OPAL SILICA BEHAVIOR IN HIGH PH MEDIUM

The temporal evolution of an amorphous silica, the diatomit used as ch arge in the cement, in an alcali-reaction at different temperatures wa s studied in the liquid phase with a ''bilan de masse'' and in the pri mary and neoformation solid phases by electronic microscopy, X-ray dif fraction and N.M.R resonance of Si-29 NMR spectroscopy. The diatomit i s transformed from the beginning of the reaction and the neoformation solid phase is calcium silicates hydrates with a chain structure showi ng two kinds of Q(2) entities.