Hydrogen Uptake and Steel Properties Due to Electrochemical Chloride Extraction from Reinforced Concrete

Abstract

The uptake of hydrogen by steel during electrochemical chloride extraction (ECE) from reinforced concrete is monitored using novel electrochemical permeation technique. Concrete blocks were cast using two chloride (Cl - ) ion concentrations of 1.7% and 3.0% by mass of cement (batches #1 & #2) respectively, and reinforced axially with a central 15 mm plain steel square bar. Two cathodic (DC) current densities of 1.0 A/m 2 and 3.0 A/m 2 of concrete surface, were used for the ECE, with 0.1M sodium borate electrolyte solution and inert titanium anode mesh. Axial tension tests as per ASTM E8M-91 were carried out after treatment to investigate the differences in fracture loads, yield and strain to fracture of treated steel. In the ECE treatment, the hydrogen uptake of steel in the batch #1 concrete was substantially greater than those of the higher contamination (batch #2). The hydrogen permeation of batch #1 specimens with an impressed current density of 3.0 A/m 2 was about four and half times that observed at a current density of 1.0 A/m 2 . At the higher chloride content, the hydrogen uptake of the steel at 3.0 A/m 2 was about twice the level at 1.0 A/m 2 . Irrespective of the impressed current density and level of concrete contamination, the ECE specimens consistently showed about 50% reductions in tensile parameters. ECE treated specimens showed significant reductions in yield and ultimate loads, with the hydrogen effects being dependent on the applied cathodic current density and initial chloride contamination. It is thus likely that the hydrogen induced failure of steel in a candidate ECE structure will be more pronounced where there is small chloride contamination coupled with the use of high strength steel.