Influences of Different Admixtures on the Drying Shrinkage Characteristics of Metakaolin-based Geopolymer Mortar

To investigate the influences of different admixtures on the drying shrinkage of polymer mortar in a metakaolin base, the experiments of VAE (vinyl acetate ethylene copolymer), APAM (anionic polyacrylamide) and CPAM (cationic polyacrylamide) on the drying shrinkage properties of geopolymer mortar were designed under normal temperature curing conditions. An SP-175 mortar shrinkage dilatometer was introduced to measure the dry shrinkage of geopolymer mortar. Meanwhile, the drying shrinkage properties of geopolymer mortar are exhibited by the parameters of water loss rate, drying shrinkage rate, drying shrinkage strain and drying shrinkage coefficient. The experimental data are further fitted to obtain the prediction model of dry shrinkage of geopolymer mortar, which can better reflect the relationship between dry shrinkage rate and time. Finally, the experimental results demonstrate that the dry shrinkage of geopolymer mortar can be significantly increased by adding 4% VAE admixture, meanwhile under the condition that the polymer film formed by VAE reaction can strengthen and toughen the mortar. 2.5% APAM admixture and 1.5% CPAM admixture can enhance the dry shrinkage performance of geopolymer mortar in a certain range.