Study On The Law Of Binding Chloride Ion Of C₄AF Mineral

With the increasing strategic position of marine development,marine engineering construction has ushered in a new period of development,and the use of offshore concrete has grown significantly.However,concrete in the current offshore environment is subject to serious chloride ion attack and faces serious challenges in durability.Therefore,This paper systematically investigates the pattern of binding chloride ions by C₄AF minerals in silicate cement.1.The effect of gypsum on the performance of C₄AF hydrated paste binding chloride ions was investigated.The hydration product of C₄AF,hydrargyrite（C₃（A,F）H₆）,was found to react directly with chloride salts to form Friedel’s salt,which has a strong ability to bind chloride ions.When mixed with gypsum,C₄AF and gypsum undergo hydration reaction to produce monosulfur type hydrated calcium aluminosulfate（AFm）,and with the increase of gypsum dosing,the amount of AFm generation gradually increases.After erosioned by chloride ions,the chloride ions replace the sulfate ions in AFm to generate Friedel’s salt,and the amount of Friedel’s salt generated gradually decreases with the increase of gypsum admixture.The chloride ion cannot completely replace the sulfate ion in AFm,and the ability of AFm to bind chloride ion by replacement reaction is weaker than the ability of C₃（A,F）H₆to react directly with the chloride salt to form Friedel’s salt.2.The effect of magnesium doping on the properties of C₄AF hydrated paste and its binding chloride ions was investigated.Magnesium is found to be mainly solidly soluble in the calcium and iron sites in C₄AF minerals,the solid solubility is less than2%,and excess magnesium exists as free magnesium oxide.Magnesium doping can enhance the ability of C₄AF hydration paste to bind chloride ions,with the increase of magnesium doping,C₄AF hydration paste binding chloride ions more and more.Magnesium doping promotes the firing of C₄AF,and the hydration product C₃（A,F）H₆production increases,and Friedel’s salt production increases.Only the Mg solidly solved at the Ca site is involved in the conversion of C₃（A,F）H₆binding chloride ions to Friedel’s salt.The hydration of magnesium in the form of free magnesium oxide produced Mg₄Al₂（OH）₁₄·3H₂O,whose laminar structure with a large internal specific surface area helped to adsorb more chloride ions and promoted the formation of Friedel’s salt.3.The effect of C₄AF content on the chloride properties of cement paste binding was investigated.The ability of cement paste to bind chloride ions was found to be enhanced when C₄AF content was increased.At 23.59%C₄AF content,the cement hydration paste has the strongest ability to chemically binding chloride ions,The highest compressive strength of cement specimens was achieved at 20.11%C₄AF content.Considering the amount of binding chloride ion and the mechanical properties of cement,the best content of C₄AF is 16%.