Low frequency - high tech
The Ultrasonic Shear-wave Tomography (UST) technique (commonly known as “MIRA”) is a low frequency (20 to 100 kHz) multifunctional phased array ultrasonic system engineered to detect and evaluate internal reinforced concrete defects such as honeycombs or voids. Shear-wave ultrasonic testing represents one of the most advanced techniques available in nondestructive testing (NDT) of concrete, especially for large structures such as bridge piers or foundations.
Utilizing pulse-echo technique, ultrasonic MIRA testing requires only one accessible side, although testing from two opposite sides is recommended whenever possible to improve the accuracy of results. The penetration depth from one side of the concrete element is on the order of 2 to 5 ft (some researchers reported even deeper penetration capacity), depending on the amount of reinforcing steel, concrete density and other factors. Test results are presented in graphical format and 3-D slice section views which allow the depth of the anomaly to be approximated.
The minimum detectable sizes of defects using shear-wave ultrasonic testing depend on the depth of the defect, amount and depth of reinforcement, etc. Typically, the deeper the defect in the concrete, the larger the defect needs to be in order to be detected. The resolution is higher for structures with less reinforcement. Ultrasonic MIRA testing has been successfully used to detect a 3 inch hole 4 feet deep in concrete with mild reinforcing steel near the exposed surface. Like other NDT techniques, after testing is complete, truth verification using limited coring or drilling is recommended to characterize the type of defect as well as improve the level of confidence of the interpreted test results. Experience consultants in NDT technology at CTLGroup produce the most accurate results possible and provide expert interpretation of these results.