Reuse of shield slag tailing in China: current status and future opportunities

The rapid expansion of underground infrastructure in China has resulted in the generation of vast quantities of shield slag tailings (SSTs), creating significant disposal challenges. Although SSTs are often considered waste, their composition-primarily SiO₂ and Al₂O₃-makes them suitable for resource recovery in construction materials. This review critically examines the current state of SST utilization in China, focusing on two primary pathways: direct reuse (e.g., grouting materials, controlled low-strength materials, baking-free ceramics, and bricks) and calcination-based activation (e.g., supplementary cementitious materials, limestone calcined clay cement, and baked ceramics). Key findings show that SSTs can replace conventional materials at high incorporation rates (up to 80% in grouting, 60% in controlled low-strength materials, and 90% in baking-free ceramics). Calcination further enhances their pozzolanic activity and helps mitigate organic pollutants. Notably, direct reuse methods primarily employ SSTs as fillers, while calcination unlocks large-scale, high-value applications by decomposing harmful additives and improving reactivity. Economic and environmental analyses indicate substantial potential for cost savings (e.g., $17.34 billion annually through clay substitution in cement) and carbon footprint reduction (up to 30% in limestone calcined clay cement). This study highlights the novelty of SST recycling in China, bridging gaps in the global literature by consolidating dispersed research and proposing scalable solutions. Challenges such as the feasibility of low-carbon industrial calcination processes, methods to overcome blending thresholds, and durability trade-offs are also discussed, with recommendations for future research to advance sustainable SST management.