The Effect Of Adjustable Solidification Agent On Cement Hydration Induction Period

In the concrete material,in addition to cement,sand,stone,and water,the chemical admixtures have become the indispensable fifth components,playing an increasingly important role in modern cement concrete.It is often necessary to add chemical admixtures to adjust the hydration rate of cement,which mainly includes retarder and accelerator.At present,the researches of domestic and foreign scholars mainly focus on cement setting time,cement hydration process and mechanism when adding retarder or accelerator alone.Although the combination of retarder and accelerator can lead to increased flexibility in controlling cement hydration and setting time,there are few researches published.In this paper,the effects of sucrose?Suc?,sodium gluconate?SG?,and amino trimethylene phosphonic acid?ATMP?on corresponding hydration process of cement and regulation mechanism were discussed.Then accelerator such as calcium hydroxide?CH?,aluminum sulfate?AS?and calcium nitrate?CN?were added to the retarded cement paste,and the suppression mechanism of accelerator on the retarding effect of the three retarders were discussed.In this research we established a“retarder-accelerator”system,which can delay the setting time of cement and break down the retarding mechanism according to the actual needs of the project,so as to realize the control of cement hydration and setting time.The results showed that:sucrose can inhibit the hydration of C₃S but promote the early hydration of C₃A,accelerating the formation of AFt,and there effects are stronger with the increasing of sucrose increases;Due to adsorption and complexation,sodium gluconate can accelerate the dissolution of C₃A in the early hydration of cement,and inhibit the hydration of C₃S and the formation of CH,which can effectively reduce the heat of hydration and retard the hydration of cement;ATMP is a kind of organic phosphonic acid salt,and can rapidly form micro soluble chelates with Ca²⁺in cement paste,wrapping on the surface of cement particles and retarding the hydration process of cement.CN can provide crystal nucleation for cement hydration products and accelerate the crystallization of hydration products,shorten the induction period of sucrose-retarded cement.For sodium gluconate and ATMP which play the role of retardation mainly through the complex,aluminum AS can capture the complexed Ca²⁺and broke the complex film coating on the surface of cement particles;Also needle-like ettringite is connected to form a network structure,shortening the induction period of retarded cementIn the cement paste,“0.1%Suc-2%CN”,“0.1%SG-3%AS”,“0.1%ATMP-3%AS”as“retarder-accelerator”system can first delay the hydration of cement,and then promote the hydration of retarded cement,realizing the control of cement hydration and setting time.