AE and SIBIE techniques for NDT of crack, damage, corrosion and void in concrete: Fid-Bau Portal

AE and SIBIE techniques for NDT of crack, damage, corrosion and void in concrete

Ohtsu, M. / Shigeishi, M. / Suzuki, T. / Alver, N.

The need for estimating concrete properties other than strength has been drastically increasing. In particular, quantitative identification of defects in concrete is of significant importance for maintenance, because concrete structures are no longer maintenance-free. To this end, nondestructive testings (NDT) have been intensively studied to establish practical inspection techniques. Acoustic emission (AE) techniques have been extensively studied as NDT of concrete. At the present state of the art, cracking mechanisms inside concrete, damage degree of concrete and corrosion of reinforcement can be quantitatively evaluated. Crack kinematics is identified by the SiGMA procedure based on the moment tesor of AE source. Because kinematical information is obtained as threedimensional (3-D) locations and vectors, 3-D visualization is recently developed. New AE parameters of load ratio and calm ratio are defined for qualification of the damages. Damage qualification was experimentally conducted in reinforced concrete beams damaged due to cyclic loading. AE behavior of concrete under compression is quantitatively analyzed, applying the rate process theory. Using Loland's model of damage mechanics, a relation between AE rate and the damage parameter is correlated and implemented in a database. By quantifying intact elastic moduli of concrete from the database, relative damages of concrete in existing structures are successfully estimated. Continuous AE monitoring is useful for earlier warning of corrosion in reinforcement. Onset of corrosion in reinforcement and nucleation of corrosion cracking in concrete are readily identified. These updated results are discussed. The impact echo is developed for NDT to identify defects in concrete. Resonance frequencies are applied to estimate the presence and the depth of defects. It is, however, not easy to identify particular peak frequencies only responsible for the defects. Consequently, SIBIE (Stack Imaging of Spectral Amplitudes based on Impact-Echo) procedure is developed. The procedure is successfully applied to identify an ungrouted tendon duct of plastic sheath in a prestressed concrete (PC). Determination of surface-crack depths is also attempted.