An alternative method to measure corrosion rate of reinforced concrete structures

A new probe, which does not use a confinement ring, has been developed to assess the corrosion state of reinforced concrete structures. Galvanostatic polarization is performed and the rebar corrosion potential, concrete cover resistivity and rebar corrosion rate are evaluated using an iterative calculation algorithm. The surface linear polarization resistance (RP,s = ΔEP/jPI) of the rebar/concrete interface is calculated by converting the potential measured at the surface ΔEP,surf into the rebar polarization ΔEP and the current density at the point of interest (PI) jPI using 3D numerical simulations. The calculation involves three geometrical parameters that modify the current and potential distribution in the concrete: the rebar spacing s, the concrete cover c, and the rebar diameter D. Concrete cover resistivity is calculated using the instantaneous ohmic drop measured at the beginning of the galvanostatic polarization and the rebar corrosion rate is calculated using the steady-state potential. As the rebar corrosion rate also modifies the potential distribution in concrete, an iterative methodology was developed, using different supposed corrosion rates. Finally, the probe and associated methodology were used to evaluate the corrosion state of eight concrete slabs. Half of them were prepared with chloride in order to initiate corrosion. Four slabs were stored outdoors, two indoors in an ordinary laboratory environment and two indoors in a 50% CO2 gas chamber. The three corrosion parameters evaluated (corrosion potential, concrete cover resistivity and rebar corrosion rate) were in good agreement with the composition of the slabs and their curing conditions.