Inadequate Cover Under Mat Foundation
Inadequate Cover Under Mat Foundation
(OP)
Just got an inspection report in for a 4'-6" mat that was poured 2 weeeks ago. The inspector notes that only 1" of cover was provided instead of the specified 3". Clearly this is not very useful 2 weeks out. I have notified the owner. Two questions:
- Owner is asking how it can be fixed. I hate to say that it can't, but short of pulling up 400 yards of concrete plus a story of walls I don't see any options?
- Beyond notifying the owner is there any other action to take?
- Owner is asking how it can be fixed. I hate to say that it can't, but short of pulling up 400 yards of concrete plus a story of walls I don't see any options?
- Beyond notifying the owner is there any other action to take?






RE: Inadequate Cover Under Mat Foundation
BA
RE: Inadequate Cover Under Mat Foundation
If the inspector observed that it was not correct, why wasn't it fixed before the pour?
Any chance it was shrinkage steel that he measured to?
RE: Inadequate Cover Under Mat Foundation
Definitely not temp steel, multiple rows of #9s.
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
This is way outside my area of expertise. However, I would think that something along the lines of the following could be done (hopefully by someone more familiar with the topic of corrosion than myself):
1) Establish some estimates about the degree of cracking and the rate of corrosion that will occur in reinforcement.
3) Explain to the client the expected reduction in design life of the structure / slab. Let the client (and lawyers) determine where to take it from there.
RE: Inadequate Cover Under Mat Foundation
Cathodic protection on contractors dime - that is interesting. That would really make them feel the pain.
Same job/contractor as the honeycomb wall I posted a while back (that was all torn out by the way) http://www.eng-tips.com/viewthread.cfm?qid=401760
RE: Inadequate Cover Under Mat Foundation
I believe you can monitor a cathodic system, so this might actually be an acceptable long term solution.
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
I hate to say it but I think that the concrete has to come out. I don't think that anyone other than the structural engineer should be blessing this as acceptable. And for you to assume the liability of doing that seems ridiculous. I have a hard time imagining an educated owner wanting to do this any other way either. Say you monitored it and discovered problems in ten years' time. What kind of rational remedy would there be?
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Inadequate Cover Under Mat Foundation
An expensive one. :)
RE: Inadequate Cover Under Mat Foundation
I really can't imagine removing it.
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
It's a shame that there's no way to sawcut some PT down into the mid-depth of the raft without interrupting the perpendicular topside rebar. If only one layer of several would be compromised, you could probably make up for that fairly easily.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Inadequate Cover Under Mat Foundation
Owners already alerted the contractor, as expected they say the inspector is wrong and they will meet with him (I'm sure to hang him over a balcony until he changes his mind) and produce pictures showing the cover. We'll see.
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
I don't know about low Ph but maybe that too could be determined.
Is 3" cover required for corrosion protection or is it required (for concrete placed directly against soil) as a way to be more certain that there is sufficient encasement to get bar development? (maybe both).
Seems like coring and evaluation the in place condition would be a good step before abandoning the sea in place.
What is the slab supporting? Big building or is this just for buoyancy resistance? (I've seen that before).
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
BA
RE: Inadequate Cover Under Mat Foundation
At the end of the day even if they submit signed and sealed repairs I'm on the hook. A tear out at this point is a huge deal so I'm not keen on rejecting a good idea to prove a point - but I'm having trouble imagining what their good idea could be. Is pressure grouting below the mat going to help/feasible/reasonable? Seems like the coring would need to be very frequent to ensure reasonable coverage. Combined with cathodic protection?
RE: Inadequate Cover Under Mat Foundation
1) Ask that a corrosion specialist be roped into the project at the contractor's expense.
2) Get the corrosion guy, contractor, and geotech at the same table.
3) Have the corrosion guy sign off on the fix with you nominally approving whatever they come up with?
This might ease your liability concerns and reduce the perception of your firm being the "bad guy". Basically, you delegate the bad guy job to someone more qualified.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Inadequate Cover Under Mat Foundation
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Inadequate Cover Under Mat Foundation
I don't plan on giving them this out though since this is a major screw up and don't want to take it on my shoulders.
The corrosion/repair specialist is the route I am suggesting.
RE: Inadequate Cover Under Mat Foundation
RE: Inadequate Cover Under Mat Foundation
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.