The Adsorption Characteristics Of Anti-Sulfate Corrosion Agent And Influence On The Performance Of Cement Concrete

Sulfate corrosion is the reaction between sulfate ions and cement hydration products,which causes concrete expansion,cracking and spalling.Sulfate corrosion damage is one of the key factors affecting the durability of concrete materials.How to improve the sulfate corrosion resistance of concrete materials is a hot topic today.The common method is to optimize the cement composition,such as reducing the content of C₃A,and add mineral admixtures,such as blast furnace slag,fly ash,volcanic ash,etc.Although reducing the content of C₃A can effectively prevent the secondary crystallization of ettringite,it has no effect on the precipitation of gypsum and thaumasite,and the expansion of gypsum and the formation of thaumasite are important factors causing the expansion and cracking of concrete.Layered double hydroxides（LDHs）,as hydrotalcite,can replace sulfate ions and interlayer anions in cement-based materials due to their special two-dimensional layered structure and exchangeable interlayer anions,thereby improving the sulfate corrosion resistance of cement-based materials.In this paper,barium carbonate was found in the process of synthesizing Mg-Al hydrotalcite by co-precipitation method.Through the adsorption experiment of sulfate ion,it was found that both of them had strong sulfate ion adsorption capacity.Mg-Al hydrotalcite and barium carbonate were used as the research objects to study the effects of temperature,p H,dosage and other factors on the adsorption of sulfate ions.With the help of adsorption kinetic model and adsorption thermodynamic model,the adsorption characteristics of two sulfate corrosion inhibitors were explored.Two kinds of anti-sulfate corrosion agents with different contents were added to cement paste and cement mortar to study their effects on the fluidity of cement and and strength of cement mortar.At the same time,the effects of two anti-sulfate corrosion agents on the corrosion resistance of cement mortar were investigated by long-term sulfate immersion test,sulfate dry-wet cycle test and simulated seawater tide test.Two kinds of anti-sulfate corrosion agents with different contents were added to concrete to explore their effects on the working performance,strength performance,sulfate corrosion resistance and shrinkage performance of concrete.The following conclusions are obtained.（1）The ability of barium carbonate to adsorb sulfate ions in water is better than that of Mg-Al hydrotalcite.The adsorption of sulfate ions by Mg-Al hydrotalcite and barium carbonate conforms to the pseudo-second-order kinetic model.Barium carbonate conforms to the Freundlich adsorption isotherm model,and Mg-Al hydrotalcite conforms to the Langermuir adsorption isotherm model.It is speculated that the adsorption of sulfate ions by Mg-Al hydrotalcite is mainly due to physical adsorption,and the electrostatic attraction between molecules will also affect the adsorption of sulfate ions.The physical adsorption of sulfate ions by barium carbonate plays a role,and chemical reactions also occur.（2）The fluidity of cement paste increases with the increase of barium carbonate content.But with the Mg-Al hydrotalcite.The fluidity of cement paste decreases obviously with the increase of stone content.The addition of barium carbonate has little effect on the compressive strength and flexural strength of cement mortar.The addition of Mg-Al hydrotalcite reduces the compressive strength and flexural strength of cement mortar.When the content of barium carbonate and Mg-Al hydrotalcite is not more than 4%,it can improve the ability of cement mortar to resist simulated seawater corrosion,corrosion resistance to different immersion states of sulfate,frost resistance and salt frost resistance and resistance to sulfate dry-wet cycle.（3）When the content is not more than 3%,barium carbonate has little effect on the fluidity and compressive strength of concrete,while Mg-Al hydrotalcite significantly reduces the fluidity and compressive strength of concrete.Barium carbonate and Mg-Al hydrotalcite are beneficial to reduce the shrinkage of concrete,have little effect on freeze-thaw resistance,and can enhance the sulfate corrosion resistance of concrete.