Leaching-induced corrosion of the reinforcing steel in water-bearing separating cracks

Leaching-induced corrosion of the reinforcing steel in water-bearing separating cracks When water flows through separating cracks or construction joints, the cement paste leaches out, and alkalinity is reduced. As with carbonation, this decrease in pH leads to the loss of the passive layer, which is limited to the directly adjacent area. The progress of corrosion may depend on the water exchange rate. This presented study investigates the influence of the water pressure level on test specimens with crack widths between 0.20 and 0.25 mm (mean values) on the onset of depassivation and the corrosion rate. The test specimens were exposed to demineralised water at a hydrostatic pressure of 0.04 bar, 0.20 bar or 1.00 bar and monitored for corrosion. A few days after the start of exposure, high macroelement currents flow in all test specimens. Later, due to self-healing, the flow stops at 0.04 bar, and the macroelement currents decrease significantly. In contrast, the reduced but steady flow at 0.20 and 1.00 bar leads to a continuous corrosion progression. While a (planned) longer interruption of the water supply results in repassivation of the steel, renewed pressurisation significantly increases both the flow and corrosion rates. The leaching manifests in an increase in the pH of the effluent water and a reduced calcium concentration in the crack area.