Acoustic emission vis a vis electrochemical techniques for corrosion assessment in RC elements

Abstract

Reinforced concrete (RC) structures have the potential to be very durable and capable of withstanding a variety of adverse environmental conditions. However, failures in the RC structures still occur due to adverse effects of external or environmental agencies. One of the main causes leading to degradation of RC structures is the corrosion of steel reinforcement. Corrosion of steel rebar in concrete is an electrochemical process and it has been widely studied using various non-destructive techniques. Half-cell potential measurement is one of the most widely used, practical and standardised nondestructive method which provides an indication of the likelihood of corrosion activity at the time of measurement. The other electrochemical methods such as linear polarisation resistance, electrochemical impedance spectroscopy etc. provide corrosion rate, but the calculations are based on certain assumptions of degree of polarization of the embedded bar. Another non-destructive technique widely used in practice is ultra-sonic pulse velocity measurement. Ultrasonic guided waves at high frequencies can be effectively used to distinguish between the loss of bar crosssectional area and changing interface conditions. However, to produce guided waves in the rebar embedded in concrete, it is necessary to attach two transducers at the ends of the rebar projected out of concrete specimens, which is not possible in actual structural element. All these techniques cannot be called truly non-destructive techniques as these methods require either electrical or physical contact with steel embedded in concrete. Thus, to overcome all these difficulties, there is a need to develop a non-destructive methodology, which will assess the corrosion of steel v embedded in RC element effectively without physical contact with the rebar. The researchers have reported that acoustic emission (AE) technique is suitable for failure monitoring of various structures and can also identify onset of corrosion without physical contact with the rebar.