International Journal for Restoration of Buildings and Monuments vol:13 issue:3 pages:153-160
Modification of cement mortars with small amounts of water-soluble polymers (1% of polyvinyl alcohol-acetate, methylcellulose or hydroxyethylcellulose) is studied. The effect of water-soluble polymers on the microstructure is twofold: cement hydration reactions can be influenced and polymer films or bridges can be formed. Cement hydration is studied at several time intervals by means of thermal analysis, XRD and FT-IR. The addition of small amounts of hydroxyethylcellulose strongly retards the cement hydration during the first 24 hours of hydration. After 48 hours, this delay is almost eliminated. Polymer modified mortars show a slightly higher amount of bound water than unmodified mortars. Nevertheless, the Ca(OH)2 content is decreased by polymer modification.
SEM investigation is used to characterize the morphology of the cement hydrates. A large crystal growth is noticed at the air void surfaces, where the presence of water-soluble polymers is expected because of their strong affinity to the gas-water phase. Mortars modified with methylcellulose, a polymer with a high swelling capacity, show an abundant Ca(OH)2 efflorescence. Undistorted layers of Ca(OH)2 crystals are formed and polymers are found to form additional bridges between those Ca(OH)2 crystals.