ON THE POSSIBILITIES OF IN-SITU STUDIES OF THE HYDRATION OF ALUMINATECEMENTS 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 obse rved during hydration. The deconvolution of Al-27 NMR spectra of anhyd rous and hydrated CA into a number (6 to 9) of gaussian components all owed for a semiquantitative analysis of the kinetics of hydration of C A. Because of a strong correlation between the components of the line of original CA reliable estimates of the intensities were obtained onl y 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 s amples. 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 proce eds 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 Scien ce Ltd.