Composition, morphology and nanostructure of C–S–H in white Portland cement pastes hydrated at 55 °C

The C–S–H present in water- and alkali-activated hardened pastes of white Portland cement hydrated at 55 °C has been characterized. The mean length of the aluminosilicate anions in the C–S–H was similar in both systems and increased with age. Inner product C–S–H generally had a fine scale, homogeneous morphology. Outer product C–S–H was generally fibrillar with water, and foil- or lath-like with alkali. There were some regions of C–S–H with coarse morphology. It was not possible to determine the chemical composition of C–S–H using the SEM; TEM–EDX was necessary. The C–S–H formed in the alkali-activated paste had a lower mean Ca/(Al + Si) ratio than that formed with water, which was offset by a larger quantity of calcium hydroxide. The potassium in the KOH-activated paste was present either within the C–S–H structure charge balancing the substitution of Al3+ for Si4+, or adsorbed on the C–S–H charge balancing sulfate ions.