科研之友
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摘要
Salt lake is widely distributed in Western China. The high concentrations of chlorine salt, sulfate, and magnesium salt in soil and underground water are the leading causes to the deteriorated performance of lining shotcrete and corrosion of reinforcement. This study aims to investigate the durability performance and deteriorated rules and mechanism of shotcrete lining in salt lake corrosion environment by using dry-wet (D&W) alternate method for simulating the corrosion mode of tunnel lining. A shotcrete durability experiment is performed in 5% Na2SO4 + 5% MgSO4 + 3.5% NaCl solution. Relative dynamic elastic modulus, mass change, and relative compressive strength are measured. Thereafter, the mineral composition and microscopy of corrosion products and the air-void structure parameter and ion content of water-soluble sodium, chloride, and calcium ions; acid-soluble sulfate ion; and pH value of pore solution are tested using X-ray diffraction, thermogravimetric-differential scanning calorimetry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, RapidAir 457, and electrochemical method. @@@ Acid solubility sulfate content clearly increased with the D&W cycle, and water-soluble chloride and sodium content slowly increased. Meanwhile, water-soluble calcium and concrete pH value decreased. The combination of the expansion stress and crystallization pressure from thaumasite, brucite, gypsum, ettringite, and crystallized salt enlarged the air-void number and air content in shotcrete. Moreover, web crack formation caused deterioration of the physical and mechanical properties of shotcrete. Meanwhile, normal concrete was damaged by macrocracks connected with air void and microcracks, thereby creating crystallization pressure. Drawing stress between steel fiber and shotcrete could evidently absorb the expansion stress and crystallization pressure. Consequently, steel fiber could improve shotcrete corrosion resistance.
