Some cementitious materials cured at elevated temperature may expand on subsequent exposure to moisture. Concern has been expressed as to the relevance of small laboratory specimens to field concretes, in particular due to the potential leaching of ions into the storage solution. The work presented here aims at investigating this effect. Mortars cured at elevated temperature in identical fashion were subsequently stored at 90-100% relative humidity (RH) and in water, a LiOH solution, and KOH solutions of various concentrations. The largest and most rapid expansion occurred with mortars immersed in water. The samples stored at 90-100% RH expanded more slowly. Expansion was even slower when subsequent storage was in LiOH or KOH solutions. The same samples were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). These techniques indicated that ettringite had formed over time in all samples, with little apparent relation to the degree of expansion. The composition of the C-S-H gel changed over time, differently for the different storage conditions. © 2001 Elsevier Science Ltd.