ULTRASONIC INVESTIGATION OF CONCRETE WITH DISTRIBUTED DAMAGE

An experimental program was conducted to evaluate ultrasonic technique s for measuring distributed cracking in concrete structures. Distribut ed cracking here refers primarily to microcracking and other high poro sity regions which generally precede large cracks. An investigation of distributed cracking yields information on weaknesses in the material which may ultimately lend to major-cracking and failure, but also can be used to evaluate distress mechanisms which do not necessarily resu lt inlarge cracks Distributed cracking in concrete was induced by free ze-thaw cycling and salt-scaling. Ultrasonic tests were used to measur e changes in attenuation. pulse velocity and peak frequency of the ult rasonic waves due to the distributed damage. The ultrasonic measuremen ts were correlated with damage observed using optical microscopy. It w as found that ultrasonic pulse velocity was not very sensitive to chan ges caused by distributed microcracking. The change in signal amplitud e (a measure of ultrasonic attention) on the other hand was quite sens itive to changes caused by microcracking, although the measurements sh owed considerable scatter. The peak frequency of the ultrasonic signal was also quite sensitive to the condition of the concrete. These resu lts must be considered in the development field rests for evaluation o f concrete structures.