Solid state NMR investigations on the role of organic admixtures on the hydration of cement pastes

The influence of different inorganic additives and organic admixtures on the hydration and hardening of Portland cement (CEM I 42.5R) were studied on a nanometer scale by advanced solid state NMR methods. Added quartz was found to be partially attacked by the alkaline media of the cement paste. Even small amounts of organic admixtures strongly influence the hydration and crystallization process of the cement paste. Methyl cellulose, poly(vinyl acetate co vinyl alcohol), poly(ethylene oxide), poly(acrylic acid) and poly(acrylamide) modify the hydration of the calcium aluminum oxides. Major changes in the inorganic structure were detected for low amounts of citric acid and tartaric acid which suppress silicate condensation and strongly alter calcium aluminum oxide hydration. Within this study several solid state NMR methods like 1D magic angle spinning (MAS), 2D exchange and 2D double quantum NMR were applied for the detection of ¹H, ²⁷Al and ²⁹Si nuclei. Thus, cement pastes, inorganic additives and organic admixtures could be monitored individually. The findings on a molecular level as provided by NMR are related to changes in the mechanical properties of the cement pastes.