Pull-out and bond degradation of steel rebars in ECE concrete

It is demonstrated in this study that application of electrochemical chloride extraction (ECE) to reinforced concrete alters the pull-out strength and bond between the embedded high strength steel (HSS) and surrounding concrete. Concrete cubes were cast using two chloride (Cl-) ion concentrations of 1.7% and 3.0% by weight of cement respectively, and reinforced axially with a central ASTM #6 plain steel bar. Two cathodic (d.c.) current densities, 1.0 A/m(2) and 3.0 A/m(2) of concrete surface, were used for the ECE studies, with 0.1M sodium berate electrolyte solution and inert titanium anode mesh. Axial pull-out tests as per ASTM Standard Test Method C234-91a, were carried out within 24 hours of terminating treatment to investigate the differences in bond stress and bar sip behaviour. ECE treated specimens showed significant reductions in pull-out strength, with the degradation in bond being dependent on the applied cathodic current density and initial chloride contamination. At an impressed current density of 3.0 A/m(2), the 1.7% Cl- ions specimens showed about 58% loss in bond strength compared with about 44% for specimens premixed with 3.0% Cl- ion. The bond strength reduction at an impressed current density of 1.0 A/m(2) was about half the reduction at current density of 3.0 A/m(2). The loss in bond strength were based on (untreated) control specimens of each type. The alkali ion accumulations around the steel rebars were observed to follow similar trend as bond degradation. It is predicted the softening effect of the alkali (sodium and potassium) ions on the cement silicate hydrates around the steel-concrete interface will have severe effect on concrete structures reinforced with HSS irrespective of their stress state. Also, concrete structures containing steel rebars with substantial corrosion product coverage are likely to experience pronounced cathodic disbondment during ECE application and within a few days of terminating the treatment.