ABSTRACT
INTRODUCTION When carefully designed, detailed and constructed, reinforced concrete is extremely durable. The reinforcing steel is protected from corrosion by the alkaline concrete environment. However, if the passive layer surrounding the steel breaks down, for example due to penetration of chlorides, corrosion will take place. The resulting rust occupies a volume many times that of the parent metal, cracking and eventually disrupting the concrete protecting the steel. This form of damage can be a significant problem in aggressive environments, particularly in the case of poor workmanship or poor detailing. Examples of structures that may be particularly at risk include marine structures and bridges subjected to deicing salts. The traditional approach adopted by design Codes to overcoming the problem is to use large covers, with relatively high cement contents, and to limit crack widths. However, increasing the cover, while still maintaining a limiting crack width is self-defeating, resulting only in an increasingly limited stress in the reinforcing steel and a lowered load-carrying capacity. In addition, reinforcement is often provided in concrete in situations where it is needed only to control cracking due to shrinkage and early thermal effects. This leads to the paradoxical situation that the reinforcement is required to control cracking but the main reason for limiting the crack width is to protect the reinforcement.
