Permittivity analysis of weathered concrete in a bridge based on open-ended probe and impedance measurements

Abstract

Pathologies like corrosion of rebars or alkali aggregate reactions in a reinforced concrete (RC) bridge are usually accompanied by the existence of aqueous pore solutions with a high concentration of ions. The distribution of aqueous solutions in the concrete is inhomogeneous and depends on the RC’s location in the bridge and complex climate factors. Frequency-dependent complex permittivity is sensitive to aqueous pore solutions because the high conductivity caused by charge carriers can result in a large imaginary part of the permittivity, much higher than that caused by water. In this study, we used a non-destructive open-ended probe to measure the complex permittivity of the RC in a bridge’s pillar with different levels of pathologies. By measuring the impedance of core samples with various controlled water volumetric fractions in the laboratory, the water effect on the evolution of the loss tangent (the ratio between the imaginary part of the permittivity and the real part) can be calibrated. Comparing the loss tangent in the bridge with that of the core samples treated by water, we can map the areas with a high density of aqueous pore solution and cracks, and estimate the unhealthy area with partial damage in the pillar by an effective and non-destructive diagnosis.