NONDESTRUCTIVE TESTING OF REINFORCED AND PRE-STRESSED CONCRETE STRUCTURES

The integrity of internal steel components, whether they be in the form of reinforcing bar mesh, pre-tensioned tendons or post-tensioned cables encased within ducts, is a major factor in determining the useful life of structures built from reinforced and pre-stressed concrete. This article reviews the nondestructive techniques that have been or are being developed which provide information relating to the condition of these steel members, either through direct or indirect measurement. It focuses on the research that has been conducted on true nondestructive methods, giving only brief consideration to electrochemical techniques such as potential mapping, which require at least one-contact point with the steel, and hence removal of some concrete. Testing methods given special attention are those based on the principles of ultrasound, impact echo, acoustic emission, radar and microwave, X-ray and gamma radiography, AC and DC magnetic fields, electrical and optical time domain reflectometry and thermography. The article notes that testing using a particular method can be performed by exploiting different effects, for example ultrasound methods may be based on pulse-echo analysis or frequency response. Hence each section is classified into sub-sections detailing the various processing algorithms employed. Relevant theory, together with key formulae are also included for each technique.