Effect Of Chemical Admixtures With Different Functional Groups On Cement Hydration And The Mechanisms

Cement hydration is one important process to change cementitious materials from loose powders to hardened cement stone.Any effect on cement hydration will certainly affect the properties of cementitious materials.Besides,organic chemical admixture is one indispensable ingredient in the modern concrete industry to conquer the drawbacks of cementitious materials.However,the addition of chemical admixtures into cementitious materials also has great effect on cement hydration,which will surely lead to the change of final macroproperties.Hence it is very important to understand the different effect caused by the addition of different organic chemical admixtures.The effect of chemical admixtures on cement hydration is closely relevant to the interaction between organic admixtures and cement grains,which is directly decided by the functional group in the molecule of organic admixtures.From this aspect,this thesis focuses on the effect of organic chemical admixtures with different functional groups on cement hydration.Besides,we mainly talk about three kinds of organic chemical admixtures,namely organic molecules,water soluble polymers and polymer dispersion.The effect of these admixtures on cement hydration and the mechanism behind were discussed through the combination of calorimetry test,in-situ XRD,adsorption measurement,pore solution analysis and confocal observation and so forth.To the organic molecules,it is found that the molecules with different functional groups and different molecular structures show various retardation effect on cement hydration.Molecules with phosphate group significantly retard the cement hydration.Besides,the molecules with same functional group but different molecular structure also show different effect on cement hydration.The addition of hydramine will accelerate the aluminate reaction but retard the silicate reaction,which leads to the different effect on the setting of cementitious materials along with the increasing dosage.Besides,the triethanolamine shows stronger ability than diethanolisopropanolamine.To the water soluble polymers with carboxy group,firstly they show significantly stronger ability to retard cement hydration compared to the organic molecule with the same functional groups and same mole addition of these groups.The complexation of carboxy group in the polymer with the free calcium ion in solution is not the essential reason to the retardation effect on cement hydration.Besides,water soluble polymer will be adsorbed on the surface of cement grains,the adsorption of polymer on the surface of cement grains will significantly prevents the nucleation and growth of the hydration products,which explains their retardation effect on cement hydration.To the polymer dispersion,the effect of polymer with four different functional groups was compared and discussed with the combination of in-situ XRD and pore solution analysis.It is found that the polymer with positive charge on surface show less retardation effect on cement hydration compared to the other three polymers.The addition of polymer will obviously retard the nucleation and growth of C-S-H,but polymers with carboxy and sulfonic groups show stronger ability compared to polymer with positive surface.C-S-H will be formed on the surface of polymer by the first complexation of carboxy group with calcium ion and then the reaction of calcium ion with silicate ion in solution,which changes the polymer particles as new nucleation site for C-S-H.It provides a new direction for the development of inorganic and organic cementitious materials.The effect of complexation on cement hydration was further developed.The addition of polymer into cement paste will change the ion distribution in the pore solution through complexation,which will affect the nucleation process and then retard the cement hydration.Based on the investigation above,the obstacles faced in the application of styrene acrylate(SA)polymer were discussed and the effective methods to solve these problems were proposed.The super-retardation effect of SA polymer on cement hydration under high temperature is caused by the continuous hydrolysis of acrylate in the alkaline condition and the incorporation of TPEG on their surface of polymer particles can decrease the adsorption of SA polymer on the surface of cement grains and then mitigate the super-retardation effect.Finally the polymers with different functional groups on the rheological property of cement paste were discussed.