Korrosionsegenskaper hos rostfritt stål i betong med hög fukthalt. Optimalt val av stålkvalitet i betongkonstruktioner

Corrosion properties of stainless steel in concrete with high water content: optimal selection of steel grade for reinforced structures

The corrosion resistance of stainless steel in chloride-containing alkaline environments is well known. There are great technical and economic interests in using stainless steel for particularly severely exposed parts of reinforced concrete structures as well as to replace corroded carbon steel reinforcement in the outer, exposed levels with stainless steel. In certain concrete constructions in Sweden rusty reinforcement has been replaced with stainless steel during repairs. Stainless steel repair reinforcement may however constitute a risk for galvanic corrosion on the remaining carbon steel reinforcement. A recently completed investigation which was partly funded by the National Road Administration (Vägverket) showed that stainless steel in contact with carbon steel in concrete exposed in ambient atmospheric conditions during two years resulted in no significant corrosion effects from the stainless steel (4 different grades) on the carbon steel. Concerning cast-in carbon steel coupled to stainless steel in concrete at high humidity or immersed in water, however, the absence of galvanic effects is not assured. It is well known that if carbon steel and stainless steel are electrically coupled to each other and immersed in a chloride-containing aqueous solution, the carbon steel will undergo severe galvanic corrosion. That no significant galvanic effects have been found in concrete at ambient humidity levels may to some part be due to the low conductivity in partly air-filled concrete. The galvanic corrosion can thus be larger in concrete with a high water content (low resistance), such as may occur in road environments due to rain, melting snow etc., and for e g bridge columns in water. The project will include long-term field and laboratory exposures of stainless steels coupled to carbon steel and cast in concrete blocks. For the field exposures realistic environments corresponding to severe use conditions will be chosen, e. g. a highly corrosive road environment with respect to chlorides and period of wetness.The results from the investigations will be included in and complement the recommendations that are in preparation concerning an optimal selection of stainless steel for reinforcement in new constructions as well as repairs.