Influence of the kind of mineral addition and the seawater on the hydration of a portland cement

The influence of two pozzolanic additions, a calcined clay and a zeolitic tuff, on the hydration of a Portland cement was studied in pastes prepared with fresh water and substitute seawater. The pastes contained 0, 5, 10, 20 and 30% of each pozzolanic addition and were prepared with a water–to–solid ratio of 0.50. The hydration kinetic was evaluated by isothermal calorimetry at 30 °C and during 72 h. The bound chloride contents in the pastes were also quantified. The results of the experiments indicated that there was not a correlation between the kind of mixing water and the induction periods but these periods increased with the percent of substitution of the Portland cement and the increments were higher with the finest pozzolan and with the higher content of alumina containing phases (calcined clay). It was observed that during the acceleration periods the mineral additions increased the reaction rates and the release of heat during the principal peaks and the increments were higher in pastes with the calcined clay and in those prepared with artificial seawater. The total cumulative heats were higher in the systems where the Portland cement was substituted by the calcined clay (with higher content of alumina) and in the pastes that were prepared with substitute seawater. The capacity to bind chloride was related to the content of Al₂O₃ y Fe₂O₃ in the mineral addition and it was higher in pastes with calcined clay (with higher content of Fe₂O₃ and Al₂O₃ containing phases) but the zeolitic tuff was more effective to bind chlorides, in spite of having less quantity of phases providing Fe₂O₃ and Al₂O₃.