Chloride diffusion of shotcrete lining structure subjected to nitric acid, salt–frost degradation, and bending stress in marine environment

Abstract

The chloride diffusion of shotcrete lining at the middle and passageway of submarine tunnels subjected to chloride attack, combined action of NxOy from automobile exhaust and chloride attack, salt–frost degradation, and surrounding rock stress was investigated using 3.5%NaCl and HNO3+3.5%NaCl solution immersion method, accelerated salt–freezing-thawing method, and spring four-point bending loads method, respectively. Chloride content in shotcrete was measured using solid–liquid extraction and potential method. Meanwhile, the influence of chloride diffusion on nitric acid attack, salt–frost deterioration, bending stress, and shotcrete mixture parameters were analyzed. Nitric acid attack, salt–frost degradation and bending stress accelerated chloride migrate into shotcrete. When immersed in NaCl and HNO3+NaCl solution, shotcrete with low water–binder ratio and high steel fiber content had lower chloride content. With the increase in fly ash replacement, the chloride content decreased initially and then increased rapidly. Under salt–frost degradation, the shotcrete with low water–binder ratio and fly ash replacement had better chloride diffusion resistance. The distribution of chloride content in concrete conformed to Fick's second law. The chloride diffusion model was established based on the temperature of environmental and humidity of concrete, exposure time to solution, mixture parameters of shotcrete, nitric acid attack, salt–frost degradation, and bending stress.