NDT honeycomb detection in concrete with ultrasound

Honeycombing can be detected using ultrasonic pulse echo technology. The ease with which it can be detected and the strength of the echoes received depend on how loose the honeycombing is.

Honeycombing that contains more air is easier to detect. It results in stronger echoes. Dense honeycombing, on the other hand, is harder to detect but can also be considered less of a structural issue. 



Loose honeycombing

The first schematic image shows a test block with a V-shaped back wall and honeycombing in its upper left corner.

On a scan performed on such a test block, the thickness variation of the back wall can be easily identified. The honeycombing is loose in this case, and can be clearly seen at a depth of 13 cm (marked by the cross hairs on the second picture).

Dense honeycombing

In comparison, the second schematic image illustrates a test block of 200 mm thickness. It has an area of densely packed honeycombing.

The only indication on the scan that there is some kind of defect is the deformation of the back wall echo. This 'bulge' originates from the longer sound path of the ultrasonic signal path caused by the object. However, the object itself cannot be seen.