Study On Application Performance Of Sulphoaluminate-based Strength-promoting And Shrinkage-reducing Admixture

The incorporation of a certain amount of expansion agent in the concrete can compensate for the shrinkage of the concrete,improving the anti-seepage and cracking resistance of the concrete.However,there are some problems in the use of the expansion agent,such as the problem of temperature rise in mass concrete,the durability of the expansive concrete.So it is very necessary to develop new expansion agent.In this paper,a new type of expansion agent—sulphoaluminate-based strength-promoting and shrinkage-reducing admixture?SP-SRA?that can improve the early and late strength of cement concrete,reduce the drying shrinkage of cement concrete,and improve the anti-shrinkage and impermeability of cement concrete was incorporated into cement concrete.Firstly,the effects of different dosage of SP-SRA on the mechanical strength and macroscopic properties of cement mortar were studied.Second,The effects of sulfur on the formation of delayed ettringite in SP-SRA were studied.The effects of sulfur on the mechanical properties of mortar and the expansion rate were analyzed by XRD,SEM and other micro-methods.And finally the effects of SP-SRA on the durability of concrete were studied.The results show that:?1?The addition of SP-SRA promotes the hydration rate of cement in the early stage.With the increase of SP-SRA content,the compressive strength of cement increases gradually,and the dry shrinkage decreases significantly.The content of ettringite about 3d and 28d gradually increased,and the content of Ca?OH?₂ decreased gradually.With the progress of hydration,the micropores of cement slurry mixed with SP-SRA gradually increased,while the macropores gradually reduced.The product of the hydration reaction is filled with cement pores,making the cement stone more compact.?2?The cement with SP-SRA will not form the delayed ettringite at standard curing,However,when the early steam curing temperature reached 90?,and experienced two wet and dry cycle,the specimen that SP-SRA-standard cement system and sulphoaluminate cement+hard gypsum+standard cement system produced micro-cracks at the age of 28d.There are a large number of needle-like ettringite at the age of 56d by SEM.There are some guess about the formation of delayed ettringite:After 90?curing,a large number of ettringite transform into a single sulfur-type hydrated calcium sulphoaluminate,and then in the normal wet conditions,the ettringite is regenerated in the ion-enriched region.The Al ions and S ions are precipitated on the nuclei through the solution transporting.The crystals grows up continuously at the microcracks.At the same time,due to lack of space,ettringite change into needle-shaped,resulting in the expansion of the specimen.?3?Compared with the Portland cement concrete,concrete with SP-SRA has a better workability and better mechanics'performance,and the majority of durable indexes also surpass that of the Portland cement concrete.