On the possibilities of in situ studies of the hydration of aluminate cements using wideline Al-27 NMR spectroscopy

Wideline Al-27 NMR spectroscopy has been applied to the investigation of the hydration of CA, CA(2) and C(3)A. A selective disappearance of the lower frequency part of the Al-27 NMR line of original CA was observed during hydration. The deconvolution of Al-27 NMR spectra of anhydrous and hydrated CA into a number (6 to 9) of gaussian components allowed for a semiquantitative analysis of the kinetics of hydration of CA. Because of a strong correlation between the components of the line of original CA reliable estimates of the intensities were obtained only concerning the total CA line and its two internal components as well as concerning the amount of aluminate ions in solution and total new hydrated solid products. The kinetics of hydration of CA(2) and C(3)A have been studied using difference spectra of hydrated and anhydrous samples. These difference spectra corresponded to a gradual decrease in the amount of aluminum in the liquid phase and a prolonged induction period in the case of hydration of CA(2). The hydration of C(3)A proceeds without any detectable induction period and new solid was found to crystallize in significant quantities as early as after 10 minutes of hydration. The lines of original solid CA(2) and C(3)A disappear as a whole without observable selective hydration. (C) 1997 Elsevier Science Ltd.