Assessment of Steel Slag and Rubber-Coated Aggregate as Ballast Based on Model Track Tests

Abstract A series of model track tests were conducted to investigate the effect of loading frequency ( f ) on the deformation and degradation characteristics of unreinforced and geogrid-reinforced steel-slag ballast (SSB) and rubber-coated ballast (RCB) under clean and coal-fouled conditions. Test results indicated that the performance of ballast samples was significantly influenced by f and the presence of coal fines. For instance, as f increased from 10 to 40 Hz, the extent of vertical settlement ( S v ) of unreinforced SSB 50 (50% SSB + 50% granite ballast) and RCB 50 (50% RCB + 50% granite ballast) increased from 17.36 to 31.72 mm and 25.66 to 47.87 mm, respectively. The increase in loading frequency had a similar effect on the extent of lateral deformations, resilient modulus, damping ratio, and particle breakage. Similarly, with the increase in void contamination index (VCI) from 0% to 30%, the S v of unreinforced SSB 50 and RCB 50 increased from 17.36 to 19.99 mm and 25.66 to 31.84 mm ( f = 10 Hz ), respectively. However, the extent of breakage of coal-fouled SSB 50 and RCB 50 decreased, owing to the cushioning effect caused by the addition of coal. Moreover, geogrid reinforcement considerably reduced the deformation and degradation of the ballast, even at high loading frequencies and VCI values. Further, the performance of the ballast was assessed in terms of performance index ( P I cyc ), defined as the ratio of the change in volumetric strain between clean unreinforced granite ballast (GB) and the clean or fouled conditions of unreinforced/geogrid-reinforced samples to the clean unreinforced GB. The P I cyc of geogrid-reinforced SSB 50 and RCB 50 was determined to be 0.49 and 0.20 ( f = 10 Hz and VCI = 0 % ), respectively.