Location of Reinforcement in Structures by Different Methods of Gamma-Radiography

The quantitative measurement of kind, positions and diameters of steel reinforce ments in building constructions is a typical inspection problem in civil engineering. A classical solution is the combination of film radiography with the multi angle technique and graphical backprojection. New digital detectors reduce the exposure time and allow the application of stereo radiography and computed laminography as routine applications. The computed laminography allows fast and effectively the determination of the depth of reinforcements in concrete or masonry. A selected area of the steel re-bar structure is penetrated by gamma-rays from different angles of incidence (multi angle-technique) with a Co-60-source. Instead of a radiographic film phosphor imaging plates were used as a new digital medium for filmless radiography. A 3D-image of the measured region of interest is reconstructed from the digitised projections of a test block. The reconstruction is based on special tomosynthesis algorithms which need few projections only. Radiographic techniques were uses in completion to other techniques like radar, electromagnetic alternating field inspection to examine the structure of different buildings. Experiences of inspections of historical buildings, ancient marble structures and a bridge girder are presented where different levels of radiography were applied.