Steel corrosion resistance in model solutions, containing waste materials

This work reports on the corrosion resistance of low-carbon steel in alkaline model solutions, i.e. “red mud” (RM) containing extracts of Ordinary Portland Cement (OPC) and Blast Furnace Slag (BFS) cement. The objective was to define the steel electrochemical behavior and the properties (morphology and composition) of the product layer that forms on the steel surface within treatment in chloride-free and chloride-containing model solutions. The motivation for this research is related to several aspects, mainly to exploring the possibility for achieving superior corrosion performance of steel in cement-based systems by using (combination of) waste materials.The study reveals that RM has a distinctive positive effect on the corrosion performance of steel, especially in chloride containing environment. The presence of RM in both OPC and BFS solutions (with and without NaCl) favors steel passivation and results in an increased corrosion resistance. The positive effect of RM is especially pronounced for steel, exposed to BFS solutions. The observed behavior is attributed to the presence of Fe2O3 and Al2O3 (from RM and BFS). The presence of Fe3+ stabilizes the passive layer. Additionally, the adhered red mud particles act as adsorption sites for Ca2+, resulting in a product layer with higher corrosion resistance. Further, the RM particles with regard to their Al2O3 content enhance steel passivity and increase the chloride threshold for corrosion initiation and/or propagation.

► The presence of red mud in simulated concrete pore water environment favors steel passivation.
► A distinctive positive effect of red mud was observed for Blast Furnace Slag-containing medium.
► Altered redox activity (due to the presence of Fe3+) and Ca-substituted product layers lead to enhanced corrosion resistance.