Steel bar corrosion monitoring with long-period fiber grating sensors coated with nano iron/silica particles and polyurethane

In this article, a recently proposed long-period fiber grating sensor coated with a thin layer of polyurethane and nano iron/silica particles is further developed and applied to monitor the corrosion process of deformed steel bars. Once calibrated, one coated long-period fiber grating sensor and one uncoated long-period fiber grating sensor for environmental compensation were attached to each of three steel bar samples that were tested in 3.5 wt% NaCl solution for 512h. The resonant wavelength in long-period fiber grating spectra increased exponentially with immersion time due to corrosion of iron particles and thus reduction in coating thickness. The mass loss rate of steel bar #1 at the completion of corrosion tests (512h of corrosion time) was correlated with that of sparse iron particles on long-period fiber grating sensor #1 after 130.5h of immersion. The corrosion rates of long-period fiber grating sensors #2 and #3 were evaluated at 130.5h and then used as a prediction of the corrosion rates of steel bars #2 and #3. The predicted corrosion rates by the long-period fiber grating sensors #2 and #3 were finally compared with those by potentiodynamic tests. The maximum mass loss prediction error by the long-period fiber grating sensors #2 and #3 is 26%. The coefficients of variation of three corrosion rate measurements are 0.049 by the long-period fiber grating sensors and 0.115 by the potentiodynamic tests, indicating more consistent and reliable measurements with the proposed technology.