Pore size distribution and degree of hydration of metakaolin–cement pastes

The current paper shows the results of an investigation focussing on the effect of metakaolin (MK) on the microstructure of MK blended pastes. Pastes containing 0%, 10%, 15%, 20% and 25% of MK were prepared at a constant water/binder ratio of 0.55 and cured at 20°C for hydration periods from 1 to 360 days. On the one hand, the total, capillary, and gel porosity evolution with the curing time has been investigated. On the other hand, a method to estimate the degree of hydration in MK/OPC mixes is proposed in this paper. The values of the degree of hydration are calculated from the amount of Ca(OH) 2 present in the paste and from the data of differential thermal analysis (DTA) and thermogravimetry (TG). A good correlation between porosity and degree of hydration has been found.