Executive Summary : | Corrosion leads to premature deterioration and often a dramatic reduction in the service life and increase in life-cycle maintenance costs of reinforced concrete (RC) structures. Non-destructive detection of incipient corrosion has long been an impending task. In this project, investigators propose two complementary low cost sensing platforms based on principles of eddy current and ultrasonics to identify the mechanism of corrosion process, which involves corrosion initiation, progression, rebar diameter reduction and debonding. The non-invasive eddy current based system will deploy a pair of coils to induce and sense pulsed eddy currents in the rebars. The sensed current is phase shifted with respect to the transmitter by an amount proportional to the conductivity of the metal surface, and is measured accurately using a phase sensitive detection circuit to estimate the severity of corrosion. The amplitude of the receiver signal could also be exploited to estimate rebar depth and diameter. On the other hand, the ultrasonic system comprised of a low cost portable transceiver would act as an embedded smart sensing system using water-proof ultrasonic piezoelectric wafer transducers (PWTs) at concrete-steel interface for real-time monitoring and assessment of corrosion growth. Since the proposed technique relies on high frequency ultrasonic guided waves that travel long distances, a large area can be interrogated using a few PWTs to identify the location and severity of corrosion growth. Accelerated corrosion testing will be performed through an electro-chemical reaction by exposing concrete beams with varying rebar diameters to chloride environment and using impressed current method. The two complementary systems would be equipped with damage diagnosis and imaging software based on machine learning using MATLAB interface and Digital Signal Processing (DSP). This technology will help estimate the remaining service life of RC structures and aid maintenance strategy decisions. |