Effect Of Applied Voltage On Chloride Ion Binding Behavior And Microstructure Of Cement Paste

The corrosion caused by chloride ions is the main factor of the failure of concrete structure. The resistance to chloride ion permeation resistance of concrete is an important evaluation index of its durability. In the actual life, the external chloride ion penetrate into concrete by diffusion, horizontal convection and capillary adsorption, and the concrete structure is destroyed after the concentration of chloride ions of the steel bar surface reaches a certain concentration. The method of natural diffusion and electricity accelerated migration was used to evaluate the resistance of concrete to chloride ion penetration. The former can reflect the tr ansmission of chloride ion in concrete, but it takes a long time, and the operation is more complicated. In order to get concrete resistance to chloride ion penetration in a relatively short period of time, the electro accelerated migration method was proposed and widely used.Non electric field, diffusion of chloride ion in saturated cement-based materials, and cement based materials, some of the hydration products and unhydrated cement mineral will interact with chloride ion by physical adsorption and chemical binding, so as to reduce the free chloride ion concentration in the pore solution, and delay of chloride ion penetration time of reaching to the surface of the steel bar. When applied voltage, due to electric field force, often electromigration coefficient is larger than the natural diffusion coefficient.The influence of applied voltage on matrix of chloride ion adsorption and chemical binding capacity and on the microstructure of matrix, the conclusion of different researchers is not consistent. Electro accelerated chloride migration test on chloride migration coefficient is calculated by assuming that the chloride concentration of the color changing boundary is 0.07mol/L. In the case of alkali activated cement, the composition of cementitious material, water glass module and the Na2 Ocontenthas a great influence on the hydration products and pore solution chemical composition, when using the accelerated chloride migration formula to calculate the migration coefficient, the color change boundary concentration of chloride ion is whether equally 0.07mol/l. At present, there is no literature on this research.The specimens after natural immersion test and electro accelerated migration test to steady state,the chloride condensation, total content of chloride ion and chloride ion binding capacity and on the microstructure of matrix were comparative study. A preliminary study on the concentration of chloride ions in the color changing boundary of the alkali activated cement materials after the electro accelerated migration was carried out.The concentration of chloride of specimens after natural immersion and accelerate the migration to steady-state was studied by using filter method. The results show that after applied voltage, free chloride ion concentration of pore solution of matrix was significantly higher than that of natural immersion. When the external solution of sodium chloride concentration was low, the influence of the voltage was more obvious. The slag and silica fume content had no significant effect on the ratio between natural immersion and migration, along with the increase of the amount of fly ash, the chloride condensation showed a downward trend.In this study, the content of total chloride ion and chemical binding chloride ion in the samples were studied. The results show that, compared with the natural immersion, the content of total chloride ion in the pastewas obviously increased. The lower the concentration of Na Cl, the more obvious the difference between the natural immersion and migration was. When applied voltage, the paste had no significant effect on the production of Friedel‘s salt. The formation of s’ Friedel salt in pure silica cement paste had nothing to do with natural soaking time, but was related to the content of total chloride ion in paste.The effect of applied voltage on the Zeta potential and microstructure of pure silicon cement paste was studied. The results show that, compared to the natural immersion, the applied voltage increased the Zeta potential value of the hardened paste, and as the concentration of Na Cl solution increases, the smaller the gap between natural immersion and migration,. The applied voltage can reduce the content of Ca(OH)2 in the matrix, and the ratio of calcium silicon of C-S-H increased, pore structure can be improved to a certain extent.The effects of different water glass modules, fly ash content and alkali content on the chloride concentration in the color changing boundary of the alkali activated cement were studied. When the water glass modulus was greater than 1, the chloride ion concentration of the alkali activated slag / fly ash mortar was significantly greater than that of the pure silica cement mortar. The concentration of chloride ion in the color changing boundary gradually decreased with the increase of the content of fly ash, and it had a better linear correlation, and it also decreased with the increase of the alkali content.The conversion of water soluble chloride ion concentration in color changingboundary to free chloride ion concentration ofthe alkali activated mortar was usd the formula of C_w=1.554C_f+0.3137(R~2=0.968), and was within the confines of the free chloride ion concentration range in Portland cement system. The method can be directly applied to the alkali activated cement system. But other conversion formulas and curing methods are whether still applicable, which need more systematic study.