2D and 3D electrical tomography: Corrosion diagnosis of reinforced cement-based materials – EL-TORO

EL-TORO aims at developing a novel reliable and modular multi-electrodes device for the non-destructive monitoring and diagnosis of Reinforced Cement-based (RC) structures. The device will provide 2D/3D images of both the electrical resistivity of the cement-based materials (?, in O.m) and the polarization resistance of the steel-rebar (Rp, in O) distributions of the probed volume. The innovation consists in integrating the physics of the “Butler-Volmer equation” into an existing open-source Direct Current (DC) resistivity inversion code to take into account the electrochemical properties of the rebar at the steel-concrete interface in the forward model. Indeed, the multi-electrode device will provide 2D/3D “apparent” measurements of voltages, in time-domain, sensitive to increasing investigation depths from the concrete surface. The inversion of the “apparent” measurements will provide 2D/3D images of ? and Rp.

The ability of the software package to reproduce corrosion rates will be tested, by using simulated data based on different scenarii of degraded RC structures provided by COMSOL Multiphysics®. Then, combined multistep and multiscale approaches are proposed to gain insights into the role of the main influencing factors in the assessment of corrosion and ‘decipher’ the impact of each environmental parameter on the measured signals. Performances and reliability of the developed methodology will be optimized and verified in laboratory, on a set of decimetric RC samples, under well-controlled conditions of T°, RH and pCO2 and on another set, submitted to controlled artificial tidal conditions. The in situ robustness of the device will be investigated, on sub-metric RC samples and actual structures submitted to natural tidal conditions (Tower Saint Nicolas, the historic tidal pool site of La Rochelle).

The strength of EL-TORO project is based on the coherent multidisciplinary partnership covering a large spectrum of specific disciplines of the application domain. IRIS Instruments, which is the industrial partner, has a strong background in designing, manufacturing and selling of geophysical equipment, monitoring geo-materials and inversion programming. BRGM and LaSIE benefit from electrochemists specialized in corrosion sensing and monitoring, geochemists and mineralogists specialized in the elaboration and characterization of RC material, engineer specialized in numerical simulation and, genie civil engineers specialized in investigating and modeling transfers in porous media.

The final device developed in EL-TORO will be an integrated and flexible system for the mapping of the spatial distribution of anomalies and for quantitative corrosion diagnosis of actual RC infrastructures . The level of the technology maturity, at the end of the project, is expected to be TRL5 (Technology Readiness Level: component validation in relevant environment). The EL-TORO project, thus, opens up new economic perspectives for IRIS Instruments that will commercialize the developed device. The academic partners will have the opportunity to pursue their research in this topic with a constant resourcing from the market.