To go beyond current electromagnetic nondestructive evaluation (NDE) methods for reinforcing bar (rebar) corrosion we are exploring unique magnetic or electric spectral features and whether these might be prominent enough at the concrete cover depth to leverage in order to quantify it in concrete at early stages. We measured the dielectric and magnetic responses of concrete and iron-bearing-oxide corrosion specimens as S-parameters from 45 MHz to 12 GHz. To quantify cover layer propagation we cut and carefully fit samples from residential concrete into three different waveguides and in one case poured and cured a freshly mixed cement-sand mixture in S-band waveguide to determine permittivity and propagation loss as a function of temperature and humidity. Our measurements make it clear that the granite rock added to fill about half the volume of modern concrete also reduces its electromagnetic propagation loss by roughly this percentage. We packed ground corrosion samples and commercially available iron-oxide powders (hematite, maghemite, goethite, and magnetite) into 7 mm airline to determine prominent spectral features which could identify/quantify rebar corrosion. Magnetite shows prominent magnetic permeability and loss features, which may be useful for corrosion detection. As a prelude to future measurements, we also performed more casual reflection (S11) measurements at rebar corrosion surfaces with an open coaxial probe place on many such sites and sweeping a range from 45 MHz up to 50 GHz. The bridge engineer will not find a punch-line here, but it is a strong materials basis for new methods development.
Citation: Journal of Research (NIST JRES) -
NIST Pub Series: Journal of Research (NIST JRES)
Pub Type: NIST Pubs