uniaxial tensile or compressive loads. The test results also validate that the strength envelope of a PBB follows the linear Mohr-Coulomb criterion. A modified parallel bond model was proposed to predict the nonlinear stress–strain behaviors of the PBB with high accuracy. Furthermore, it is found that the bond thickness has distinct effects on the tensile and the cohesion strength of the PBB but negligible effect on its friction angle. The initial tangent elastic modulus of the PBB increases approximately linearly with the increase of the bond thickness. The experimental method, results and the modified bond model introduced in this paper are very helpful for the performance evaluation and the numerical simulations of polyurethane reinforced ballast.