Development and performance evaluation of sustainable polymeric composite sleepers reinforced with recycled thermoplastics and low-CaO magnesia-silicate slag

This study presents the development and performance evaluation of sustainable polymeric composite sleepers (PCS) manufactured from recycled low-density polyethylene (LDPE), polypropylene (PP), chopped glass fibers (GF), and low-CaO magnesia–silicate slag (LC-MSS), a by-product of stainless-steel refining. The structural performance and long-term fastening behavior of the PCS were experimentally investigated in accordance with AREMA and ISO 12856–2 standards. Full-scale bending tests showed that the developed sleepers achieved a modulus of rupture (MOR) of 31.4 MPa and a bending modulus of elasticity (MOE b ) of 2.2 GPa, exceeding the minimum AREMA requirements for engineered polymer composite (EPC) ties. Under rail-seat compression, the maximum elastic and permanent deformations remained below 3.31 mm and 0.93 mm, respectively. In addition, screw pull-out resistance exceeded 90 kN, demonstrating robust anchorage capacity and stable load transfer at the screw–sleeper interface under service and overload conditions. The incorporation of GF and LC-MSS effectively reduced the coefficient of thermal expansion (CTE) to 83 × 10⁻⁶ K⁻¹ , contributing to improved dimensional stability under thermal variations. The long-term anchorage durability of the fastening system was assessed through an extended 27-cycle (1080 h) thermal creep test and analyzed using the Findley power-law equation. The model predicted a 30-year creep deformation of less than 1 mm, with corresponding residual clamping forces maintained above 73 % of the initial preload. Within the scope of the adopted experimental framework, these results indicate that recycled LDPE/PP-based composites reinforced with GF and LC-MSS exhibit adequate structural performance, thermal stability, and fastening durability, supporting their potential application as low-carbon alternatives to conventional timber sleepers in railway infrastructure.