Progress in ultrasonic SAFT-imaging of concrete: Fid-Bau Portal

Progress in ultrasonic SAFT-imaging of concrete

Schickert, M.

Among present non-destructive methods for concrete evaluation, ultrasonic testing uses relatively short wavelengths and therefore has particular potential for detailed assessment of concrete. Especially a tomographic method like SAFT reconstruction (Synthetic Aperture Focusing Technique) is able to provide high-resolution images of concrete areas. In a publication for the 1995 NDT-CE conference entitled 'Towards SAFT-Imaging in Ultrasonic Inspection of Concrete' [1], the author introduced an implementation of the SAFT algorithm and gave initial examples of its application to concrete. The present contribution summarizes progress that has been achieved for this method since then. The described SAFT reconstruction algorithm as well as additional signal processing schemes have reached an adult state and are ready to be applied in the field. In contrast, parts of the measurement process, especially the tedious transducer coupling to the concrete, still pose problems. Conventional coupling agents do not seem to be adequate. Other methods - dry coupling or other coupling agents - are becoming available, but so far the procedures are not fully controlled. When these difficulties can be overcome, applications of practical interest can be approached. Possible applications for a first step are thickness measurement, detection and location of tendon ducts, and, in certain cases, location of reinforcement. Here SAFT reconstruction using appropriate measurement equipment is promising to be of ease use and to yield reliable, high-resolution solutions. A number of further problems such as filling of tendon ducts, crack depth measurement, and honeycombing still need principal research.