The premature failure of corroded steel reinforcements and the expansion of the iron corrosion products around the rebars are amongst the main causes of the concrete degradation. The carbon steel of rebars is protected from oxidation by atmospheric oxygen by the high pH of concrete interstitial water.
The degradation of concrete is primarily caused by the premature failure of corroded steel reinforcements and the expansion of iron corrosion products around them.  The high pH of the concrete's interstitial water protects the carbon steel rebar from oxidation, which helps to prevent this deterioration.