Influence of liquid accelerators on shotcrete in karst area tunnels

Tunnel constructions built in karst areas are liable to calcium leaching, which can lead to CaCO3 deposits in tunnel drainage pipes and water gutters, resulting in the blockage of tunnel drainage systems. This research aimed to analyze the influence of liquid accelerators on shotcrete in karst area tunnels. To achieve this, the present study investigated the influence of accelerator type and the karst water environment on the degradation behaviors of shotcrete. More specifically, the calcium leaching processes of hardened cement pastes incorporated with various liquid accelerators were analyzed, and the tunnel drainage system blockage mechanism was expounded in terms of shotcrete lining. The results showed that the compressive strength of shotcrete decreased most significantly in a karst water environment, while the mass of shotcrete decreased most significantly in a flowing water environment. The shotcrete combined with an aluminum sulfatebased alkali-free liquid accelerator performed best in the attack test, and its maximum compressive strength decreased by only 0.33%. The accelerator can change the composition and microstructure of cement hydration, thus altering the deterioration resistance of shotcrete. In terms of shotcrete lining, calcium leaching can increase the pH value and calcium ion concentration of groundwater, resulting in the formation and crystallization of CaCO3.