Research On Application Of Polymer In Dry-mixed Mortar

As one of the commonly used admixtures for modified dry-mixed mortar properties,polymers usually have a significant impact on the microstructure and corresponding macroscopic properties of mortars.The comparative study on the series of polymer admixtures containing different functional groups will help reveal the mechanism of action between the polymer and cement mortar and the corresponding structure-activity relationship,so as to provide a certain theoretical basis for the application of polymer in dry-mixed mortar.To this end,this article focused on the role of seven water-soluble polymers of polyvinyl alcohol,polyvinylpyrrolidone,sodium polyacrylate,polyacrylamide,hydroxypropyl methylcellulose ether,guar gum,and xanthan gum in dry-mixed mortar and a comparison was made.The influence and mechanism of polymer-modified dry-mix mortar were analyzed,and the influence of different functional groups on the microstructure and macroscopic properties of cement mortar was discussed by using various technical means such as XRD.According to the ratio of cement paste material,the polymer was mixed with the cement paste,and the hydration reaction was carried out for 7 days.The results shown that the incorporation of the seven polymers would not cause the hydration reaction to generate new products,but could make the crystal size of the hydrated product Ca(OH)₂smaller;and they all could inhibit the hydration process of the reactants tricalcium silicate(C₃S)and the reactants dicalcium silicate(C₂S);Sodium polyacrylate and xanthan gum containing-COO^-could inhibit the further conversion of Ca(OH)₂to Ca CO₃,and had a significant impact on the morphological growth of silica gel(C-S-H)and ettringite;polyacrylamide,guar gum,and sodium polyacrylate could effectively reduce the heat of hydration,and the reduction ratios were 7.82%,3.18%,and 1.42%,respectively.According to the ratio of cement mortar material,the polymer and cement mortar were mixed,the fluidity and water retention rate were measured,and they were cured for 3 d,7 d and 28 d respectively,and the mechanical properties were tested.Seven polymers had an impact on the fluidity and water retention of cement mortar.The hydroxypropyl methyl cellulose ether with-OH and the polyacrylamide with-CONH₂could significantly reduce the fluidity of cement mortar by 17.52%and 23.13%,and could increase the water retention rate by 11.08%and 1.58%.The incorporation of polymers was not conducive to the improvement of the compressive strengthof mortar blocks,which was cured for 28 days under natural conditions.The addition of polyvinyl alcohol,hydroxypropyl methyl cellulose ether,polyvinylpyrrolidone,xanthan gum,polyacrylamide,sodium polyacrylate,and guar gum could reduce the compressive strength of mortar blocks by about 68.49%,59.37%,26.54%,16.46%,12.24%,9.55%,and 1.11%,respectively.The impact of polymers on flexural strength was different.Guar gum,sodium polyacrylate,and xanthan gum could increase the flexural strength of mortar blocks by about 0.49%,4.21%,and 26.42%,respectively.However,polyvinyl alcohol,polyacrylamide,polyvinylpyrrolidone,and hydroxypropyl methylcellulose ether reduced the flexural strength of mortar blocks by about 29.82%,3.89%,2.76%,and 1.13%,respectively.