Degradation Law and Experimental Study of High- Performance Shotcrete Under the Coupling Effect of Sulfate and Chloride Salt

Shotcrete used in underground structures like tunnels is susceptible to sulfate and chloride erosion. In order to systematically study the deterioration law and mechanism of the durability of high-performance shotcrete under a salt erosion environment, the durability test of high-performance shotcrete was carried out by an indoor long-term immersion test using a clear water solution, Na₂SO₄ solution, and Na₂SO₄ and NaCl mixed solution as erosion mediums. A comparative study was conducted on the effects of different curing time, erosion time, erosion medium, and erosion direction on the physical and mechanical properties and SO₄^2- content. The microstructure was analyzed to reveal the time evolution process and mechanism of the durability of high-performance shotcrete under coupled erosion. The results show the following: (1) The mass change rate of high-performance shotcrete under the action of coupling erosion increases first, then decreases, and then increases. The compressive strength of the surface perpendicular to the jet direction is better than that of the surface along the vertical jet direction. (2) The diffusion depth of SO₄^2- along the injection direction is larger, and the content of SO₄^2- is larger at the same depth. The existence of Cl^- delays the diffusion of SO₄^2- to a certain extent. (3) In the early stage of erosion, the corrosion expansion products generated by the external SO₄^2- entering the concrete will fill the original pores and cracks, which improves the durability of the concrete. In the late stages of erosion, the accumulation of corrosion products increases, which accelerates the deterioration of its durability.