Abstract

The C-S-H gels present in commercial blast-furnace slag and synthetic-slag glass pastes produced by hydrating with 5M KOH solution have been studied by a combination of transmission electron microscopy (TEM) and 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy. They are related by both composition and morphology to the C-S-H gels present in slag-OPC pastes but are more crystalline. The inner product C-S-H is intermixed on a fine scale with a Mg,Al-rich phase with a Mg/Al ratio of ≈2.5. The C-S-H in both inner and outer product contains substituted Al in tetrahedral co-ordination sites. The data are analysed in terms of a model for the structure of C-S-H gel.