Concrete Deck Reinforcement

Concrete bridge deck slabs, parapets, and sidewalks are often reinforced with mild steel reinforcement bars. In most cases, the reinforcing bars in the concrete bridge deck should conform to the requirements of ASTM A615 or ASTM A706, both with a yield strength of 60 ksi, and modulus of elasticity equal to 29,000 ksi. These deck reinforcement bars are often protected from corrosive materials through the use of an epoxy coating applied to the bars. Alternatively, some agencies require that the deck reinforcement bars be galvanized in an effort to protect the bars from corrosion. Furthermore, some agencies allow the use of uncoated bars in the bridge deck, but provide increased cover to the reinforcement. The choice of corrosion protection is dependent on the environment in which the bridge is located, and the likelihood of corrosive materials being applied to the bridge deck. The designer should refer to standard specifications and design manuals for the particular deck reinforcement and corrosion protection method required by bridge owner.

However, since corrosion of mild steel reinforcement is a main cause of deterioration of concrete bridge decks, other viable reinforcement options have been investigated and used in practice. The use of fiber-reinforced polymer (FRP) reinforcement bars and stainless steel reinforcement bars in concrete bridge decks has increased in recent years, and research using each is currently on-going. Currently, the AASHTO LRFD (7th Edition, 2014) does not explicitly address either reinforcement option.

In addition to superior corrosion resistance, FRP reinforcement bars offer a high strength and light weight alternative to typical steel reinforcement in concrete bridge decks. In the absence of AASHTO or bridge owner specifications, ACI 440.1 R-06 provides design guidance for the design and construction of structural concrete reinforced with FRP bars (9). A recent study discussing the use of a bridge deck reinforced with glass FRP bars built in Vermont offers another resource for designers, as a field investigation is described along with design and construction procedures (10). A higher cost is associated with the use of FRP or stainless steel reinforcement bars in bridge decks, as compared to the use mild steel reinforcement. However, these higher initial costs may be offset by the possible savings in maintenance and repairs over the life of the bridge.

Stainless steel reinforcement bars are manufactured according to ASTM A995, and have enhanced corrosion resistance as compared to conventional reinforcement. The entire reinforcement bar is comprised of a corrosion resistant combination of metals, with a large percentage of chromium and nickel. Stainless steel has a high chloride threshold and a slower corrosion rate than conventional reinforcement. Stainless steel reinforcement is available for yield strengths of 40, 60, and 75 ksi, and in the same sizes as conventional steel reinforcement bars. The use of stainless steel bars may be warranted in a highly corrosive environment, such as a project site in an oceanic location. Like FRP reinforcement, stainless steel has higher initial costs than conventional reinforcement which may be offset by future maintenance savings.