Low-carbon backfill grouting materials for shield tunneling: a mini review

In response to the growing low-carbon demand for urban shield tunneling, this study presents a mini review of low-carbon backfill grouting materials, focusing on their material taxonomy, performance mechanisms, and engineering adaptation pathways. The review systematically summarizes recent advances in three major categories of sustainable grouts: alkali-activated grouts (AAG), asphalt-related composite grouts, and shield tunnel spoil (STS)-based recycled materials. Despite significant progress, persistent challenges remain in long-term performance evaluation, mix design standardization, and adaptation to complex hydrogeological conditions. Future research should integrate material innovation, multi-source solid waste synergy, and digital construction technologies to establish a performance-driven, low-carbon-oriented framework for grouting materials. This review provides holistic insights into the sustainable development of shield tunneling materials and promotes the transition toward more environmentally friendly, low-carbon, and resilient underground infrastructure systems.