A study on ultrasonic echo tomography for non-destructive evaluation of hardened cementitious concrete

摘要

Ultrasonic Echo Tomography (UET) technology has been used as a tool to assess the condition of hardened cementitious concrete by detecting possible subsurface anomalies such as honeycombing, delamination, and air-pocket. In this study, the performance of UET was evaluated in a laboratory study and in three field case studies. In the laboratory, a concrete slab specimen was prepared with manmade honeycombing, delamination, and voids. Steel reinforcing bars with different diameters and a nonmetallic pipe were pre-embedded in the concrete slab. The three field case studies involved evaluating structural beams, a reinforced concrete floor slab, and some reinforced concrete walls constructed with normal-weight concrete. Based on the limited information obtained in this study, it was determined that significant honeycombing, cracks, delamination, and backside of the concrete member formed interfaces with the concrete matrix that could significantly reflect ultrasonic waves. These subsurface objects were clearly imaged by UET at a greater depth from the concrete surface of scanning. Steel reinforcing bars and cluster of small voids formed interfaces with the concrete matrix that could reflect a small amount of ultrasonic wave. These subsurface objects could not be imaged due to attenuation if they were located too deep from the concrete surface. For subsurface objects located close to the concrete surface in a porous concrete matrix, they might not be imaged due to the increased attenuation of ultrasonic waves. A gap in the backside reflection could indicate the presence of subsurface objects that could not be observed in a UET image. Needs for future research were proposed in this study.