EFFECTS OF THE SECONDARY MINERALS ON THE POZZOLANIC ACTIVITY OF CALCINED CLAY: CASE OF QUARTZ

Abstract

This study aims to document the potential effect of quartz as a secondary mineral on the pozzolanic activity of local kaolinitic clay (from the region of Tabarka, Tunisia). Purification of clay was carried out using the centrifugation process in order to decrease the rate of secondary minerals. Our research was based on two samples: a crude sample and a centrifuged one, and both of them were characterized by several methods. The pozzolanic activity of the two samples was evaluated by compressive strength measurements in mortars containing calcined clays, lime and sand.. In addition, the identification of the hydrated phases in pastes was done by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The comparison between crude and centrifuged samples through this analysis associated with laser granulometry showed that the presence of quartz with particle size lower than 20 μm contributed to the pozzolanic reaction: the pozzolanic activity of the crude sample with high content of quartz was higher than that of the centrifuged sample. The results of the last part of the paper proved the pozzolanic reactivity of crystallized quartz with fineness 20µm, the introduction of 10% of grinding quartz as Portland cement replacement improved the cement paste compactness by increasing compressive strength and hydration.