NDE of distributed cracking in concrete

An experimental program was conducted to evaluate ultrasonic techniques for evaluating distributed cracking in concrete structures. Distributed cracking here refers primarily to microcracking and other high porosity zones which typically precede large scale cracking. Several mechanisms were identified as primary causes for distributed cracking in concrete. These mechanisms include freeze-thaw, salt scaling, and mechanical stresses. A series of specimens were cast and subjected to these effects. Immersion scanning techniques were used to measure ultrasonic properties (pulse velocity and peak-to-peak amplitude). The changes in ultrasonic properties with increasing degrees of damage were compared to corresponding changes in material properties. Amplitude attenuation was found to be a much more sensitive indicator of damage than pulse velocity. The results of the experiments show that NDE techniques can be developed which use relative ultrasonic attenuation measurements as an indicator of damage and structural integrity in field structures.