Crack width limitation (<0.5mm) = control reinforcement corrosion?

In many standards and code of practice of numerous countries, allowable size of crack width is generally limited to less than 0.5mm for reinforced concrete structure to improve the durability of concrete. The limitation of crack width can serve aesthetic reason on one hand and to achieve durability requirement by avoiding possible corrosion of steel reinforcement instead. Regarding the latter objective, site surveys and experimental evidence don't seem to be in favour of proposition. Beeby showed that there wasn't any correlation between surface crack width (<0.5mm) and durability of reinforced concrete structure. In practice most corrosion problems are triggered by presence of surface cracks parallel to reinforcement in place of surface cracks perpendicular to reinforcement.