A Comparative Study of New Ballast and Recycled Ballast Generated from Various Maintenance Activities

Railroad ballast performance is influenced by aggregate type, geological origin and mineralogy, gradation, and particle shape. As ballast ages, it gets progressively fouled with finer materials generated from particle breakage and abrasion, which may reduce its ability to drain water, cause rapid and excessive settlement, and reduce lateral stability. Maintenance operations including tamping, cleaning and removal, and undercutting are scheduled based on degradation level to improve ballast condition and mitigate related track geometry defects. In this study, ballast materials were studied both as fresh clean ballast and at different degradation levels with recycled ballast collected from revenue service sites after maintenance activities. (1) new or clean ballast, (2) fouled or used, (3) screened recycled (fouled ballast disregarding materials passing the 3/8-in. or 9.5 mm sieve), and (4) a blend of 30 % screened recycled and 70 % clean ballast were evaluated. Various characterization tests were conducted including morphological characterization, mechanical breakdown and degradation performance, drainage property, long-term settlement potential, local shear waves or modulus, and load bearing and lateral stability. Additionally, a 50 % screened recycled and 50 % clean ballast samples were evaluated in terms of lateral stability to investigate performance with greater portion of rounded particles. Results showed that although removing fines from fouled ballast can maintain long-term settlement performance, the lateral stability will decrease. Nevertheless, reusing up to 30 % of screened recycled ballast materials can maintain settlement and lateral stability performance. The results provide guidance about performance trends of reclaimed ballast after different maintenance activities with the overall goal to maintain a safe and reliable ballasted rail network operation. Future research should focus on evaluating mechanical behavior trends of recycled ballast and its blends with virgin material at varying moisture levels.