This paper investigates the effect of different conditions on the development of concrete expansions due to alkali-silica reaction (ASR), delayed ettringite formation (DEF) and their combination. The presence of products of the two reactions has been observed during structure diagnosis. The aim of this research is to study the two reactions in concretes with close mix designs but with various types of aggregate and moisture conditions. Measurements performed in the three directions of stress-free specimens showed that DEF expansions could be considered as isotropic for stress-free material. DEF expansions were largely influenced by the storage conditions (immersed in water or in sealed conditions). The volume of storage water modified the kinetics. Under sealed conditions, no expansions were measured for mortar containing non-reactive aggregate, while small positive strains were obtained for mortar containing reactive aggregate. In all cases, new water supply caused fast, large expansions. The different effects of alkali leaching and moisture conditions on DEF and ASR expansions are discussed. (C) 2011 Elsevier Ltd. All rights reserved.