Initial-corrosion condition behavior of the Cr and Al alloy steel bars in coral concrete for marine construction

Abstract

Abstract To improve the corrosion resistance of the steel matrix, 1% and 3% Cr and 1% Al are added to ordinary carbon steel for the design of a corrosion-resistant alloying composition. And based on the principle of electrochemical tests, a method for determining the depassivation of Cr and Al alloy steel bars in coral aggregate concrete (CAC) is established. The equivalent circuit model was used based on the electrochemical impedance spectroscopy (EIS) results to characterise the corrosion behaviour of the Cr and Al alloy steel bars and determine their corrosion resistance and the protective effect of the steel bar passivation film. The corrosion resistance of the Cr1 reinforcement to chloride increases by 37.67%, that of the CrAl reinforcement increases by 64.08%, and that of the Cr3 reinforcement increases by 171.82% with respect to that of the HPB 400\u202fbar. The polarisation curves of the alloy steel bars with different Cr and Al contents in CAC were recorded by linear polarisation resistance (LPR), and the time variations of the corrosion potential and corrosion current in the low-alloy steel bars containing Cr and Al were analysed. In addition, the free chloride ion concentration and pH value of the CAC were measured while the Cr and Al alloy steel bars were rusting. The chloride threshold values (% by weight of concrete) of the HPB 400, Cr1, CrAl, and Cr3 steel bars are 0.515%, 0.718%, 0.950%, and 1.084%, and the chloride thresholds (Cl−/OH− ratio) are 0.288, 0.382, 0.502, and 0.693, respectively. Initial-corrosion condition behavior of the Cr and Al alloy steel bars in CAC was obtained. There is considerable scientific value and application significance attainable from the examination of the corrosion mechanism and behavior of corrosion-resistant steel bars in a harsh marine environment.