ACOUSTIC EMISSION & NDT SCIENTIFIC PUBLICATIONS

 

Damage Level Evaluation and Characterization by Acoustic Emission and Acousto-Ultrasonics in Concrete Under Compressive Loads

 

15th World Conference on Non-Destructive Testing, Rome, Italy, 15-21 October, 2000
Apostolos Tsimogiannis, Barbara Georgali. Dr. Athanasios Anastasopoulos

 

The level of damage sustained by concrete structures is an area with increasing interest. At present monitoring damage in concrete is performed mainly by microscopic analysis which is a destructive method and requires a significant time interval to produce results and by simple compressive strength tests which also requires sample removal. Localized inspection by Non Destructive Testing (NDT) methods encounters a number of difficulties in concrete structures due to the nature of the material and can thus be applied only in a limited number of cases and usually when macro-cracking or other form of damage exists. Acoustic Emission (AE) has been used successfully in monitoring damage accumulation, crack growth etc. in large concrete structures when loads can be applied (bridges, piers etc.). Location of damage is possible along with other parameters (crack growth, orientation etc.). In structures where load application is difficult (e.g. buildings) the method is not used. To monitor damage on buildings Acousto-Ultrasonic (AU) is suggested as a technique. AU has been used to quantify macro-cracking in concrete structures. In the present work mortar cement specimens are being monitored by AE and AU during compressive tests to failure. AE is used to confirm microscopic damage in the specimens under loading. The state of the concrete is simultaneously monitored by AU and an attempt to correlate damage level as given by AU with AE measurements is made. The attempt is to characterize damage at early stages and produce an indication of approaching failure of the material. An attempt is also made to correlate AU/AE parameters to the mechanisms producing the microscopic damage in the specimens at early stages using microscopy findings for various times in the specimensí lives. The results show clear indications that AU can detect sustained damage at the microscopic level in concrete and can give early indications of oncoming failure. In addition AU provides a means to monitor and characterize events at the microscopic level of concrete in real-time.