Sulfate Resistance And Mechanism Of Sulphoaluminate Cement Clinker-gypsum-limestone

With the proposal of national strategies such as“Maritime Power”,“Belt and Road”,“Western Development”,a large number of concrete infrastructure began to serve in harsh environments.Sulfate attack is one of the main reasons for the deterioration of concrete performance in service environments such as ocean and western salt lakes.The deterioration of concrete due to sulfate attack is very serious,and the service life is often difficult to meet the design requirements.How to improve the sulfate resistance of concrete and prolong the service life of structure is a major engineering problem to be solved.In this paper,according to the requirements of infrastructure construction for the long life of concrete materials,the sulfate corrosion resistance and mechanism of sulphoaluminate cement clinker-gypsum-limestone were studied.The main research contents and conclusions are as follows:（1）The hydration and hardening properties of sulphoaluminate cement clinker-gypsum binary system were studied,and the effects of gypsum content on the hydration rate,flexural/compressive strength,hydration products,microstructure and pore structure of sulphoaluminate cement were mainly explored.The results showed that the addition of gypsum increased the early hydration rate but decreased the 24 h total heat release.The hydration products of binary system are mainly AFt,AFm,AH₃ gel and C-S-H gel.The increase of gypsum content can increase the AFt content,reduce the porosity of mortar and improve the flexural/compressive strength of mortar.（2）The hydration and hardening properties of sulphoaluminate cement-gypsum-limestone ternary system were studied.Based on the flexural/compressive strength,mass change,relative dynamic elastic modulus,dimensional stability,hydration products and microstructure of slurry,the influence of limestone content on the properties of sulphoaluminate cement was analyzed.The results show that the incorporation of limestone reduces the 24 h cumulative heat release of slurry;the hydration products of the ternary system were mainly AFt,AFm,AH₃ gel and C-S-H gel,and the incorporation of limestone had no effect on the phase composition of the hydration products.The addition of limestone increases the porosity of hardened mortar,and the flexural/compressive strength of mortar decreases with the increase of limestone content.However,limestone can inhibit the flexural strength of sulfoaluminate cement from shrinking,and the more limestone content,the more obvious the effect.（3）The flexural/compressive strength,mass,relative dynamic elastic modulus,phase composition,microstructure evolution and dimensional stability of sulphoaluminate cement clinker-gypsum binary system under sulfate attack were studied by dry-wet cycle test method.The results show that the sulphoaluminate cement clinker-gypsum binary system has excellent sulfate resistance,and the mortar has good dimensional stability under sulfate action.The increase in gypsum content can improve the sulfate resistance of the system,and the best content is 15%;under the action of sulfate,the phase composition of binary system did not change,mainly AFt,AFm,AH₃gel and C-S-H gel.（4）The sulfate resistance of sulphoaluminate cement clinker-gypsum-limestone ternary system was studied by the same method as that of binary system.The results showed that the ternary system had good mechanical properties and dimensional stability under sulfate attack.The increase of limestone content can not only inhibit the decrease of slurry strength,but also delay the decrease of flexural strength,and the optimum content is 15%.Under the action of sulfate,the phase composition of ternary system has no obvious change,mainly AFt,AFm,AH₃ gel and C-S-H gel.（5）The flexural/compressive strength,mass,relative dynamic elastic modulus,phase composition,microstructure evolution and dimensional stability of sulphoaluminate cement clinker-gypsum-limestone ternary system eroded by sodium sulfate solution at different temperatures were studied by sulfate immersion test.The results showed that the ternary system had good sulfate resistance at different erosion temperatures.When the temperature is low,the compressive strength of the slurry has been increased,and the phase components are mainly AFt,AFm,AH₃ gel and C-S-H gel,but a small amount of Ca CO₃ will participate in the reaction.When the temperature is high,the mechanical properties of the slurry are poor,the compressive strength does not increase,and the phase composition is mainly AFt,AFm,AH₃ gel and C-S-H gel.