Effects of water-cement ratio, quantity and fineness of sand on the evolution of lime in set portland cement systems

The water-cement ratio and the quantity and fineness of sand are shown to influence the evolution of lime in set portland cement systems. Increasing the water-cement ratio from 0.30 to 0.50 caused an increase in Ca(OH) 2 content in both portland cement pastes and mortars at all ages of hydration. For the same water-cement ratios, however, the calcium hydroxide content of the mortars were found to be significantly higher than those of the pastes. With finer sand fractions and higher sand dosages, the rate of precipitation of lime in the mortars also increased. The results have been interpreted on the basis of a ‘through-solution’ mechanism of formation of CH in which after the hydrolysis of the calcium silicates C 3S and C 2S, calcium hydroxide precipitates out of solution as crystals. With respect to the mortars the sand particles are believed to act as a ‘sink’ for the CH crystals which precipitate out of the pore solution. With increasing water content the Ca 2+ and OH − ions become easily transported through the aqueous phase to the inert sand surfaces where favourable thermodynamic conditions exists for crystallization and growth of the Ca(OH) 2 crystals.