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Questioning the results of RH probes

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I have come across this situation on many if not all of my long term moisture testing jobs and it is starting to get to me. I find that when taking initial readings (after the 72 hours) my results are typically high (90s or at least high 80’s). When I return to the site for regular readings and plot all of the data I find that the test locations in general will gradually come down in RH until we stop testing or until they reach the desired levels and they are covered. Occasionally we get some that do not come down at all but the gradual lowering of the RH over time is more common.

While this sounds good and appears to be doing what the concrete does over time under the right conditions, the part that scares me about the validity of the RH testing is that this will be typical on my jobs where the slab was poured 8 months ago just the same as slabs that were poured 20 years ago.

Yes I know that the slab poured 20 years ago may have been covered immediately back then and never dried out, had some recent problems where the concrete was wet or some other strange occurrence to make the concrete have a higher RH again but it is a regular occurrence that they start off with high RH values and slowly lower over weeks or months of testing.

The main point is that I have not seen a slab that is initially at a reasonable RH and has already stabilized. It always seems to be starting it’s drying out process the moment I start to monitor it.

Any thoughts?
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Messages In This Thread
Questioning the results of RH probes - brian - 10-13-2011, 01:06 PM

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