Principles of corrosion of steel in concrete structures

At potentials and pH levels normally measured in the concrete, a protective passive layer forms on the surface of the carbon steel. It is known that this layer is an ultrathin (<10 nm), protective oxide or hydroxide layer that decreases the anodic dissolution rate to negligible levels. However, the partial or complete loss of the passive layer, known as depassivation, may, under some conditions, lead to active corrosion of the steel bars. Loss of passivation of steel in concrete is almost always caused by either chloride ions or carbonation exposure. The steel sectional loss may impair the serviceability and load-bearing capacity of structures. Additionally, the formation of corrosion products can cause cracking and further deterioration in the concrete. This chapter discusses the basic and essential mechanisms of the corrosion of the reinforcing steel bars in a concrete environment. Subsequent chapters discuss alternative reinforcing materials, the characteristics of concrete that influence rebar corrosion, prevention, and remediation techniques, and, finally, modeling of the rebar corrosion process.