Quantitative X-ray diffraction of free, not chemically bound water with the PONKCS method

Abstract

The free water in calcined phyllosilicate–water mixtures exhibits a distinctly different behaviour in its X-ray amorphous scattering contribution as opposed to fly ash– or limestone powder–water mixtures. While fly ash and limestone powder yield a continuous increase in the scattering contribution when water is added, the scattering contribution stagnates for calcined phyllosilicates over a wide range of water addition. There is a direct correlation between the consistency of the sample and the X-ray amorphous scattering contribution caused by the water. The same correlation can also be found in in situ X-ray diffraction measurements of hydrating systems. As long as the sample has a pasty consistency, the scattering contribution of the water decreases with progressive reaction. After the transition from fresh paste to final set, there is no further reduction of the X-ray amorphous scattering contribution caused by the free water, which means that the free water cannot be quantified correctly from this point in time.