Investigation regarding the effect of viscosity modifying admixtures upon the Portland cement hydration using thermal analysis

The effect of 13 viscosity modifying admixtures (VMA) on the Portland cement hydration was studied in this paper. In this purpose, thermal analyses (DTA and TG) were performed after 1, 7 and 28 days of hydration on cement pastes containing 0.01–0.5 % from the following VMA: diutan gum, welan gum, polygalactomannane ether, natural cellulose fibres, modified polysaccharide, polyacrylamide, high-molecular mass synthetic copolymer, hydroxypropyl starch and a chemically modified starch. It was noticed that the proportion of Ca(OH)₂ from the samples containing polygalactomannane ether and modified polysaccharide was smaller than in the reference sample, which proved their effect of cement hydration delay. For the other VMA, this effect was not detected, on the contrary, the amount of Ca(OH)₂ was higher than in the reference sample.