(566o) Effect of Glycolic Acid on Hydration of Tricalcium Silicates – a Combined Experimental and Molecular-Scale Computational Study

Tricalcium silicate is the most abundant constituent of ordinary protland cement and its hydration is largely responsible for early strength development in concrete.  Modern concrete contains not only cement but frequently also includes a variety of organic compounds that are used to modify one of any number of fluid or hardened properties.  One class of such compounds is used to alter the rate of hydration.  Glycolic acid, a well-known hydration inhibitor, is thought to interfere with calcium hydroxide precipitation, a by-product of tricalcium silicate hydration, and thus obstructs the rate of reaction.   Little actual experimental evidence, however, in support of this or other hypothesis is available.  A combined experimental and computational study has been done in an effort to elucidate this mechanism.  Both a semi-empirical quantum mechanical (Parametric Method 3) and a force field method (CLAYFF) were employed for computational study. The recently developed semi-empirical force field CLAYFF considers flexibility of surface OH groups from calcium hydroxide and allows energy-momentum transfer between interfaces. The primary focus is to calculate the interaction energy (binding energy) of glycolic acid on the calcium hydroxide surface. X-ray, calorimetric and microstructural characterization were also used to elucidate the process and support the computational work.