Internal Curing for Tunnel Self-Compacting Concrete Using Pre-Soaked Coal Gangue: A Promising Way for Spot Utilization of Coal Gangue

Coal gangue (CG) can be a potential aggregate for concrete production considering its huge production. However, its porous structure and high water absorption significantly impact the workability of concrete, restricting its comprehensive utilization. This paper proposed a straightforward pre-soaking technique for CG, where the pre-soaked CG (PCG) is partially substituted for natural sand to provide internal curing effect for self-compacting concrete (SCC) for the paving of coal mine tunnel roads. The effects of pre-wetted coal gangue on the fluidity, internal relative humidity (IRH), autogenous shrinkage, compressive strength, microstructure, micromechanical properties, and chlorine resistance of concrete were investigated. Experimental results revealed that the incorporation of PCG into SCC not only enhanced the fluidity but also maintained a higher internal relative humidity, thereby mitigating the autogenous shrinkage of SCC by 25—60%. The released water from PCG facilitated the hydration of cement; and the precipitation and accumulation of more hydration products densified the microstructure and enhanced the ITZ between aggregates and matrix, resulting in enhanced micromechanical properties of SCC. Consequently, the 28d compressive strength of SCCs was increased by 1—10.6% and the chlorine ion resistance was enhanced by 11.2—27.5% by incorporating 10—40% PCG compared with the blank one.