Nondestructive measurement of concrete cover thickness, state of the art for the development of a new equipment

In recent years, there is a conclusive evidence that corrosion of reinforcing steel bars in concrete structures can be prevented if the concrete cover is thick enough. Depending on the steel bar diameter and the environmental conditions, national standards ask for minimum cover thickness which is, in average, larger than 30 mm. Most of the equipment available in the market use eddy current or magnetic technique for the evaluation of concrete thickness. The influence of the differences in steel bar diameter and quality are ignored during the concrete thickness evaluation using the commercial equipment resulting in a mean square deviation of 30% as compared to the real cover thickness. This paper discusses a new magnetic technique and the state of the equipment development for measuring the concrete cover thickness more accurately.