When it comes to building or repairing reinforced concrete structures so that life-cycle costs are minimized, many authorities are specifying the use of stainless steel reinforcing bars (rebars) instead of the traditional carbon steel rebars, according to the Nickel Institute. Nickel improves the mechanical properties of stainless steels and helps to boost their corrosion resistance. Commonly speciﬁed alloys for stainless steel rebar are Type 304 ,Type 316, Type 316 LN, 2304 and 2205.
These alloys can provide long-term corrosion resistance when concrete is exposed to chloride-containing environments, e.g., road salt and sea water. They have been used as rebar in highway bridges, ramps and barrier walls, parking garages, tunnels, sea walls and marine facilities, building foundations and restorations. In Europe, Ni-containing stainless steel rebars have been widely used since the 1980s. In North America, their use in highway bridges has been steadily growing since the mid 1990s, with many large bridges being constructed or extensively repaired.
The US Federal Highway Administration (FHWA) organized extensive corrosion testing to ﬁnd rebar materials that could extend the lifetime of reinforced concrete bridges to 75-100 years, when the concrete was contaminated with chlorides. Their 1998 report (FHWA-RD-98-153) concluded that stainless steel rebars, like Type 316, would be capable of providing that required lifetime.
Stainless steel rebar is substituted for carbon steel rebar only in critical parts of the structure that will experience corrosive conditions. For bridges, experience has shown that the total project cost increase when using stainless steel rebar can be 3 percent, or less. The actual cost increase will depend on the size and complexity of the bridge design. The use of stainless steel rebar is predicted to extend the useful life of the structure to 75-100 years, with the consequent savings on repairs and/or early replacement.
Stainless steel rebars are produced according to ASTM A955. Depending on the stainless steel grade selected, yield strengths > 75 ksi (520 MPa) and tensile strengths > 100 ksi (690 MPa) can be achieved. Stainless steel rebars also have superior toughness, ductility and fatigue resistance. These properties are beneﬁcial in earthquake-prone regions and in low temperature applications.
The use of Ni-containing stainless steel rebar is expected to continue to increase as Federal, State, Provincial and local governments demand much lower maintenance costs, fewer disruptions and longer lifetimes for their bridges and other important concrete structures. Along with stainless rebar, other stainless steel components such as tie-wire, rebar couplers, dowels and welded-wire mesh are available to complete the corrosion resistant system.
Source: The Nickel Institute