Dimensional stability of 1·4 nm tobermorite, jennite and other layered calcium silicate hydrates

Length-change measurements of 1·4 nm tobermorite, jennite and calcium silicate hydrate preparations (with varying calcium/silicon ratio) subjected to drying from the 11% relative humidity condition are reported. The dimensional stability investigation is focused on the role of adsorbed and interlayer water as shrinkage mechanisms involving menisci effects in capillary pores are eliminated in this humidity range. Length change against mass loss curves and the corresponding d₀₀₂ basal spacing change (obtained by X-ray diffraction) with mass loss are assessed and inferences drawn regarding nanostructural models for calcium silicate hydrates in hydrated Portland cement paste. Length changes of the pure phases were significantly greater than those for hydrated cement paste due to the restraining effect of unhydrated cement particles and calcium hydroxide crystals in the paste. The dimensional stability and the role of the removal of ‘structural water' from the systems studied are discussed in terms of its relevance to cement-based materials.