Impact loads induced by track irregularities or wheel defects during train operation accelerate ballast degradation and threaten track performance. To investigate the mitigating effect of crumb rubber (CR) on ballast degradation, impact tests were conducted on ballast samples mixed with different CR volume contents (0%, 10%, 20%, and 30%) using a custom drop-weight impact apparatus. Post-impact analyses evaluated cumulative settlement, particle size distribution evolution, and ballast particle breakage. Test results demonstrate that: CR inclusion nonlinearly reduces cumulative settlement of ballast, with mitigation efficiency increasing proportionally to CR content; Ballast breakage decreases sharply at 10% CR due to energy absorption, but exhibits transitional behaviour at 20%–30% CR: fracture reduction continues while abrasion intensifies, ultimately stabilising with abrasion as the dominant failure mode. Ballast breakage index confirms diminishing marginal returns in breakage reduction beyond 20% CR. Considering incremental costs and drainage constraints, 20% CR content provides optimal equilibrium between impact energy attenuation and long-term ballast stability.
Chen et al. (2026) studied this question.