Experimental investigation on calcium dissolution performance of shotcrete with different waterproofing agents

The crystalline blockage of tunnel drainage pipes poses a common challenge to tunnel engineering, particularly in regions with abundant groundwater and severe ion erosion. Based on the design of concrete mix proportion, this paper improves the calcium ion erosion resistance of shotcrete by adding permeable crystalline sodium methyl silicate waterproofing agent and silane waterproofing agent. Concurrently, the mechanical properties and microscopic characterization of waterproofing agent concrete are carried to determine the optimal dosage for practical engineering applications. The experimental results reveal that the sodium methyl silicate waterproofing agent has minimal impact on the calcium ion dissolution resistance of shotcrete. In contrast, the silane waterproofing agent significantly enhances the calcium dissolution performance of shotcrete, and the optimum dosage is identified as 0.4%. During long-term maintenance, the silane waterproofing agent proves more effective in improving the compressive strength of shotcrete compared to the sodium methyl silicate waterproofing agent, showing an increase rate exceeding 20%. Both waterproofing agents contribute to the enhancement of the tensile strength of shotcrete, and the enhancement effect is consistent with the compressive strength. The permeable crystalline waterproofing agent expedites the cement hydration process, resulting in the formation of higher-density calcium silicate hydrates (C-S-H) gel and ettringite (AFt). These substances fill the pores of shotcrete leading to a more compact internal structure. The calcium ion dissolution and mechanical strength test results collectively validate the superior effectiveness crystallization prevention of aterproofing agents . This research provides valuable insights for addressing the tunnel crystallization phenomenon caused by the calcium dissolution.