Deformation properties and performance evaluation of reused ballast with waste tire-derived aggregates

The present study evaluates the shear strength characteristics, deformation properties, and degradation behavior of limestone-based reused ballast (RB) material by mixing crumbs of waste tire-derived aggregates (TDA), focusing on its suitability for railway infrastructure. Conventional large-scale direct shear tests and novel large-scale cyclic simple shear tests were performed to investigate the effects of tire-derived aggregate (TDA) content, with particle sizes varying between 22.4 mm and 50 mm. The results indicate that adding 5 % by the mass of TDA slightly reduced the friction angle from 46.6° to 44.5°, which is not a significant change compared to RB. However, increasing the TDA content to 10 % led to a notable decrease in the friction angle to 41°, highlighting the significant impact of higher TDA content on the shear strength behavior. Further, incorporating 5 % TDA improved the shear modulus and damping ratio relative to RB, which is attributed mainly to the similar larger particle sizes (22.4–50 mm) of TDA. Conversely, at 10 % TDA content, reductions in both shear modulus and damping ratio were observed. The ballast breakage index (BBI), evaluated through cyclic simple shear tests, showed a significant decrease from 15 % for RB to 9.5 % for the ballast sample containing 5 % TDA. Additionally, increased TDA content enhanced material durability, reducing Los Angeles abrasion (LAA) losses from an initial 33.5 to under 30 % at 5 % TDA. These findings demonstrate that incorporating 5 % by mass of TDA into RB material is optimal for enhancing deformation characteristics and reducing ballast degradation while maintaining adequate shear strength. This sustainable approach facilitates the recycling of waste materials, promotes a circular economy, and helps maintain safe and stable railway track conditions.