The use of corrosion resistant steel reinforcement in chlorides contaminated concrete

摘要

From experiences and many examples from real life it is obvious that the problem of corrosion in reinforced concrete structures is still being unsolved. Despite numerous anticorrosion protection methods that are based on prevention of electrochemical processes (i.e. cathodic protection, corrosion inhibitors, etc.), the use of stainless steel reinforcement is considered as one of the best methods for protection of reinforced structures exposed to aggressive environments.The main problems concerning the use of stainless steel reinforcement in concrete structures are: 1) insufficient knowledge about basic corrosion mechanisms of stainless steel in concrete and lack of experiences from real life implementation; 2) much higher price of stainless steel reinforcements (especially high-Ni alloyed steels), compared to carbon i.e. black steel reinforcement.rnTo address both of these problems, the corrosion resistance of 6 different types of corrosion resistant steel reinforcements (ferritic TOP12 – 1.4003, austenitic low-Ni 204Cu – 1.4597, austenitic AISI 304 – 1.4301 and 304L – 1.4306, duplex SAE/UNS S3 2205 – 1.4462 and UGIGRIP 4362 – 1.4362) were tested in simulated concrete pore solution (carbonated and non-carbonated, with different additions of Cl~-) and embedded in small laboratory concrete specimens (cyclically wetted with NaCl solution). Next to laboratory results, concrete columns were prepared and exposed to real marine environment. During 4-year exposure of columns at the coastal area, frequent measurements were performed on embedded reinforced steel: galvanostatic pulse measurements, Electrical Resistance (ER) probes measurements and Electro-chemical Noise sensors (EN measurements). After 4 years, concrete columns were transported to laboratory, where final (visual, microscopy, CT, etc.) inspection of embedded steel, different probes and concrete itself was performed. Results of non-destructive measurements were compared to final (destructive) examination.rnThe preliminary results show that ferritic stainless steel (TOP12) does not seem to be more suitable for the use in chloride contaminated environment than black steel. On the contrary, low-Ni austenitic stainless steel (204Cu) show relatively good corrosion resistance when compared to more expensive austenitic AISI 304, 304L and both duplex steels (duplex SAE/UNS S3 2205 and UGIGRIP 4362 – 1.436).rnLessons learned from first test site were used to establish new test site in marine environment, where carbon steel reinforcement, austenitic low-Ni (204Cu – 1.4597) and austenitic (AISI 304 – 1.4301) stainless steel reinforcements were embedded in two different types of concrete. Beside steel reinforcement, the exposed columns have embedded sensors for EN measurements and improved ER probes for continuous data acquisition. The purpose of the new test site is to compare different options for non-destructive detection of corrosion in real concrete structures and to establish new smart corrosion system.