Synthesis Of Mesoporous Silicas And Their Adsorption Properties For Chloride Ions In Cement Paste

Due to the insufficient durability of concrete structures,it is common for serious accidents to occur before the designed life is reached.Chloride ion erosion is the main cause of durability damage of concrete structures.to improve the ability of chloride ion erosion resistance of concrete structure is of great practical significance to improve the durability of concrete.It is one of the traditional methods to increase the resistance of concrete to chloride ion erosion by adding mineral reference materials.Most of the mineral reference materials only delay the transmission of chloride ions in concrete.There is a large space for the study of new functional materials from the perspective of chemical adsorption of chloride ions.Mesoporous silica,as a new type of inorganic functional material,has the characteristics of ultra-high specific surface area,large pore volume,controllable morphology and size,and has been widely used in the field of chemical adsorption.However,there is still no research on the adsorption of chlorine ions in cement slurry.In order to explore the materials with excellent properties of curing chloride ions in cement base,this paper studied the properties of mesoporous silica materials in curing chloride ions in cement slurry.In this paper,a series of mesoporous silica materials with different pore sizes were synthesized by hydrothermal method,and their structures were characterized.The adsorption performance of mesoporous silica on chloride ions in aqueous solution was studied,and the materials with the best adsorption effect were selected.The effects of temperature,concentration of adsorbent,concentration of chlorine ion and pH value on the adsorption capacity of chlorine ion were studied.The adsorption kinetics and adsorption thermodynamics of the adsorption process were analyzed.The curing ability of mesoporous silica in cement paste and cement mortar at different ages and chloride ion concentrations was studied.main research results include:(1)three kinds of mesoporous silica materials SBA-15,MCM-41and KIT-6 were successfully synthesized by hydrothermal method.The characterization results showed that MCM-41 had more smaller mesopores,more irregular pore structure and larger specific surface area than SBA-15 and KIT-6,reaching 1036 m~2/g.(2)At 30℃,pH of 6 cases,MCM-41,SBA-15 and KIT-6 reach adsorption equilibrium after 2h,the adsorption ability of chloride ion in the water,MCM-41 significantly higher than the other two;MCM-41 of chloride ions in the water adsorption of the optimal process condition is:temperature of 55℃,pH value of 6,adsorption time is 2h,Cl~-concentration of 584 mg/L,adsorbent concentration is 1.0 g/L,maximum time is 188.18 mg/g;The adsorption kinetics of chlorine ion by MCM-41accords with the quasi-second-order kinetic equation and belongs to the composite adsorption process.The adsorption isotherm was more consistent with Langmuir equation.(3)The adsorption performance of MCM-41 on chloride ion is the best in aqueous solution.The adsorption effect in cement slurry is slightly lower than that in water,and the adsorption effect in cement mortar is slightly lower than that in water.The higher the curing age,the higher the curing amount of chloride ion in MCM-41 cement slurry(net slurry,mortar).With the increase of chloride ion concentration in cement slurry(net slurry,mortar),the adsorption amount of chloride ion by MCM-41increased correspondingly.