Effect of grinding on the quantification of bound water in tricalcium silicate

The effect of grinding hydrated tricalcium silicate (C₃S) pastes on the bound water content (BWC) measured by thermogravimetric analysis was investigated. The samples were subjected to different curing regimes at 20°C and 40°C at a constant water to cement ratio of 0·5. Hydration reactions were stopped using a freeze drier. To study the effect of grinding, samples were either roughly crushed or finely ground. Although the amount of water measured from the dehydroxylation of portlandite was not affected by grinding, the total BWC increased with grinding. This increase in the measured BWC was not affected by the studied curing regimes and degrees of hydration of C₃S. Fine grinding before hydration stoppage using a freeze dryer produced a BWC similar to that of crushed samples. It is proposed that the increase in measured BWC after grinding is due to the confinement of physically bound water in the interlayers of calcium silicate hydrate.