| Chloride erosion is the largest contributor to the corrosion of the steel in concrete. Therefore it is important to reduce the damage of chloride ion on the steel to improve the durability of reinforced concrete structures. In this thesis, pH value, chloride ion concentration and [Cl-]/[OH-] of the simulated concrete pore solutions before and after calcium silicate hydrates (one of the main Portland cement hydration products) treatment were investigated. And the corrosion behavior of steel samples in pore solutions treated with calcium silicate hydrates was investigated through corrosion potential monitoring, polarization curves, electrochemical impedance spectroscopy and full-immersion weight-loss experiment. Surface morphology of the steel in pore solutions treated with and without calcium silicate hydrate treatment was studied by optical microscope and scanning electron microscope (SEM). And by means of X-ray photoelectron spectroscopy (XPS), surface compositions of the steel in pore solutions before and after calcium silicate hydrate treatment were analyzed. X-Ray Diffraction (XRD) was used to study the structure of the calcium silicate hydrate. The main conclusions are as follows:(1) Calcium silicate hydrate could effectively adsorb chloride ions and decrease the chloride content in different pH values (pH:12.5,11.9,10,9.7 and 9.3) simulated concrete pore solutions. But the pH values various of these pore solutions were different after calcium silicate hydrate treatment. For Group A pore solutions (pH=12.5 and 11.9), the pH values decreased after 3% calcium silicate hydrate treatment, which can be explained by the reactions between acidic silanol Si-OH in calcium silicate hydrate structure and OH- in the pore solutions. While for Group B pore solutions (pH=10,9.7 and 9.3), after 3% calcium silicate hydrate treatment the pH values increased. It may be due to the strengthening of CO32- and HCO3- hydrolysis and the inhibition of HCO3- ionization by calcium silicate hydrate.(2) After 3% calcium silicate hydrate treatment, for Group A pore solutions (pH=12.5 and 11.9), both the diameter of the semicircle and polarization resistance Rp of the steel reduced, passivation was more difficult, and the steel corrosion was improved through optical microscope and SEM. While for Group B pore solutions (pH=10,9.7 and 9.3), the Epit diameter of the semicircle and Rp of steel in the solutions increased, the corrosion susceptibility decreased, and the steel corrosion decreased through optical microscope and SEM.(3) Several groups of pore solutions with different components were made. The pH value of pore solutions were 12.5 and 9.7 respectively Calcium silicate hydrate promoted the corrosion of the steel in three groups of pH=12.5 pore solutions with different components, while inhibit the corrosion of the steel in three groups of pH=9.7 pore solutions with different components. The experimental results showed that the effects of calcium silicate hydrate mainly depended on pore solutions pH value, but not on the components of the pore solutions.(4) With the calcium silicate hydrate content increasing (1%,3%,6%), corrosion rate of the steel in pH=12.5 pore solutions increased. The reduction extent of corrosion rate of the steel in pH=9.7 pore solutions increased firstly and then decreased. The corrosion rate of steel was minimum when calcium silicate hydrate content was 3%.(5) In the certain range of temperature (0-60℃), the possibility of the steel corrosion increased in pore solutions (pH=12.5) whether it was treated by calcium silicate hydrate or not. It is because that the process of electrochemical corrosion of steel, the rate of anodic reactions and cathode reactions increased as the temperature increased. The promoting effect on steel corrosion by calcium silicate hydrate reduced, as the temperature increased (0℃,30℃and 60℃). |
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