Engineering properties and applicability of a novel alkali-activated industrial waste-based backfilling grouts in shield tunnels

Cement-based grout is widely used for backfill grouting in shield tunnels, but traditional grout leads to high carbon emissions and poor stability in the face of water-rich strata. This study utilizes industrial wastes FA, GGBS, and SF to completely replace cement. An alkali-activation method is employed to prepare a novel backfilling grout. The influences of GGBS content, SF content, modulus of the alkali-activated solution (MAAS), alkali content, and liquid-to-solid ratio (LSR) on fluidity, bleeding rate, stone rate, setting time, compressive strength, and water absorption, are investigated. Results show that increasing the content of GGBS, SF, alkali and MAAS, or decreasing LSR can enhance the stability, mechanical properties and impermeability. Higher GGBS, SF, and alkali content, or lower MAAS and LSR can facilitate timely setting and hardening of the grout to control ground settlement, but negatively affect fluidity. Lastly, the optimal ratio of novel grout is obtained for Nanning’s geological conditions.