Proper maintenance of concrete structures requires close inspection and accurate understanding of the current condition of the structures. Visual observation is the most common means of inspection. However, some suitable non-destructive inspection will be needed in addition to visual inspection, especially for evaluating important factors which are deeply related to safety or durability of structures. This paper describes various non-destructive testing techniques recently put in use in the field of road or railway bridges and provides inspection methods using these techniques applicable to concrete quality evaluation, detection of cracks, voids, spalling or other defects in concrete, and evaluation of sheath grouting which is specifically important for prestressed concrete structures.

Keywords: Concrete, Inspection, Visual observation, Durability, Non-destructive testing.