The effect of natural zeolites on the early hydration of Portland cement

In this work, the effect of zeolite, coming from Pentalofos area, Thrace, Greece, on the hydration of cement is examined. The experimental part comprises three stages: In the first stage a complete mineralogical characterization of the zeolite was performed. In addition, the pozzolanic reactivity of the zeolite was evaluated on the basis of Chapelle test. In the second stage, pastes of Portland cement, incorporating 0%, 10%, 20% and 30% per weight of fine zeolite were prepared. The pastes were water-cured at 20 °C, for 1, 2, 7 and 28 days. Finally, the hydration rate and products were studied by means of X-ray diffraction and Fourier transform infrared spectroscopy, in combination with thermoanalytical methods (TG/DTG and differential thermal analysis). As it is concluded, the examined zeolite consists mainly of “heulandite type II” and shows a good pozzolanic reactivity (0.555 g of Ca(OH)2 per gram of zeolite, according to the Chapelle test). The incorporation of zeolite in cement contributes to the consumption of Ca(OH)2 formed during the cement hydration and the formation of cement-like hydrated products.