Physicochemical Impacts of In-Situ Mineralized CaCO<sub>3</sub> on Very Early Hydration of Cement at Two Temperatures
Sean Monkman, Paul A. Kenward, Greg Dipple
Abstract
The addition of carbon dioxide to ready-mix concrete can improve its performance through in-situ mineralization of calcium carbonate. A model system of an oil-well cement paste mixed with and without additions of CO 2 gas was investigated to characterize the impacts of in-situ CO 2 mineralization on the first 15 min of hydration at 4 and 24 °C. Impacts were examined through aqueous chemistry, total inorganic carbon (TIC), stable isotope 13 C/ 12 C fractionation, loss on ignition (LOI), and scanning electron microscopy (SEM). It was demonstrated that the calcium and silicon concentrations increase immediately after the CO 2 input and declined within the first few minutes. TIC testing confirmed that the mineralization was rapid and brief with no evidence of increasing carbonate formation in the minutes after the CO 2 input. Isotope fractionation confirmed that the carbonates formed were attributable to the mineralization of gaseous CO 2 . The loss on ignition testing showed that the CO 2 -activated system had greater mass gain (bound water and bound CO 2 ) over 15 min of hydration than did the reference. SEM observations identified carbonate reaction products <200 nm immediately after the CO 2 injection. Gel products were formed over the ensuing 15 min. The temperature of the testing had little impact other than to increase the concentrations of Ca and Si in solution and increase the amount of mineralized CO 2, as associated with the higher solubility of CO 2 in water as the temperature decreases.