Durability degradation of lining shotcrete exposed to compound salt
Wang Jiabin1 Niu Ditao2,3 He Hui1 Wang Bin1
1. Xi’an Technological University, Xi’an 710021, China;
2. College of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China;
3. National Key Laboratory of Green Building in West China, Xi’an University of Architecture and Technology, Xi’an 710055, China
Abstract：Salt lake is widely distributed in Western China. The high concentrations of , , and Cl in the soil and underground water are the major reasons leading to the performance degradation of lining shotcrete. In order to study the durability degradation and corrosion mechanism of lining shotcrete exposed to compound salt, the durability experiment is carried out in the solution of 10% Na2SO4 and the mixed solution of 5%Na2SO4-5%MgSO4-3.5%NaCl using the dry-wet (D&W) cyclic method. Physical and mechanical property degradation rate of shotcrete exposed to compound salt is slower than that of shotcrete exposed to sulfate, due to , , and Cl reacting with portlandite and aluminum phase which can form brucite, gypsum and Friedel’s salt. The destruction form of shotcrete exposed to sulfate appears to be peeling off of surface cement mortar and aggregate, while the one of shotcrete exposed to compound salt appears to be net-like microcracks on the surface and eventually appears to be fractured. Based on analysis of the mineral composition and microstructure of corroded shotcrete, it is found that ettringite and gypsum are the main product of sulfate corroded shotcrete. However, the products of compound salt corroded shotcrete are complicated and mainly include thaumasite, brucite, gypsum, ettringite, magnesium silicate and crystal salt. Sulfate ion content of shotcrete exposed to sulfate is higher than that of shotcrete exposed to compound salt, but pH value is lower.
