The kinetics of cement hydration can be accelerated by steam curing and this kind of curing can be responsible for increasing concrete porosity, since a greater portion of non hydrated cement particles can be present. The increased porosity results can result in increased permeability. The aim of this work was to investigate the influence of curing on concrete quality by air permeability and compressive strength test. It was measured by means of a non steady state air permeameter. Concretes were produced with Portland cements containing 0%, 27% and 53% of ground granulated blastfurnace slag. The amount of slag in cement influenced concrete performance and steam curing increased air permeability of concrete.