Effects of External Confinement on Reinforcing Steel Corrosion in Concrete

This paper summarizes a study of the influence of confinement pressures on the corrosion of reinforcing steel embedded in concrete. Twelve cylindrical concrete test specimens were wrapped with varying layers of carbon fiber-reinforced polymer (CFRP) to provide passive confinement pressures as a result of the restraint of expansive corrosion. Each specimen had embedded steel bars located along the axis of the cylinder. Accelerated corrosion testing was performed to induce corrosion and generate different levels of confinement stress for the steel bar. The testing regime involved wet and dry cycles of exposure to a NaCl solution on each cylinder's top surface, as well as an imposed constant voltage between the anode and cathode steel bar segments. Nonlinear finite element models were used to relate measured circumferential CFRP strains to confinement pressures. These pressures resulted from the restraint of bar expansion and acted perpendicular to the corroding surface at the bar/concrete interface. Results showed that specimens with higher levels of confinement had lower mass loss from corrosion. The final mass loss was reduced by 36% for every 1,000 psi (6.89 MPa) of average confinement pressure generated around the steel bar during the duration of testing. Confinement also reduced the rate of corrosion, especially after the cracking of concrete. However, confinement did not significantly affect time to cracking or corrosion up to the appearance of cracks.