Study Of Erosion Ions Transport In Concrete Based On Meso Numerical Simulation

In the actual service process,the coastal concrete structure not only suffers from the coupling erosion of chloride,sulfate and other ions,but also bears the external load.Generally,the corrosive substances enter into the concrete from the connective pores,and react with the hydration products of cement or cause corrosion of steel bars,which leads to the decrease of durability and service life of concrete.The second Fick law is used to describe the process of corrosion ions entering concrete.The influence of temperature,relative humidity,pore water saturation and other factors are considered by modifying the diffusion coefficient,and a consumption term is added to describe the chemical reaction consumption of corrosive substances.In this paper,the meso level concrete was taken as the research object.Considering the influence of complex environment,the single factor erosion mechanism of chloride and sulfate,the coupling erosion mechanism of chloride sulfate and load sulfate were studied.The ion erosion model was established in turn,and the influence of aggregate on ion transport was discussed and analyzed.The main research contents are as follows:The effects of dilution effect,distortion effect and interfacial transition zone effect on the diffusion coefficient of concrete were discussed,and the ion diffusion model of interfacial transition zone was established.According to the erosion diffusion mechanism of chloride and sulfate in concrete,an erosion model considering aggregate effect was established.The analysis results show that the model calculation results are basically consistent with the experimental results in the literature.The ion diffusion coefficient in concrete is mainly determined by the diffusion coefficient of cement mortar,the diffusion coefficient of interfacial transition zone,the volume fraction of aggregate and the volume fraction of interfacial transition zone.The effective diffusion coefficient,initial aluminate content and ion boundary concentration have significant effects on the results of sulfate attack.In view of the limitation of the simulation method of the real thickness of the interface transition zone,the ITZ boundary research method was proposed.Based on the single erosion ion model,the coupling transport mechanism of chloride sulfate in concrete was clarified,and the coupled erosion model was established.The analysis results show that the model calculation results are in good agreement with the experimental data in the literature.There are complex interactions between ions in the coupled transport process,which reduces the chloride ion transport performance in concrete.The key parameters of the model are:aggregate content,ITZ diffusion property and initial porosity.The relationship between the load effect and the current porosity of concrete was quantified,and the load effect was equivalent to the effect of porosity change on sulfate corrosion.Based on the theory of elasticity and homogenization technology,the internal expansion strain caused by ettringite was equivalent to the macro strain,and the sulfate corrosion model in bearing concrete was established by linear superposition with load tensile strain.The analysis results show that the simulation method is effective by comparing with the experimental data in the literature.With the increase of load level,the accelerated damage mechanism becomes more obvious.In general,the concentration of sulfate ion in concrete increases and the dynamic elastic modulus degrades gradually.