Control of hydration rate of polymer modified cements by the addition of organically modified montmorillonites

The addition of polyvinyl alcohol (PVA) in concrete causes a delay in the hydration rate of Portland cement paste. Three different montmorillonites (MMTs) (Cloisite Na, 30B, and Nanofil) were previously mixed with PVA in order to control this delay. A comparison between the hydration rate of Portland cement paste and Portland cement paste modified with PVA and the different MMTs was made by means of semi-adiabatic calorimetry, thermal gravimetric analysis and contact angle measurements. Different rates of hydration were obtained with each MMT. The paste with PVA and Nanofil behaves almost the same as the unmodified cement paste. Mechanical properties were also studied. An increase in the flexural strength and a decrease in the compression strength were found, which is expected for a Portland cement paste modified with PVA. The addition of MMT to the cement paste with PVA hardly affects the mechanical properties.