Ceramics-Silikáty 46 (4) 152-158 (2002)

THE EFFECT OF WATER RATIO ON MICROSTRUCTRE AND COMPOSITION OF THE HYDRATION PRODUCTS OF PORTLAND CEMENT PASTES

T. Slamečka, F. Škvára

The study was concerned with examining the effect of the water-to-cement ratio over the range of 0.19 to 0.50 on the composition and morphology of hydrated cement pastes. The strength after setting increases with decreasing w/c while the content of hydration products decreases. At the same time the homogeneity of the hydration products tends to increase and the occurrence of crystalline hydrates (particularly that of portlandite) decreases. At the lower w/c values, higher-calcium forms of the C-S-H phase, in which Ca(OH)₂ is dispersed, arise at the lower w/c values. Crystalline portlandite exhibits a preferen-tial direction of fracture, thus creating conditions for potential ready crack propagation and therefore also for a possible lowering of strength. Crystalline Ca(OH)₂ is then the weakest part of the set system and represents a limit of its mechanical properties. The differences in the content and form of Ca(OH)₂ present in set materials based on Portland cement may have unexpected effects on their performance properties.

Keywords: Microstructure, Hydration, Low porosity, Portlandite, Portland cement