On 20 cement pastes made from cements of variable C 3 A and SO 3 contents and cured at different curing conditions the effect of cement composition on the extent of expansion was studied. It appears that the extent of the generated expansion depends especially on the C 3 A and SO 3 contents in cement, but not on theSO 3 3 A ratio. The extent of expansion increases with the amount of water supplied to the cement paste from outside.