Results of X-ray investigations on hydration products of cementitious materials using special specimen holders and preparation techniques

Hydration products of calcium silicates and calcium aluminates often are difficult to identify by X-ray methods. In this study the hydration products of the aluminate phase especially under the influence of additional chloride ions were studied. Special X-ray measurement conditions must be applied for accurate identification including 1. In situ control of relative humidity 2. Exclusion of CO2 from air 3. Facilities for easy sample access and exchange 4. Temperature control Proper conditions allows one to distinguish between several chloride containing hydration products of the aluminate phase of cement. For this investigation, a special climate chamber and a high temperature furnace with controlling atmosphere facilities was used. INTRODUCTION Lamellar calcium aluminate hydrates are mainly formed in the process of the cement hydration and can incorporate different anions in the layer structure (Auer (1992), Kuzel(1966) , Pöllmann(1990), Wenda(1984)). The structure of several of the compounds has been determined. The chloro-compound, called „Friedel ́s salt or monochloride“ was determined by Terzis,A., Fillipakis,S., Burzlaff,H. & Kuzel,H.-J. (1987). The structure is composed of a main layer of Ca 2 [Al(OH)6 ] + and an interlayer of [ Cl . nH2O ] . A structure and the coordination polyhedra for the monochloride are shown in Figure 1. This structure forms by hydration of the aluminate phase of cements and by the influence of chlorine containing brines on cement hydration products. For this reason it is useful to investigate the different chlorine containing phases and to determine the potential of chlorine bonding. By using special equipment it is possible to characterize the different hydrates in detail. It can be shown that for monochloride the following parameters can be determined with high accuracy : 1. Phase transformation : monoclinic hexagonal at 30C 2. Stacking faults of layer structure 3. Coincidences of (00l)-reflections 4. Preferrential orientation 5. Complex solid solution series 6. Super structures due to oriented intercalation of interlayers 7. Carbonization reactions 8. Different hydration stages due to water loss of interlayer water 9. Time dependent reactions 10. Water content of phases due to relative humidity Copyright (C) JCPDS-International Centre for Diffraction Data 1999 668