In recent years, fatigue cracks in an orthotropic steel deck have been reported with increase in
traffic. These damages may cause danger to the traffic on the bridges. Therefore, detection of the cracks in
early stage is highly required. In order to scan a crack in the orthotropic steel deck from pavement surface
without removing its asphalt layer, we adopt an eddy current testing technique. This technique is based on the
principle of electromagnetic induction and suitable for this application, because the deck plate is a conductor
and simple in shape. When the technique is applied through the asphalt layer of 100mm thick, the minimum
surface-breaking crack that can be detected is 100mm long. The effectiveness of the inspection technique is
confirmed by experimental and field test results. In addition, we develop a scanning system aiming at more
efficient inspection.