Bridges steel reinforcements

In principle, stainless-steel reinforcement can be a viable solution for preventing corrosion in a large number of applications. The chloride threshold is much higher than the chloride content that is normally found in the vicinity of the steel even in structures exposed to marine environment or de-icing salts. There is no objection to using stainless steel only where its improved protection is necessary, combined with normal steel at other areas. Hence, stainless-steel bars can be used in the more vulnerable parts of structures exposed to chloride environments, such as joints of bridges or the splash zone of marine structures. Similarly, they can be used when the thickness of the concrete cover has to be reduced, such as in slender elements. 

Other materials include treated timber, reinforcement steel, reinforcement fibers, epoxy-based materials, cathodic protective coatings,pipes, and bridge deck sealers. Use of such materials brings additional chemicals (hke creosote, ammoniacal-copper-zinc-arsenate or ACZA, and copper-chromated-arsenate, or CCA). 

The use of cathodic protection for the protection of the internal surfaces of process equipment in the chemical process and in the pulp and paper industries, the protection of water boxes and condenser tube sheets in the electric power industry [53], and the protection of steel reinforcing bars in concrete in highway bridges and parking garages, clearly reveal that this technique is used in a broad variety of appHcations. 

Nevertheless, corrosion of steel reinforcements does occur in structures such as concrete bridge decks and parking garages. These problems have been studied for many years and result from the breakdown of passivity caused, for example, by salt in the environment or in the concrete [59]. Passivity may also be lost after several years if air diffuses through the concrete to the reinforcements, converting alkaline Ca(OH)2 to less alkaline CaCOs. Corrosion processes for steel in concrete are illustrated in Fig. 7.15 [60]. 

There are several methods that can be used to control corrosion of steel reinforcements in concrete. First, the design of the structure should provide for drainage of salt-containing waters away from the reinforced concrete. Second, concrete of adequate thickness, high quality, and low permeability should be specified to protect the reinforcements from the environment. Third, chloride content of the concrete mix should be kept to a minimum. For further protection, the steel reinforcements can be epoxy-coated. In many parts of North America, steel reinforcements used in bridge decks are now epoxy-coated as a standard construction procedure. Cathodic protection is also being used, both with impressed current anodes and with sacrificial anodes [61]. (See Chapter 13.)... 

Reinforced concrete deteriorates with time due to corrosion of the steel reinforcement and environmental effects on the concrete, excessive loading due to earthquakes and wind, coupled with increased loads on, say bridges, due to heavy traffic. These situations necessitate repairs. When steel had been used previously, there were a number of attendant drawbacks such as increased weight of steel—the steel plates had to be welded together—and there was considerable increase in overall thickness due to the protective jacket of concrete. 

Triethanolamine is used in the cement and concrete industry to increase the grinding efficiency of cement aggregate to produce free-flowing cement particles. Triethanolamine acts as a dehydration agent when added to concrete and reduces the set time of concrete by as much as 50%. Triethanolamine is the additive of choice for prestressed concrete, bridge deck coatings, and highway construction work. Calcium chloride, a widely-used concrete set accelerator, is corrosive to steel, and can not be used in steel reinforced applications. 

In the particular case of the apphcation of glass-fibre reinforced vinylester composites as internal reinforcement for concrete bridge deck slabs, the results showed their superior fatigue performance and longer fatigue life when compared with the steel-reinforced ones (El-Ragaby et al., 2007). 

Fahmy, M.F.M., Wu, Z.S., Wu, G., and Sun, Z.Y. (2010b). Post-yield stiffnesses and residual deformations of RC bridge columns reinforced with ordinary rebars and steel fiber composite bars . Journal of Engineering Structures, 32 2969-2983. 

Steel reinforced elastomeric bearings rely upon the Inherent shear flexibility of the elastomeric layers to accommodate bridge movements in any horizontal direction. The steel shims limit the tendency for the elastomeric layers to bulge laterally under compressive load, thus limiting vertical deformation of the bearing. The shear flexibility of the elastomeric layers also allows them to accommodate rotational demands induced by loading. 

FIGURE 1.1 Steel reinforced elastomeric bearing (concrete bridge) application. 

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