Effect Of Polymer Viscosity Enhangced Agent On Properties Of Fresh Cement Paste And Mechanism Research

High fluidity and high stability concrete mixture is the main feature of high-performance concrete.Because high fluidity concrete is easy to separate and bleed,polymer viscosity enhangced agent is often used to solve the problem of concrete workability.Xanthan gum and Welan gum are green,environment-friendly and renewable polysaccharide biological gum viscosity enhangced agents,which are more and more used in cement-based materials.However,at present,there is little research on the action mechanism of polymer viscosity enhangced agent on cement paste and its effect on cement hydration,which needs to be improved.In this paper,the effects of Xanthan gum,Welan gum and three kinds of hydroxypropyl cellulose ether HPMC with different molecular weight on the workability and rheological properties of fresh cement paste and their mechanisms are studied.The fluidity of fresh cement paste mixed with high molecular viscosity enhangced agent is tested.It is found that the order of five kinds of high molecular thickening effects is:Welan gum>Xanthan gum>15W HPMC>10W HPMC>3W HPMC.Under the condition of W/C=0.5,the optimal dosage range of five kinds of high molecular viscosity enhangced agents is:Xanthan gum≤0.15%,Welan gum≤0.15%,3W HPMC≤0.2%,10W HPMC≤0.2%,15W HPMC≤0.15%;After the test of bleeding rate,it is found that the order of anti bleeding segregation ability is 15W HPMC>10W HPMC>3W HPMC>Welan gum>Xanthan gum.In order to ensure that the bleeding rate of fresh cement paste reaches 0%when W/C=0.5 at60min,the content of each high molecular viscosity enhangced agent is:Xanthan Gum 0.2%,Welan gum 0.2%,3W HPMC 0.15%,10W HPMC 0.15%,15W HPMC 0.1%;After the setting time test,it was found that the retarding ability of the five polymer viscosity enhangced agents was ranked as HPMC>Welan gum>Xanthan gum,and the correlation between the retarding ability of HPMC and molecular weight was low.After testing the rheological properties of fresh cement paste,it is found that the higher the yield stress and plastic viscosity,the lower the fluidity of cement paste.Compared with fresh cement paste without polymer viscosity enhangced agent,the yield stress,plastic viscosity and thixotropy of fresh cement paste with polymer viscosity enhangced agent are increased;The yield stress,plastic viscosity and thixotropy of fresh cement paste increase gradually with the increase of polymer viscosity enhangced agent content,cement hydration time and HPMC molecular weight;Compared with HPMC,fresh cement paste mixed with Xanthan gum and Welan gum is more suitable for low or high temperature construction environment;The fresh cement paste mixed with warm wheel glue is less affected by water cement ratio;The order of yield stress,plastic viscosity and thixotropy of fresh cement paste improved by five polymer viscosity enhangced agents is as follows:Welan gum>Xanthan gum>15W HPMC>10W HPMC>3W HPMC.DLVO theory is used to analyze the total potential energy between cement particles in the fresh cement paste.It is found that HPMC will reduce the potential barrier height of the fresh cement paste.Compared with the fresh cement,the fresh cement paste mixed with HPMC is more prone to aggregation and sedimentation.With the increase of HPMC molecular weight,the potential barrier height gradually decreases and the flocculation ability gradually increases.With cement hydration,cement particles gather together to form aggregates,the agglomerates in the fresh cement paste were observed by using the ultra depth of field microscope,and the agglomerates were quantitatively characterized by using the fractal dimension.It was found that the polymer viscosity enhangced agent would increase the fractal dimension of the agglomerates,increase the size of the agglomerates and reduce the fluidity of the fresh cement paste.The order of fractal dimension of fresh cement paste mixed with polymer viscosity enhangced agent:Welan gum>Xanthan gum>15W HPMC>10W HPMC>3W HPMC.Through TOC test,it is found that compared with HPMC,the adsorption capacity of Xanthan gum and Welan gum on the surface of cement particles is greater,and the adsorption capacity of Welan gum is the largest;Through Zeta potential test and ion concentration test of K⁺and Na⁺in paste body fluid phase,it is found that there are more negative ion groups（Hydroxyl and Carboxyl groups）in the side chains of Xanthan gum and Welan gum.The concentration of Ca²⁺and SO₄^2-ions was measured.It was found that the concentration of Ca²⁺and SO₄^2-ions in the fresh cement paste mixed with HPMC decreased the most,which decreased by 44.8%and 48.6%respectively compared with the blank group,it has the strongest retarding ability to cement hydration process;Through hydration heat,XRD and thermogravimetric tests,it is found that polymer viscosity enhangced agent will not increase the types of hydration products,but will delay the hydration induction period of fresh cement paste.