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 correlations of experimental determinations of the degree of hydration of alite 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 calculations; the phase composition obtained by use of the Bogue, Taylor's modified Bogue, and quantitative X-ray diffraction methods gave rise to some differences in the results obtained. Ca/Si ratios determined using the Bogue composition were consistently lower than those from Taylor's method and the quantitative X-ray diffraction analysis methods for both the Portland cements studied. The Ca/Si ratios estimated based on the mineralogical phase compositions determined from these latter methods agreed well with those from energy dispersive X-ray spectroscopy measurements.