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.