Indirect determination of the Ca/Si ratio of the C-S-H gel in Portland cements

An alternative method for the indirect determination of the Ca/Si ratio of the C-S-H gel in Portland cements is proposed. It is based on graphical cor relations of experimental determinations of the degree of hydration of alit e and the amount of calcium hydroxide formed with theoretical data based on the hydration reactions of the alite and belite present in the cement. The initial composition of the cements is of prime importance in these calcula tions; the phase composition obtained by use of the Bogue, Taylor's modifie d Bogue, and quantitative X-ray diffraction methods gave rise to some diffe rences in the results obtained. Ca/Si ratios determined using the Bogue com position were consistently lower than those from Taylor's method and the qu antitative X-ray diffraction analysis methods for both the Portland cements studied. The Ca/Si ratios estimated based on the mineralogical phase compo sitions determined from these latter methods agreed well with those from en ergy dispersive X-ray spectroscopy measurements. (C) 2000 Elsevier Science Ltd. All rights reserved.