Research On Rssistance Erosion Properties And Mechanism Of TSA Towards Cement-based Materials

The thaumasite form of sulfate attack is a special form of sulfate attackexists to thaumasite as degeneration products, it occurd in cement-based materi-al when exposed to the lower temperature, sulfates, carbonates and excess ofwater environmental conditions. Compared with the type of traditional sulfateattack, when the thaumasite form of sulfate attack to cement-based materials,there was no obvious swelling,cracking, but directly make C-S-H gel disintegratewhich is in cement paste, and cause a transformation of cement into a mushwhich has no strength, non-binding ability.Its distruction and concealment leadssignificant risks to concrete structures.This paper relies on the National Natural Science Foundation of China (51178363), in5℃low temperature environment, studys the content of limestonepowder, mineral admixture, curing system, the impact of environmental conditions and admixtures on TSA of cement-based materials. Erosion products wereby testing methods of X-ray diffraction analysis and Fourier transform infraredspectroscopy, to explore anti-corrosion properties and mechanism of TSA. Theresults show that:①The extent of degeneration increased with an increase in limestone amount. the surface of specimen without limestone has a slight peeling,flaking part,the performance of conventional sulfate attack. As limestone powder content is15%and30%, degeneration product showed thaumasite,and the product is mai-nly thaumasite, when the content of limestone is30%.②Slag, silica fume and fly ash can improve the anti-corrosion propertiesof cement-based materials, The effectivesness is closely related to content; Met-akaolin has aluminous phase composition, so it can make TSA more serious.Under the same conditions, the ability of anti-corrosion in descending order asfollows:60%SL>7.5%SF>30%SL>15%SF>30%FA>15%FA>blank>7.5%MK>15%MK. The effectiveness of mixed added of mineral admixture is better than thecorresponding single doped admixture.③Different levels of ash with same content, because the difference of co-mposition and fineness,it exhibit different anti-corrosion properties of cement-based materials. Fly ash with higher content of silica and alumina,and lower ign-ition loss performed positive effect. ④Different silicon content of silica fume, because of its excellent filling effect, ash effect and dispersion effects etc, can obviously improve the anti-corrosion properties of mortar specimens. With the increment of silica fume silica content,the role of anti-corrosion of cement-based materials was improved with an increase in amount the role of anti-corrosion properties in turn increases, which Elekm improve optimal effect.⑤In different pre-curing systems,the degree of tsa erosion and the mortarsuffered more degradation in air curing,standard curing and isolated form the air conditions, in ascending order.When pre-air curing, the resulting calcium carbonate-filled pores,improve the density of the specimen, to prevent ions form the outside inwards and improved the ability of anti-tsa erosion;while isol-ated from the air, the lack of outside water supply,hydration is not complete,increased the porosity of erosion and damage facilitated.⑥Compared with the same concentration of sodium and calcium sulfate,the damage of specimen increased in magnesium sodium is more serious; Ma-gnesium sulfate etchant, the concentration of5%severely damaged, While5%sodium and5%calcium sulfate destructive erosion of the specimen at5%mag-nesium sulfate.⑦The early strength agent of triethanolamine and sodium chloride can e-nhance the capacity of early resistance to low temperature sulfate attack,but th-eerosion of the late improvement effect gradually weakened,and because the sol-ubility of sodium chloride to gypsum, it has poor results to pre improving. Sodium gluconate slowed the degree of cement hydration,reducing structural dens-ity,accelerated erosion occurs.