Study On Diffusion And Reaction Mechanism With Experimental Under Sulfate Attack In Cracked Concrete

Sulfate attack is a problem involving ion chemical reaction, material change and multi-physics coupling of the mechanical damage, it has been an important research in durability.There is often a lot of cracks during normal use in concrete structures like Metro and tunnels, these cracks will greatly accelerate the diffusion of sulfate ions, thereby accelerating the deterioration of the material.Therefore, with cracks in the usual subway tunnel double mixed concrete object, establish a reasonable mathematical model study of the evolution of its performance, service life prediction were materials, has great significance for the durability of the design.In this paper, summarized the law of ion diffusion in the cracks, and suggest a common expression in fractures ion diffusion coefficient.Establish a simplified 2D diffusion model of chloride ion in concrete cracks and solved by COMSOL MULTIPHYSICS commercial finite element software, and verify the correctness of the general expression of the diffusion coefficient. The results showed that the crack width wider, the greater the ion concentration; deeper crack depth, the smaller the ion concentration.Based on chemo-mechanic coupling mechanism, established the chloride ion diffusion model under Sulfate in the cracked concrete and solved by MATLAB programming, verify the sulfation force coupling mechanism is correct.Based on chemo-mechanic coupling mechanism, established the 2D diffusion equation sulfate concrete and solved by finite difference method, the final test were compared to sulfate attack validation. Solving found that changes in ion concentration gradient from outside to inside, top edge, center lowest ion concentration in the erosion of a certain time to maintain homeostasis.