Assessment of Damage in Corroded and FRP Repaired Corroded Beams Using Advanced NDT Techniques

Abstract

Corrosion of steel in concrete is inevitable and is a worldwide problem which causes heavy losses to the economy and industry. Concrete due to its alkaline nature (pH gt 13.5) provides a passive protective layer of oxides around the reinforcing steel initially but when exposed to severe environmental conditions (like marine exposure) corrosion in steel bar is initiated due to depassivation of this layer. Corrosion product formed has a tendency to exert tensile pressure on surrounding concrete as rust product has volume about 6-10 times that of parent steel leading to cracking and spalling of surrounding concrete. Bond deterioration at steel concrete interface and reduction in steel area due to corrosion which ultimately reduces the load carrying capacity of Reinforced Concrete (RC) structure and can be catastrophic. In countries like India with diverse environmental condition, losses due to corrosion has been estimated USD 40 billion per year for industrial and infrastructural segments. Due to this, most of the structures need repair with 10-15 years of their construction. Therefore, it becomes very important to monitor corrosion in RC structures alongwith sustained loading so that proper timely remedial measures can be adopted before degradation leads to catastrophic failures. Numerous studies have been reported by researchers in last few decades for monitoring corrosion in RC structures like visual inspection, electrochemical, optical methods, measurement of linear polarization resistance and concrete resistivity, X-ray, gamma rays, etc. But these techniques only provide qualitative information on the presence of corrosion but do not indicate the rate or extent of corrosion. In this study, an effort has been made to monitor various stages and aspects of real time corrosion in RC structures using a judicious combination of various nondestructive monitoring tools of active Ultrasonic Guided Wave (UGW), passive Acoustic Emission (AE) technique and optical Infra-Red Thermographic (IRT) technique.