Combined application of an optical sensor and a common non-destructive instrument for corrosion monitoring in reinforced concrete members

Abstract

The reliable monitoring of the progression or extent of pitting-type corrosion in reinforced concrete members requires great effort due to non-uniformity. This paper presents a new approach for measuring the progression and extent of pitting-type (non-uniform) corrosion in reinforced concrete members by combining both non-destructive testing with optical fibre sensing results. Accelerated corrosion on the reinforcement (rebar) of the specimen was produced artificially using an alternate wetting and drying process in sodium chloride solution with 7.5% and 10% concentrations. The multimode optical fibre patch cords were attached to the reinforcement in three different arrangements in a single specimen (normal optical patch cord and loose and firm microbend patch cords). Intensity loss in a propagating light travelling inside an optical fibre takes place due to the development of pressure from surrounding concrete on the fibre from rust formation (corrosion). The study also describes the effect of corrosion in half-cell potentiometer, chloride ion resistivity and indirect pulse velocity readings obtained from the specimen. A later study found that the use of an optical microbend sensor is an effective alternate method for determining the starting time of initial depassivation in the reinforcement and validates it using half-cell potentiometer values. The study also developed models to predict overall mass loss in the rebar due to corrosion using combined non-destructive testing methods.