Cracking in concrete

[Zambo]

I am working on a post-tensioned elevated road. At the point where there is a junction between a ramp and the main line we have cracking at the intersection. We need to determine if this is surface cracking or whether there is a structural failure around the tendons. We are carrying out an investigation into the sufficiency of the anti-spalling rebar, but in the meantime we wish to detect the depth of the cracks. Is ultrasonic NDT testing appropriate for this, the concrete is heavily reinforced with 10 No. 19 strand tendons and about 1.0m thick.

Zambo

 

[Zambo]

Just had a visit to site by a testing company. They recommend X-ray (although I think they may mean radiography) but will make a proposal later in the week. Any thoughts from anyone on the best NDT technique?

Zambo

 

[Ron]

If your testing company recommended radiography for this application, get another testing company.

You are looking for the depth of cracking and the characterization of the cracks. Radiography done parallel to such cracks will tell nothing, plus since the thickness is noted as 1m, conventional radiography will not work. Also, you must have access to both sides of the concrete to do radiography and such access might not be available if this is a transition ramp on fill.

There is not a convenient nondestuctive method that will work well for this application. You need mostly to look at the pattern of the cracking and surmise the source from the pattern. Crack width and orientation will tell you a lot. Crack depth is difficult to discern, though often the depth can be estimated from the location and width of cracks.