Service life predictions for concrete exposed to chloride-induced steel corrosion usually result from durability tests done on uncracked concrete. The almost natural presence of cracks is not taken into account. A chloride migration coefficient for uncracked concrete could only be used if the structure can be considered as uncracked. This research shows the effect of crack width limitation on chloride migration in concrete. The maximum crack width allowed should be less than 0.1 mm to have the seemingly uncracked condition. The extra amount of steel needed to achieve a crack width of 0.05 mm in a concrete slab results in a 35-43% increase of the global warming potential. The slab is preferably made of fly ash + silica fume concrete because of its low 28 day chloride migration coefficient (3.4 × 10-12 m²/s), its long expected service life (> 100 years) and its ability to partially heal 0.1 mm cracks.