A series of investigations were carried out on a precast concrete duct in Tarbes, France, which displayed damage patterns. The aim of the study was to rank 55 similar pipe segments in order to determine severity of the damage. The methods used were electrical resistivity measurement, passive infrared thermography and the capacitor method. The fi rst step was to clarify the accuracy of the site measurements of the various techniques in a real situation. All methods allowed water content rate variations and cracks to be distinguished on the surface of concrete. Statistical analysis of the data helped the interpretation of measurements to develop a hypothesis. This original work, analysing several nondestructive test techniques, then combining results, led to establishing a link between damage and moisture. The experimental results have been used to try to quantify the value of the surface moisture. This appears to be the most important physical factor influencing measurements as well as being a way to assess damage.