Rheology of portland cement pastes with siliceous mineral additions

In this paper, the rheological behaviour of pastes of Portland cement and different siliceous mineral additions was analyzed. For this purpose, two Portland cements with different mineralogical composition (low C3A and high C3S content and low C3S and high C3A content) combined with different replacement percentages of three minerals additions of siliceous nature (quartz, diatomite and silica fume) are used. Mineral admixtures have similar chemical composition, but they have different crystallinity and morphology: the quartz is fully crystalline; diatomite and the silica fume are vitreous with a small fraction of cristobalite. The vitreous phase content in the mineral additions gives the pozzolanic properties. All determinations were performed on Haake Roto Viscosimeter at 25°C, at the time corresponding to the minimum in dQ/dt calorimetric curve during the dormant period. The results show that portland cement with low C3A content and high C3S content presents a great shear resistance and the replacement by siliceous mineral addition affect the rheological behavior of paste depending on the water demand and the pozzolanic reactivity.