Effect of the Chemical Nature of Polyvinyl Alcohol on the Microstructure of Cement Hydration Products

The influence of chemical nature of polyvinyl alcohol (PVA) on the microstructure of cement hydration products was investigated. Thermal analysis, X-ray diffraction, Si-29 nuclear magnetic resonance (NMR), and scanning electron microscope were used to explore the microstructure and content of cement hydration products. The pore structure of the matrix was measured by a mercury intrusion porosimeter. Ca(OH)(2) in PVA-modified cement composites showed multidirectional growth, and its platelike structure was distorted due to the intersection of different growth orientations. The decomposition temperature of Ca(OH)(2) in PVA-modified cement composites was lower than in unmodified cement composites, which was greatly affected by degrees of polymerization of PVA. Besides, the mean chain length of calcium silicate hydrate (C-S-H) gels showed an increasing trend with the increase of degrees of hydrolysis and polymerization of PVA, but it was less than that of unmodified cement composites. The incorporation of PVA increased the porosity, but refined the pore-size distribution of the matrix. PVA film between layered Ca(OH)(2) and on the surface of cement hydration products acted as an additional bond and increased the internal cohesion of the matrix.