Modification And Mechanism Of Cement-based Materials By Cellulose Ether And Latex Powder

Cement-based materials,as brittle materials,have poor flexibility,easy shrinkage cracking,low tensile strength and other problems,which tend to become the short board of the structure when applied to construction engineering.In addition,with the increasingly stringent requirements on the fluidity,cohesiveness,water retention and setting time of cementitious materials in the construction process,cementitious materials are gradually exposed to be inadequate.Based on these two aspects,how to improve the working performance and toughness of cementitious materials has become an urgent problem to be solved.Three types of cellulose ethers and four types of latex powders were selected to study the rheological properties of cement slurry,and to summarize the action patterns of polymers on plastic viscosity and yield stress of cement slurry when acting individually and in combination.The influence of polymers on macroscopic properties such as fluidity,flexural and compressive strength,flexibility of mortar were studied.The mechanism of polymer modification on cementitious materials was investigated by microscopic tests such as heat of hydration,zeta potential,total organic carbon content,X-ray diffraction and thermogravimetry.It was found that cellulose ether can significantly improve the yield stress and plastic viscosity of cement slurry,and it is related to the dosage of cellulose ether and its viscosity.The dosage is an important factor affecting the fluidity of the cement mortar,and the HPMC-4dosage of 0.5%was found to be the same as the base mortar fluidity.Cellulose ether has a negative effect on the flexural and compressive strength of mortar,and the toughness of mortar can be improved by about 69%.Cellulose ether complexed with Ca²⁺at the early stage of hydration,which significantly delayed the hydration process,extended the time up to 5.1h,and reduced the content of hydration products up to 49%.Cellulose ether can adsorb water molecules in the early stage of cement hydration to achieve a retarding effect,then gradually released to play a role in water retention,with a good effect in the 4h-12h of cement hydration.Latex powder can reduce the yield stress and plastic viscosity of cement slurry.When VAE-1 dosage was 8%,the yield stress and plastic viscosity of slurry decreased by 13%and42%.Latex powder significantly improves the fluidity of mortar by up to 54%.Latex powder can improve the flexibility of mortar,and the flexibility increases with the increase of dosage.Latex powder releases carboxyl groups at the initial stage of hydration,reacts with Ca²⁺to generate water molecules and calcium formate,delaying the hydration process of cement,but it has no obvious delaying effect of cellulose ether.After emulsion powder was added,8h chemical binding water content increased.With the increase of latex powder content,Ca（OH）₂decreased more obviously,up to 26.0%,and the inhibition of hydration process increased with the increase of latex powder content.The combined effect of cellulose ethers and latex powder is a superposition of their individual effects.The effect of changing the type of cellulose ether on the yield stress and plastic viscosity remains the same:HPMC-20>HPMC-4>HEMC-4.The rheological parameters decrease with the increase content of latex powder.Compared with latex powder,the change of cellulose ether content has a greater influence on the flexibility of mortar.The influence of the combination of the two on cement hydration process is greater than that of the single effect,and the longest delay can be 6.7h.The delay effect of cellulose ether on the hydration of the cement is stronger than latex powder.Although the hydration product production can be reduced by changing the dosage and type of latex powder,the effect is weaker than that of cellulose ether.Cellulose ether affects the hydration reaction through adsorption and hydration.Latex powder affects the hydration reaction through dispersion,film formation and chemical action.Cellulose ether and latex powder in the presence of competitive adsorption,latex powder will be adsorbed on the surface of cellulose ether molecules,resulting in interference.