Effect Of Expansion Agent On Rheology And Hydration Characteristics Of Cement-PCE Slurry

Adding an appropriate amount of expansion agent to make shrinkage-compensating concrete is one of the most common technical measures to control concrete cracking.Superplasticizer is an indispensable chemical admixture for commercial concrete.With the development of high performance concrete and other advanced cement-based composite materials,the shrinkage-compensating concrete prepared by adding an appropriate amount of high performance superplasticizer can achieve good workability,uniformity and compactness.At present,there are few researches on the effect of compensating shrinkage cementing material system on high-performance superplasticizer in the theory of expansion agent and superplasticizer,the microscopic mechanism is not systematic,and the theoretical lags is behind the engineering application.In this paper,the effects of different types and dosage of expansion agents on rheological properties,hydration properties,mechanical properties and expansion properties of cement-PCE slurry are studied.The main conclusions are as follows:（1）The fluidity of cement-PCE slurry increases with the increase of PCE dosage,but the increase range first increases and then decreases.The influence of expansion agent on the fluidity of cement-PCE slurry is different from the mortar system.For the net slurry system,both expansion agent and cement-PCE slurry have little influence on the fluidity of cementPCE slurry.For the mortar system,the two expansion agents have a great influence on the fluidity of mortar,and the greater the dosage of expansion agent,the greater the degree of fluidity reduction.Compared with the two expansion agents,the loss of slurry fluidity caused by calcium sulfoalumate-calcium oxide expansion agent（AC）is greater than that of calcium sulfoaluminate expansion agent（A）.It can be considered that rheological parameters can better characterize the influence of expansion agent on slurry fluidity.（2）After adding expansion agent,the PCE adsorption amount decreases with the increase of expansion agent dosage,and increases first and then decreases with time,which is consistent with the change law of slurry fluidity,which can well explain the microscopic mechanism of the influence of expansion agent on the rheological properties of cement-PCE slurry.The variation of Zeta potential and conductivity with the amount of expansion agent is inconsistent with that of rheological properties.The possible reason is that although Zeta potential is an important factor affecting the dispersion of cement slurry,it is not the only one,so the rheological properties of cement-PCE slurry cannot be fully and fully explained..（3）Adding expansion agent can shorten the time of cement hydration induction period and advance the appearance of the second heat release peak.PCE can reduce the hydration heat release and hydration heat release rate of cement slurry,and the law that the higher the content of PCE,the greater the corresponding decrease of hydration heat release and hydration heat release rate of cement slurry.The two kinds of expansion agent can promote the hydration of cement,with the increase of expansion agent dosage,the promotion degree increases;The promoting effect of expansion agent on slurry hydration process will be weakened by the retarding effect of PCE,although the retarding effect is further amplified with the increase of PCE content,but it will not cover the promoting effect of expansion agent on cement hydration.（4）Adding expansion agent can reduce the compressive and flexural strength of hardened slurry,and the strength reduction degree increases with the increase of expansion agent content.Compared with the reference group,the strength reduction degree of group A is greater than that of group AC.