Ion diffusion in shotcrete lining under compound salt corrosion #br#
environment saline soil in Northwest China
Wang Jiabin1 Zhang Kaifeng2 Hou Zeyu1 Niu Ditao3
1. Xi’an Technological University, Xi’an 710021,China; 2. China West Construction North Co.,Ltd.,
Xi’an 710065,China; 3. State Key Laboratory of Green Building in Western China, Xi’an 710055,China
Abstract：Saline soil widely distributes in Northwest China. Aggressive ions can diffuse into shotcrete lining, and after a sequence of physical and chemical reactions, corrosion products with the characteristics of high solubility, expansion and non-gelling are produced, which destroys the microstructure of shotcrete and leads to the degeneration of the durability of lining structure. The durability of shotcrete exposed to compound salt was tested under drying-wetting cycles to simulate the environment of Northwest China. Furthermore, the corrosive medium of 5%Na2SO4+5%MgSO4+3.5%NaCl (mass ratio) solution was used to simulate the composition and content of aggressive ions in saline soil and the underground water, and the experiments on the durability of compound salt corroded shotcrete were carried out for measuring the pH value, the contents of water-soluble Cl-, SO 2-4 and Ca2+ and the content of acid-soluble SO 2-4. The results show that with the increase of drying-wetting cycles, the pH value and the content of water-soluble Ca 2+ of shotcrete decrease, while the contents of water-soluble Cl- and SO 2-4 and the content of acid-solubleSO 2-4 increase. The diffusion of Mg2+ into shotcrete may result in the evident decrease of the pH value of corrosion zone. However, the pH value quickly increases and then remains stably with the depth. The diffusion of Cl- decreases the content of acid-soluble SO 2-4, while the diffusion of SO 2-4 accelerates the decrease of the pH value and the content of Ca2+, and to some degree promotes the increase of Cl- content. Meanwhile, the water-binder ratio, fly ash replacement ratio and steel fiber content may significantly affect the diffusion of ions. The diffusions of water-soluble Cl- and acid-soluble SO 2-4 into shotcrete conform to the Fick's second law, and the diffusion model of ions considering the mix-proportion parameter of shotcrete was established.
