Reusing Life-Expired Railway Ballast: Laboratory Testing, Shape Analysis, and Petrographic Evaluation

During its service life, railway ballast degrades. Individual grains are abraded, asperities may break off, and the assembly loses performance as the finer material created progressively fouls the assembly. The causes of this are the repeated cyclic loading from passing trains and the major damage caused to ballast by tamping operations to restore track geometry. Eventually the ballast bed requires complete replacement, and recovered trackbed material is disposed of as waste or downcycled. However, modern ballasts often are formed from stronger parent rocks than in the past, and a proportion may retain sufficient characteristics for reuse. This paper investigated the reuse of recovered life-expired ballast. A series of tests using fresh and reused ballast was carried out using the Southampton Railway Testing Facility (SRTF) and a large triaxial testing apparatus to compare performance. The properties of individual ballast grains were characterized in terms of their shape and petrographic make up. The results show that the type of recovered life-expired ballast used in this study has good performance and similar strength to fresh ballast despite having reduced surface roughness. The petrographic analysis showed that a majority of the recovered ballast was formed of granite, with a significant minority of basalt. These findings may be in contrast to those of some previous studies in which different life-expired rock sources were used, and highlights the importance of the source material.