Corrosion of rebar in concrete. Part IV. On the theoretical basis of the chloride threshold

A theory is developed for calculating the chloride threshold (CT) from the Point Defect Model (PDM). CT is defined as the ratio [Cl<sup>-</sup>]/[OH<sup>-</sup>] at which the passivity breakdown voltage (E<sub>b</sub>) equals the corrosion potential, ECP. CT is sensitive to the T, ECP, pH, and E<sub>b</sub>, because all four appear in the exponent X in CT = 10<sup>X</sup>. Small uncertainties in these parameters translate into a large uncertainty in CT, emphasizing the need for accurate T, ECP, pH, and E<sub>b</sub> data. We demonstrate the theory by successfully calculating CT using data for selected systems.