[ Building & Construction ]
[ Building & Construction ]
Adhesion of stainless steel rebar after elevated temperatures due to fire
Before the 1980s , the durability of reinforced concrete did not receive special attention , with most standards simply specifying a minimum concrete cover for steel reinforcement as a precautionary measure . For example , the 1978 CEBFIP model specification , the precursor to the first draft of Eurocode 2 ( EN 1992-1-1 ), did not explicitly address durability issues . However , various corrosion problems in bridge steel bars due to de-icing salts in the USA and severe deterioration of aluminum cement concrete structures in the UK have significantly changed this trend . All current reinforced concrete regulations now contain comprehensive models and recommendations regarding durability .
By Vicente Albero 1 * , David Hernández-Figueirido 1 , Marta Roig-Flores 1 , Toni Melchor-Eixea 1 , Ana Piquer 1 ; 1 Universitat Jaume I , Castellón , Spain . Email : valbero @ uji . es
Concrete coatings protect reinforced concrete structures from corrosion , acting as a physical barrier to protecting steel rebar from external erosion . Passivation also protects steel embedded in concrete from corrosion . This passivation is achieved due to the high alkalinity of the concrete mass ( pH value between 12.6 and 14 ). Current reinforced concrete regulations require minimum coatings based on the corrosive nature of the external environment . In many cases , this measure , combined with the correct concrete mix , design , placement , compaction and curing , is sufficient to protect the steel from corrosion and ensure its durability throughout the structure ’ s life . However , the durability of reinforced concrete elements may be undermined if aggressive substances penetrate the concrete ’ s pore network and the passivation layer becomes unstable . In recent decades , strategies developed to achieve better corrosion protection of steel bars can be broadly divided into two categories : those acting on concrete and those acting on steel bars . Currently , the most widely used strategy is to act on the steel bars . Stainless steel reinforcements with a chromium content of > 12 % have self-passivating properties , providing excellent performance for long-term corrosion protection . The increased use of stainless steel rebar is reflected in the publication of specific European standards , such as prEN 10370:2023 , for stainless steel bars .
The measures used to protect reinforced concrete structures from corrosion can significantly impact the bonding behaviour between steel and concrete . This bonding behaviour is a key factor in stress transfer between the two materials . The International Federation of Beton ( FIB ) Model Specifications for Concrete Structural Structures 2010 and FIB Bulletin No . 10 describe liability issues associated with certain methods of corrosion protection , such as reinforcements with epoxy coatings or the use of fibre-reinforced polymer ( FRP ) reinforcements . Most international standards ( ACI , BS ) specify a 20 % to 50 % extension of the anchorage length for epoxy-coated corrosion-resistant steel bars . On the other hand , the current discussion in the scientific literature on the bond strength of galvanized reinforcements is controversial [ 1-3 ] . Certain tests show reduced adhesion strengths , and research suggests lower initial adhesion in the early stages but comparable adhesion in the later stages of concrete [ 4 ] . In the case of galvanized steels , the decline in adhesion is commonly linked to hydrogen evolution at the contact interface , arising from the chemical reaction between the zinc coating and the fresh cement matrix of the concrete . Conversely , the adhesion of stainlesssteel reinforcements , though less explored so far , is approached from a safety standpoint in current design codes [ 5 , 6 ] .
Figure 1 . Stainless steel reinforcement REBARINOX
Alleiviaing impact of industrial fires Extensive research has been conducted on the adhesion of protected reinforcements in reinforced concrete structures under typical project conditions . Yet , considerable uncertainty arises in accidental scenarios like fires , where elevated temperatures can substantially compromise the mechanical properties of structural materials . The Model Code 2010 stands as the singular standard explicitly stating that , in the case of a fire impacting unprotected reinforced concrete structures , a reduction in adhesion can be expected proportionally to the decrease in the tensile strength of concrete at high temperatures . Regarding the accidental
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