Ultrasonic Guided Wave and Acoustic Emission Techniques for monitoring corrosion in Reinforced Concrete Structures

Abstract

Corrosion of reinforcement is one of the principal causes of premature failure of Reinforced Concrete (RC) structures. In India, the annual loss due to corrosion has been estimated about 4% of the country s gross domestic product (GDP) i.e., about USD 40 billion in a year in both infrastructure and industry segments. Exposure to extreme environments and the continuous ingress of chlorides in concrete from various sources neutralises the protective passive layer of concrete which is alkaline with a pH ranging from 12 to 13. The presence of moisture and oxygen leads to the formation of oxides and the initiation of reinforcement corrosion takes place. Corrosion of reinforcement in concrete affects the durability of the RC structures in two ways: the formation of rust products with larger volume than steel leads to spalling and the cracking of the concrete cover; and the area of cross-section of the steel bars reduces drastically due to dissolution of the steel leading to pit formation and hence, loss in the tensile strength and load carrying capacity of the structure. Therefore, an early prognosis and diagnosis of corrosion-induced damage in RC structures could facilitate the engineers to adopt correct repair measures. A large variety of non-destructive techniques have been reported by researchers worldwide for detecting corrosion-induced damage in RC structures like visual inspection, electrochemical, Optical methods, PZT and piezo ceramic patches etc. but they suffer from practical applications owing to large civil infrastructure. Recently, the advent of wave propagation technologies for damage detection in RC structures have given a new dimension to damage monitoring capabilities. In this work, an integrated approach using active Ultrasonic Guided Wave (UGW) and passive Acoustic Emission (AE) technique for corrosion monitoring in RC structures has been attempted.