Stabilization of Railroad Ballast Using Polyurethane Under Various Coal Fouling Conditions

This paper presents a comparative study on the shear behavior of coal fouled polyurethane-stabilized and polyurethane-stabilized coal fouled ballast. Fresh ballast and coal fines of mean particle sizes (D₅₀) of 42 mm and 545 microns, and Elastan polyurethane polymer with a density of 1100 kg/m³ were used in the current study. Tests were conducted at normal stress (σ_n) varying from 60–120 kPa and at rate of shearing (S_r) 3 mm/min. To mimic the effect of coal fouling, a predetermined amount of coal was added that signifies a fouling level, of 30% void contamination index (VCI), in the present study. Test results highlighted that polyurethane stabilization technique enhanced shear stress of ballast. However, the coal fouling reduced the shear stress of polyurethane-stabilized and unstabilized ballast. The friction (φ) and dilation (ψ) angles of polyurethane-stabilized and unstabilized ballast were found to reduce non-linearly with an increase in σ_n. Furthermore, the values of φ and ψ of unstabilized ballast reduced from 65° to 60° and 21° to 16°, respectively due to coal fouling. The stabilization efficiency factor (S_ef), stated as the ratio of the shear stress of stabilized ballast to the unstabilized ballast, differs from 1.70 to 1.75 for polyurethane-stabilized ballast as σ_n varies from 60 to 120 kPa. Moreover, it is observed in coal fouling conditions that the coal fouled polyurethane-stabilized ballast (FPSB) shown better performance when compared to polyurethane-stabilized coal fouled ballast (PSFB).