Triaxial testing of new and degraded ballast under dry and wet conditions

While many studies focused on both new and fouled ballast behavior due to contamination by external fouling agents, far fewer studies have focused on the mechanical breakdown of crushed ballast stones and the behavior of used ballast due to gradual aggregate degradation. This paper presents triaxial test results conducted on both new and degraded limestone ballast samples to investigate deformation trends and evaluate effects of varying moisture contents. Based on the limited experimental results, degraded ballast samples in dry conditions and typically at a denser state compared to the new and clean ballast did not result in significant strength loss. In most cases, the degraded ballast yielded even higher strengths, which is different than reported in previous studies focused on testing contaminated ballast. However, when subjected to repeated load cycles, degraded ballast specimens exhibited much higher permanent deformation accumulations. When moisture was introduced, the degraded ballast showed significantly larger permanent deformations and strength losses compared to the results observed from dry testing conditions. Negative impacts of moisture on degraded ballast were generally similar as on the contaminated ballast, but the mechanical property changes were more abrupt mainly due to size reductions in coarse aggregate particles and the aggregate skeleton itself.