Some questions on the corrosion of steel in concrete - Part I: When, how and how much steel corrodes

It is widely accepted that concrete-embedded steel is in a passive state. However, there are some exceptional circumstances that induce corrosion in an active state within concrete structures, thereby severely reducing their durability. This two-part paper analyses some major questions which, however elementary they may be, are still controversial in scientific, technical and economic terms. The first part provides answers to the following questions on the steel/concrete/environment system: 1) How does steel in concrete normally behave? 2) What are the initiating factors for depassivation? 3) What are the effects of corrosion? 4) What is the morphology of corrosion in the active state? and 5) What is the corrosion rate threshold above which the durability of reinforced concrete structures is impaired? The answers to these questions are provided in light of experimental results, most of which were obtained by the authors themselves.