C.S.Suryawanshi, Former Chief Engineer & Joint Secretary (P.W.D) Senior Consultant, Mumbai.
IntroductionBoth stainless steel and carbon steel derive their corrosion resistance from a naturally occurring chromium rich oxide film, which is present on its surface. This invisible film is inert, tightly adherent to the metal, and most importantly in an environment where oxygen is present, even at relatively low levels, the film reforms instantly if the surface is damaged. There are, however, aggressive environments (e.g., carbonation or ingress of chlorides) which can give rise to breakdown of this passive layer resulting in corrosion of the unprotected surface. When deterioration has developed to a given point, rehabilitation measures are required. Among the various rehabilitation options modern stainless steel has become an attractive alternative when compared to traditional methods with carbon (unalloyed) steel, epoxy coatings, corrosion inhibitors, cathodic protection, etc.
Deterioration of reinforcement is a complex process, where several aspects regarding the concrete, the reinforcement steel, the structural design, and the environment all may have an influence. To find the optimal rehabilitation strategy, it is decisive for the bridge or building owner to include all costs throughout the remaining lifetime of the structure, such as repair costs, maintenance costs, administrative costs, consulting fees, costs of disruptive traffic alterations (road user costs), etc.
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