Sustainable sleepers: recycling for railways

The industry is increasingly focusing on sustainable waste management practices, aiming to extend the life cycle of materials as much as possible. This chapter explores the utilization of three major waste materials in China—tires, glass bottles, and bamboo furniture—in the manufacturing of railway sleepers. By substituting a portion of the fine aggregate with rubber and glass sand, and incorporating bamboo as fiber reinforcement in the concrete, this study seeks to enhance the sustainability of railway sleepers. An initial study was conducted to identify optimum concrete mixtures suitable for railway sleeper production. Accordingly, recycled rubber sand (RRS) was used to replace 5%, 10%, 15%, and 20% of the fine aggregate volume with both 30# and 60# mesh sizes. Additionally, recycled glass sand (RGS) replaced up to 100% of the fine aggregate volume in varying proportions. Various percentages of recycled bamboo fibers (RBF) were also tested, constituting 10%, 15%, and 20% of the concrete volume. The mechanical properties of the resulting concrete, including compressive strength, tensile splitting strength, and flexural strength, were thoroughly examined. Subsequently, 12 concrete railway sleepers were produced using the optimal mixtures of RRS, RGS, and RBF, and their bending strengths at the middle and rail seat were tested. The findings suggest that a 20% substitution of natural sand with RGS, #60 size, along with 5% RRS and 2% RBF, yields the most favorable mixture, demonstrating compressive, flexural, and splitting tensile strengths of 84.6, 9.74, and 6.3MPa, respectively. Compared to the reference sleeper, the RGS sleeper exhibited superior bending strengths in both the middle and rail seat sections, by approximately 16% and 24%, respectively. Conversely, the reference sleeper outperformed the RRS (M60-R5) and RBF (B2) sleepers in terms of bending strength at both the middle and rail seat sections.