Aqua-thermally treated high-strength rubberized concrete railway sleepers reinforced with recycled tire steel fibers: Mechanical performance assessment and structural viability for modern railway systems

Railway sleepers are subjected to quasi-static, dynamic, and impact loading, which can accelerate cracking and premature deterioration due to the inherent brittleness and low energy absorption capacity of conventional concrete. This study proposes a high-performance rubberized concrete composite incorporating aqua-thermally treated rubber aggregates and recycled tire steel fibers to enhance the structural resilience of prestressed concrete railway sleepers. Material-level investigations revealed that high-strength concrete incorporating 10% treated rubber aggregates and 0.5% recycled tire steel fibers fully restores the compressive strength to the level of control concrete, eliminating the inherent strength losses typically associated with rubberized concrete. Furthermore, the modified composite exhibited approximately 11% and 18% higher tensile and flexural strengths, respectively, together with a 7.3-fold increase in impact resistance compared with the control concrete. Microstructural analyses using scanning electron microscopy, micro-CT, and nanoindentation confirmed improved stress-transfer mechanisms and a 2.62-fold increase in plastic energy-dissipation capacity. The proposed material was subsequently implemented in full-scale railway sleepers and evaluated under static and impact loading conditions. Modified sleepers exceeded the designed first-crack load by more than 25% at both the rail-seat and midspan regions, while exhibiting nearly 4.8-fold greater impact energy-dissipation capacity than conventional sleepers. Enhanced resistance to crack initiation and propagation was also observed under service-representative loading conditions. Additionally, RTSF-RuC sleepers sustained more than 99% of the field-based induced wheel-rail interaction repeated impact loading without forming cracks. These findings identify the proposed dual-recycled composite as a sustainable alternative for modern rail infrastructure, with significantly improved load-bearing performance, toughness, and crack resistance.