Deformation and degradation behaviour of coal-fouled tyre chips intermixed steel slag ballast under cyclic loading

Steel slag and tyre chips are two waste products with potential for sustainable use in railway tracks. While the previous studies have primarily focused on the benefits of utilizing steel slag as railway subballast, yet its suitability as railway ballast with and without tyre chips (TC) has not been comprehensively investigated. Moreover, the possible effect of coal fouling on the performance of TC-intermixed steel slag ballast is yet to be studied. Therefore, the current study assessed the influence of TC on the performance of slag-granite ballast mixture under coal-fouled condition using large-scale track simulation test (TST) and constant-head permeability apparatus. TST results indicated that vertical and lateral deformations of ballast increased, while the track stiffness ( k ) and ballast breakage index ( BBI ) decreased with the increase in proportion of tyre chips. The threshold content of tyre chips to be mixed with steel slag ballast (SSB) is identified as 10%. The study further established that the addition of coal leads to an increase in deformations, while reducing BBI of TC intermixed slag-granite ballast. Moreover, the addition of coal causes a significant reduction in hydraulic conductivity of the TC intermixed ballast. Further, the critical value of void contamination index is determined to be 25%.