Calcium Ion-chloride Ion Transport Model And Experimental Study In Cement-based Materials

The cement-based materials which immersed in water environment for a long time,calcium ions in the pore solution of the material will diffuse into the external environment because of the concentration gradient effect,which resulting in calcium hydroxide dissolution and CSH gel decalcification,then occurrence of corrosion damage.If there is chlorine,salt and other erosive substances in environmental water,chlorine ions and other harmful substances will different from the outside to the inside of the material.For the concrete structure in the environment of chlorine salt water,calcium chloride corrosion and erosion will seriously affect the durability of materials;reduce the service life of the structure.Therefore,study on the erosion mechanism of cement based materials durability degradation coupling in corrosion and chloride salt,a calcium ion and chlorine ion coupled transmission model is of great significance for the prediction of service performance of concrete materials and structures.(1)Based on the theory of the erosion mechanism of calcium and solid-liquid balanceent connection and the porosity model,as well as variation of diffusion coefficient,the ductile corrosion model is established.Then the corrosion experiment of cement paste slice in 6mol/L NH4C1 solution was carried out to proved the rationality of the ductile corrosion medel.(2)Chloride corrosion coupling effect of cementitious materials under the degradation,the erosion mechanism of calcium and chloride corrosion theory based on saturated cement-based materials of calcium ion and chloride ion coupled transmission model theory,experimental studies and numerical analysis.The main contents and results are as follows.(3)The solid-liquid equilibrium relationship between cement hydration mechanism and dissolution of calcium in the process of cement-based materials based on the porosity evolution model,the diffusion coefficient changes,established the cement base material of calcium dissolution model under the environment of water immersion,and corrosion tests of cement paste sheet in 6mol/L ammonium chloride solution was carried out by the correctness of the model verification results show that the calculation results of the model test and the experimental results are in good agreement.(4)According to Fick's law of diffusion and adsorption of cementitious materials on the chloride ion binding mechanism,a one-dimensional chloride saturated cement-based material diffusion equation,combined with the Newton diffusion law,calculation method of push surface chloride ion concentration derived cement-based materials,and the simulation results compared with the results of the show the calculation results,the surface chloride concentration are in good agreement with the experimental results.Based on calcium dissolution model and chloride ion diffusion model is established on the comprehensive consideration of the dissolution process of chloride ion diffusion coefficient,transmission porosity,binding effect and adsorption of cementitious materials on the chloride ion,calcium ion and chloride ion is established coupled transport model of saturated cement-based materials,and the the coupled equations in detail is solved by the finite-difference method.(5)The cement mortar specimens in lmol/L NaCl 1mol/L solution,NH4C1 solution,lmol/L,NaCl+3mol/L corrosion test in NH4NO3 solution,using phenolphthalein titration method,saturated weighing method,chlorine ion titration method for different corrosion periods of the mortar specimen corrosion depth,porosity,content of chloride ion,the experimental results show that the different soaking solution in cement mortar specimens corrosion depth and the square root of time is linear,which soaked in the solution(NH4NO3+NaCl)cement mortar specimens corrosion depth,porosity,maximum chloride content,cement mortar was soaked in NaCl solution in the specimen corrosion depth,porosity,the minimum content of chloride ion.(6)The numerical simulation of the coupled transmission process using Matlab program on corrosion and chloride corrosion coupling effect of cementitious materials under the calcium ion and chloride ion,and compared with the corrosion test results,the results show that the simulation results are in good agreement with the experimental results,and on this basis,the analysis model of the position time step.Step size,material ratio of water to cement ratio,influence of dissolution parameters on the calculation results.