Investigation of Effectiveness of Various Corrosion Protection Methods By Ultrasonic Guided Waves and Acoustic Emission Techniques

Abstract

Corrosion of reinforcement in RC structures is like a 'Cancer' which spreads , if not intervened at the right time. It is one of the major challenges faced by structural engineers. World-wide, billions of dollar are wasted on structural maintenance because of undetected corrosion. It results in the cracking and spalling of concrete and loss of cross-section in the form of pitting in reinforcement and can ultimately lead to catastrophic failure of structures. Therefore, non- destructive monitoring of corrosion in reinforcement is very essential. In this research, monitoring of corrosion in RC structures using a combination of elastic wave techniques of Acoustic Emission and Ultrasonic Guided Wave is employed. The efficacy of corrosion impediment by various corrosion prevention methods using epoxy and paint coating on rebar and corrosion inhibitor admixed with concrete is evaluated. Four concrete beam specimens of dimensions 150mm X 150mm X 700mm with MS bar of 1m length and 25mm diameter in the center of cross-section were cast. 1st beam specimen was control specimen, 2nd beam specimen had steel bar coated with epoxy layer, 3rd beam specimen had a steel bar coated with paint and 4th beam specimen was prepared using corrosion inhibitor as an admixture in concrete. All the beam specimens were subjected to accelerated corrosion exposure for 30 days. Ultrasonic monitoring was done after every 24 hours for the entire duration of corrosion exposure. A low frequency mode L(0,1) at 0.1MHz and a high frequency mode L(0,7) at 1MHz were used for Ultrasonic Guided Waves measurements. For Acoustic Emission monitoring 4 AE sensors were mounted on the surface of concrete which collected AE activity during the entire duration of the corrosion exposure. It was found that both the techniques are effective to different extents in picking up corrosion effects in steel and concrete. It was also reported that the specimens treated with epoxy and paint did not undergo any corrosion activity picked up by both UGW and AE even under the accelerated corrosion conditions. The specimen treated with corrosion inhibitor showed a delay in delamination and pitting in comparison to control beam which was easily picked up by the change in signals obtained using UGW monitoring and a delay in the corrosion onset and cracking was also picked up by AE monitoring.