Abstract
The use of austenitic stainless steels as rebar is an option increasingly used in reinforced concrete structures exposed to aggressive environments and especially those that have to work in marine environments. The same is true for duplex stainless steel rebars, although nowadays they have a lower use, mainly due to the fact that their inclusion in the reinforced concrete standards was delayed 10 years compared to austenitic stainless steel ones, and consequently their in-service behavior is not as well known. A study of the mechanical properties, including fracture toughness, fatigue behaviour and corrosion resistance in saline alkaline environments of austenitic (AISI 304LN and 316LN) and duplex (D2205) stainless steel reinforcing bars was performed in this work. Bars made on a high ductility carbon steel (B500SD) that are normally used to reinforce concrete were also characterized and used as a comparison. Stainless steel reinforcing bars show mechanical properties at least similar but usually higher than one of the best carbon steel re-bars (B500SD), along with a significantly higher ductility and, of course, much better corrosion behaviour in saline alkaline environments.
Highlights
It has long been recognized that carbon steel reinforcing bars have a low resistance to corrosion in chloride-bearing environments, as it is the case in coastal structures or due to the use of de-iced salts in cold weather conditions
The stainless steel rebars, both austenitic and duplex, analyzed in this work, show a tensile strength, toughness and fatigue resistance, at least similar, and in many cases higher tthan those shown by a carbon steel reinforcement bar with high ductility (B500SD), showing a significantly higher ductility, together with an excellent corrosion resistance in saline environments
Nitrogen -added in this case to achieve a solid solution hardening- and residual elements, such as titanium, must be strictly controlled to avoid the formation of TiN precipitates, and thereby ensure a good fracture and fatigue behavior of the rebars
Summary
It has long been recognized that carbon steel reinforcing bars have a low resistance to corrosion in chloride-bearing environments, as it is the case in coastal structures or due to the use of de-iced salts in cold weather conditions. Concrete provides protection to the embedded steel under the aforementioned conditions, the penetration of oxygen, water and chloride ions through the concrete gives way to a rapid deterioration of the structure. In these cases, there are other methods of protection against corrosion (1), the use of stainless steels as substitutes of carbon steels for the reinforcement of the more exposed zones of the structures is nowadays becoming more and more frequent (2). The use of stainless steels, initially very expensive (stainless steel has nowadays a cost 5-8 times more expensive than uncoated carbon steel), offer cost savings in the long term, eliminating or reducing rebar coatings, the use of thicker concrete overlays, and especially maintenance and rehabilitation costs (3, 4) Today, the use of stainless steel reinforcing bars are considered an optimal construction option when a design life of 75-100 years is demanded and life-cycle cost analysis has to be taken into account (5-7).
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