Properties and hydration of blended cements with calcareous diatomite

In this paper the effect of diatomite addition on blended cement properties and hydration was studied. Calcareous diatomaceous rocks of Zakynthos Island, Ionian Sea, containing mainly CaCO₃ and amorphous silica of biogenic origin with the form of opal-A were used. Cement mortars and pastes, with 0%, 10%, 20% and 35% replacement of cement with the specific diatomite, were examined. Strength development, water demand and setting time were determined in all samples. In addition, XRD, SEM and weight loss at 350 °C were applied in order to study the hydration products and the hydration rate in the cement-diatomite pastes. Blended cements, having up to 10% diatomite content, develop the same compressive strength, as the corresponding Portland cement, while the presence of diatomite leads to an increase of the paste water demand. Diatomite is characterized as natural pozzolana, as it satisfies the requirements of EN 197 1 concerning the active silica content. The pozzolanic nature of the diatomite results to the formation of higher amounts of hydrated products, specifically at the age of 28 days.