The present paper studies the corrosion behaviour of a new lower-cost type of austenitic stainless steel (SS) with a low nickel content in alkaline-saturated calcium hydroxide solution (a simulated concrete pore (SCP) solution) with sodium chloride (0.0%, 0.4%, 1.0%, 2.0%, 3.0%, and 5.0% NaCl) and embedded in alkali-activated fly ash (AAFA) mortars manufactured using two alkaline solutions, with and without chloride additions (2% and 5%), in an environment of constant 95% relative humidity. Measurements were performed at early age curing up to 180 days of experimentation. The evolution with time of electrochemical impedance spectroscopy was studied. values obtained in SCP solution or in fly ash mortars were so high that low-nickel SS preserved its passivity, exhibiting high corrosion resistance 1. Introduction Steel reinforcements embedded in concrete are protected from corrosion by a thin oxide film formed on their surfaces and maintained by the highly alkaline environment of the surrounding concrete, usually with a pH of 12-13 . However, the presence of chlorides can lead to damaging effects on passivity and the appearance of pitting corrosion when chloride ions reach the metal/concrete interface. Chloride ions are commonly found in construction materials and may originate from the external environment, as in the case of marine environments, deicing salts and acid rain . While thermodynamic can predict whether a corrosion reaction will take place, it does not provide an indication of the rate of corrosion reactions. The reaction kinetics depends on the determinant factors such as humidity, oxygen, and alkalinity medium. These factors can speed up the corrosion process [3, 4]. Together with cathodic protection and corrosion inhibitors, stainless steel (SS) reinforcements are a reliable way to guarantee the durability of reinforced concrete structures (RCSs) in extremely aggressive environments [5, 6]. Although SS reinforcements may be the most economical solution on the long term [7, 8], the initial cost involved has so far limited their use. For this reason, new SSs, in which the nickel content (subject to considerable price fluctuations due to stock market factors) is partly replaced by other elements [9, 10], are being evaluated as possible alternatives to traditional carbon steel [11, 12]. This new low-nickel SS could mean a saving of about 15–20% compared to conventional AISI 304 SS. Low-nickel austenitic SSs exhibit attractive properties that are comparable to those of traditional austenitic SSs, such as good corrosion resistance, high
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