Concrete Slab NDT

[SteelPE]

I have a project that I am currently working on with a client that requires the client to install a few pipes through an existing slab. At this point, I am not overly concerned with the penetrations as they are somewhat small (mostly 2” dia holes with a few 3” dia and on 4” dia hole). These holes will be scattered throughout the slab in various areas.

The GC has some flexibility as to where these holes can go and we both agree that it will not be wise to core through any existing reinforcing. I am looking for recommendations as to what type of NDT should be done to determine the existing slab reinforcing. As of right now, I am focusing on GPR. Will GPR be enough to provide location and depth of reinforcing in an existing slab or are there other tests that will need to be performed in order to answer these questions?

 

[WesternJeb]

We cut a 2' diameter hole in a 14" structural slab using GPR to locate reinforcement and find a beam hidden in the slab. The contractor we hired said they could get a rough depth, but the reinforcement only showed up once so they were assuming (correctly) that the rebar was directly in line with each other. The scan was dirt cheap (around $1,000) and the benefit of it was unmatched.

 

[structSU10]

GPR is likely the right NDT for this. The top bar, if it exists, will tend to cast a 'shadow' that could obfuscate what may be below. Depending on the slab thickness and density of the rebar you may not get a view of it at all, but I would be surprised if that were the case. You could scan both top and bottom of slab if it is unclear, but overhead scanning may be a pain.

Generally the GPR technician will mark the floor where the bars appear to be, and I have seen them use different colors to denote top and bottom bars.

 

[GC_Hopi]

FYI, my experience is that the maximum scan is ~10 inches for GPR and GPR is state of the art for locating reinforcement. Like EIT stated you would hire a third party specialty company, either material testing or specialty demo/mechanical contractor, for a fee and they have the higher end equipment.