Corrosion-resistant Reinforcement

Fibre-reinforced polymers (FRP) rebars, usually made of an epoxy matrix reinforced with carbon or aramide fibres, have also been proposed both as prestressing wires and reinforcement. Nevertheless, they are not discussed here, because these applications are still in the experimental phase and there is a lack of experience on their durability. In fact, while they are not affected by electrochemical corrosion typical of metals, they are not immune to other types of degradation. FRP are also used in the form of laminates or sheets as externally bonded reinforcement in the rehabilitation of damaged structures this application will be addressed in Chapter 19. 

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Since the formation of the chlorohydrin is accompanied by the production of an equimolar quantity of hydrogen chloride [7647-01 -OJ, the reaction solution is strongly acidic and corrosive. The first chlorohydrin reaction towers were built of stoneware or of mild steel and lined with mbber and ceramic tiles. More recently corrosion-resistant reinforced plastics have been used with good results, but operating pressures must be maintained at or near atmospheric. 

Normally concrete is reinforced with plain carbon steel, but under conditions where rapid carbonation can occur or there is a risk of chloride contamination, corrosion-protected or more corrosion-resistant reinforcing steels may be necessary. Currently there are three reinforcing bars which have enhanced corrosion resistance ... 

Hetron 900 Series. [Ashland/Compos-ite PMymers] Vinyl ester resins for corrosion-resistant reinforced thermosetting idasdc equiinnent... 

Before discussing corrosion-resistant reinforcement, mention will be made of the requirements for reinforcing bars and the characteristics of normal carbon-steel reinforcement... 

I 75 Corrosion-resistant Reinforcement Table 15.2 Different types of prestressing steel [3]... 

D. McDonald, D. Pfeifer, P. Virmani, Corrosion resistant reinforcing bars - findings of a 5-year study , Int. Conf on Corrosion and Rehabilitation of Reinforced Concrete Structures, Federal Highway Administration, Orlando, 7-11 December 1998 (CD ROM). 

The issue of coated and corrosion resistant reinforcement presently seems to be moving in the direction of stainless steel and stainless steel clad reinforcement. The high price of metals on the international markets has held back wider use of stainless steel at the time when its use was starting to be more widely considered. The move to develop new organic coatings for reinforcement seems to have diminished as no clear improvement to fusion bonded epoxy coating has yet emerged. 

Unlike typical polyesters, vinyl esters have no internal ester linkage and, therefore, are less susceptible to hydrolysis. In addition, the great accessibility of the vinyl sites essentially ensures their complete consumption in polymerization reactions. Accelerators, stabilizers, and initiators have also received study for these systems.Isophthalic acid and bisphenol-A based polyesters are in competition with the vinyl esters for the corrosion-resistance reinforced plastics market. 

Protection of reinforced concrete structures against steel corrosion requires careful design and construction practice, exclusion of chloride ion from the concrete through surface treatment and direct prevention of steel reinforcement. In the last case, two approaches are possible to use corrosion-resistant reinforcing steel or to nullify the effects of chloride ions on unprotected reinforcement. 

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