Investigation of the Performance of Steel Slag–Granite Ballast Mixture under Cyclic Loading

Abstract

In the current study, we explored the performance of steel slag ballast (SSB), granite ballast (GB), and a slag–granite ballast mixture under cyclic loading conditions using a large-scale track simulation apparatus. In addition, the single-particle crushing strength and toxicity characteristics of steel slag were evaluated. The test results indicate that the SSB particles exhibited higher crushing strength (σo) than conventional GB. In addition, the toxicity characteristics leaching procedure (TCLP) test results indicate that the leaching concentrations of all the heavy metals in the slag were below the recommended limit, except for lead, which exceeded the drinking water limit. The cyclic test results indicate that the SSB exhibited lower vertical (Sv) and lateral deformation (ld) than the GB, and that, with the increase in the proportion of SSB (PSSB) in the GB, both the Sv and ld were reduced. It was additionally found that, with an increase in PSSB in the GB, the resilient modulus (Mr), damping ratio (D), track stiffness (k), and track modulus (u) increased, whereas particle breakage (Bg/BBI) decreased. It was further observed that the extent of the sleeper (avs) and ground acceleration was lower in the SSB samples than the GB samples. Nonlinear regression models were developed to predict the vertical strain (ε1), lateral strain (ε3), Mr, and D of the slag–granite ballast mixture. A detailed analysis of the performance of the slag–granite ballast mixture, in terms of the toxicity characteristics, volumetric strain (εv), shear strain (εs), Mr, D, avs, Bg/BBI, and k, revealed that a blend of 58% SSB and 42% GB (SSB58) can be used for optimal performance. The problem of the excessive demand for conventional ballast is addressed in the current study by utilizing steel slag as railway ballast. The benefits of utilizing steel slag ballast (SSB) over conventional granite ballast (GB), in terms of lesser vertical deformation and particle degradation, are highlighted. The lower degradation exhibited by the SSB helped in reducing the frequency of ballast replacement operations, and hence the track maintenance costs. Moreover, owing to the higher specific gravity of the SSB, its lateral displacement was found to be lower compared with conventional GB, and thereby the lateral stability of the track is improved when using steel slag as railway ballast. In addition, the SSB exhibited a higher resilient modulus compared with conventional GB, implying better passenger riding comfort where the track has steel slag as the railway ballast. In addition, in bridge approaches, SSB can be mixed with conventional ballast to allow for a gradual transition from soft to stiff and stiff to soft zones.