Morphology and nanostructure C-S-H in white Portland cement-fly ash hydrated at 85 deg C

The C-S-H present in water and alkali activated hardened pastes of neat white Portland cement (WPC) and blends of WPC with 30% fly ash hydrated at 85 deg C has been characterised. The chemical composition of C-S-H could not be determined by SEM-EDX because of intermixing with other phases; TEM-EDX was necessary. The mean Ca/(Al-Si) atomic ratio of C-S-H was lower in the water activated blend than in the neat cement paste due to the reaction of the fly ash. The fibrillar morphology of outer product C-S-H in the water activated neat cement paste was coarser than that formed at lower temperatures. The mean length of the aluminosilicate anions in the C-S-H was much higher than in C-S-H formed at lower temperatures and was higher in the blended pastes than with neat cement. The composition-structure data are discussed in terms of models for the nanostructure of C-S-H. The lattice parameter a inferred from compositional data for the hydrogarnet phase in the water activated blend was in good agreement with the value measured directly by XRD.