Corrosion . Corrosion of reinforcement and other embedded steel is 

 considered to be potentially the most serious durability problem although, 

 again, corrosion can usually be controlled by using appropriate materials 

 and procedures.!? J Steel embedded in high-quality dense concrete with a 

 high cement factor is protected in two ways: (1) the high pH environment 

 created by the cement passivates the steel and (2) the concrete's low 

 permeability rate prevents resupply of seawater with dissolved carbon 

 dioxide (which could reduce the pH) and oxygen (which is necessary for 

 corrosion of steel) . Chloride ions penetrate even dense concrete in time 

 periods of months X J When in contact with embedded steel the chloride 

 will decrease passivation protection for a given pH level. However, cor- 

 rosion still does not occur if either the pH is high enough or the rate 

 of permeability (rate of oxygen resupply) is low enough . I? 7 ' 29 J 



Other corrosion prevention methods have been used. Cathodic protec- 

 tion is not considered practical in many large structures since all the 

 reinforcing steel must be electrically bonded together. Metallic (zinc, 

 cadmium) and nonmetallic (epoxy, chlorinated rubber) coatings of rein- 

 forcing and prestressing steel have been tried in the laboratory and in 

 the field with mixed successes. L J Currently, uncoated steel is preferred 

 for both reinforced and prestressed concrete. Uncoated posttensioning 

 tendons are grouted in watertight ducts .t n Galvanizing, if used, should 

 be treated with small amounts of chromate to prevent hydrogen gas for- 

 mation. L J Steel coated with nonmetallic materials must be prepared and 

 handled very carefully (which increases cost) since even a small pinhole 

 in the coating (due to lack of coverage or to a knick or scratch) may 

 cause localized accelerated corrosion. 



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