Diagnosing slab heave with x-rays

X-Raying Concrete

Knowing what is inside an existing concrete slab can be a great benefit.

When doing a slab heave investigation, knowing the:

  • thickness of the concrete slab
  • the thickness and location of slab reinforcement
  • the depth of internal slab thickenings (if any)
  • the reinforcement in slab thickenings

can help you assess the compliance of the construction with the design drawings.

You might be tempted to engage the services of a concrete x-ray company. If you do, the biggest issue is reliability of the results and assessing the results.

Establish a Benchmark

Do not use the results of an x-ray survey in court without establishing a benchmark. Why? Reading an x-ray report is something of a black art. Dark lines of varying fields of grey. To me they are indecipherable.  To a court judge, a tribunal member and an apposing engineer, they are just dark lines open to interpretation and misinterpretation. Even with the benefit of an in-person  assessment by an x-ray expert, the lines are meaningless and can easily be misinterpreted. These results can go either way in a court room unless they benchmarked.

The only way to establish a benchmark is to jackhammer and expose reinforcement at the same depths as you are ex-raying. That means that if you are relying on the results of an x-ray survey for the internal slab thickenings , you must first excavate and jackhammer and expose that same reinforcement elsewhere in the project to get a benchmark assessment of the accuracy of the results.

How X-Ray Reports Can Help

Once a reliable benchmark has been established and the x-ray results are deemed reliable, being able to establish the level of compliance in a slab is an amazing tool. Once concrete goes into a slab, the evidence is normally buried and it is nearly impossible to detect poor construction techniques. Such unidentified issues might be:

  • slab reinforcement too high or too low in the slab
  • wrong mesh size.
  • incorrect placement of footing reinforcement.
  • incorrectly placed strip footings
  • incorrect continuity of internal strip footings

The massive benefit that x-ray scanning has is the potential to check the construction of an entire concrete slab in one unobtrusive investigation. Probably a dodgy concreter’s nightmare come true.

 

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How to Identify and Fix Slab Heave