Length change characteristics of Ca(OH) 2 compacts on exposure to water vapour

The presence of large quantities of Ca(OH) 2 in hydrated Portland cement suggests that a study of the length change‐sorption characteristics of Ca(OH) 2 in the form of compacts should provide useful information. Length change‐sorption data were obtained for water from 0 to 76% RH and various cycling experiments between 0 to 58 and 0 to 93% RH were performed during which length change data were obtained. Preliminary experiments were also performed in relation to the carbonatation of Ca(OH) 2 compacts. Large irreversible shrinkages were observed while repeatedly determining the isotherms during the cycling experiments and it is suggested that these were the result of ionic diffusion from the points of contact of crystallites and the pulling together of these crystallites by van der Waals forces. The carbonatation of calcium hydroxide also produced shrinkage and it is considered that this could also be due to van der Waals surface forces.