In Situ 27Al NMR Studies of Cement Hydration: The Effect of Lithium‐Containing Setting Accelerators

Abstract

Hydration of calcium aluminate cements is known to cause phase transformations during which the coordination number of aluminum by oxygen changes from 4 to 6. Systematic 27Al magic angle spinning and wide‐line nuclear magnetic resonance (NMR) experiments at 78.3 MHz with detailed attention to the quantitative aspects of quadrupolar NMR spectroscopy show that the fraction of Al(6) is a monotonic function of the water/solid (w/s) ratio and does not depend on the type and concentration of setting accelerators. In situ 27Al wide‐line NMR measurements during the hydration process can provide good estimates of the induction period and the rate of the phase conversion. Using this approach, lithium carbonate at a concentration of 0.5 wt% of the mixing solution has been shown to eliminate the induction period but to leave the rate of the phase conversion essentially unchanged.