Chunk of concrete falling from the ceiling.
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So the principal had somebody from a construction company come today to look at it. He said it was indeed spalling, caused by a combination of rusting rebar and the rebar having been put too close to the bottom of the form in that spot during construction. He does not believe there is any risk to the structural integrity. We're now waiting on a second opinion from an engineer.
I'm quite glad this is going so smoothly.
I'm quite glad this is going so smoothly.
LightTamer
Member
I feel your pain with just being a student helping out at a school. I'm glad things got taken care of though... If the ceiling was falling at my school, i would have made sure every principle and teacher knew about it, and it looks like you've done the same.
Schools have a very tiny budget... they don't like spending much money on anything. It took me an entire day of talking to principles just to get the AC turned on in the room that our amps and dimmer rack is in. It's an AC about like what you would find in a house, and i was only requesting it run through the heat of the day (about 5 hours from 11AM to 4PM) to take care of the thermal errors we've had out of a few dimmer modules. Getting engineers and repairmen out to take care of things like what you're dealing with costs a good bit, and I'm not surprised the school fought it. I'm glad the principle listened though... The head of maintenance may need a little bit of help though... falling concrete, on a stage, with students under it, okay? Uh... no...
Schools have a very tiny budget... they don't like spending much money on anything. It took me an entire day of talking to principles just to get the AC turned on in the room that our amps and dimmer rack is in. It's an AC about like what you would find in a house, and i was only requesting it run through the heat of the day (about 5 hours from 11AM to 4PM) to take care of the thermal errors we've had out of a few dimmer modules. Getting engineers and repairmen out to take care of things like what you're dealing with costs a good bit, and I'm not surprised the school fought it. I'm glad the principle listened though... The head of maintenance may need a little bit of help though... falling concrete, on a stage, with students under it, okay? Uh... no...
From your comment and what I can tell of the photo, it sounds like the rebar is pretty much entirely rusted? Is that correct? If so that would be a big concern to me as the rebar is pretty important structurally and if that spot is rusted to that extent (without having been exposed long term), other sections could be as well.
I would also think that knocking down/removing the other loose piece would be a good idea at some point as it's not really going to be doing anything structurally and may eventually fall. It would also give another section of rebar to examine.
*I'm not a licensed structural engineer and this does need to be looked at by one. Also not saying for you to do anything yourself (though I wouldn't necessarily discourage watching/talking with the experts the school brings in).
I regret finding this post so late, this one is right up my alley.
So as it has already been mentioned, that is indeed spalling, in this case it was definitely caused by the rusting rebar. The rebar expands as it corrodes which places the concrete in tension (which we all know concrete is very weak in tension) and a piece gets blown out => TAADAA! Spalling occurs. I completely agree with the contractors assessment and would say that there is a much greater hazard from the falling debris than from the exposed rebar/spalled concrete. You can actually go around the ceiling and tap on the surface, you should be able to hear the difference where the concrete is sound, vs. delaminated. This may identify areas that the contractor needs to repair which aren't immediately visible at this time. Good move though to get a structural engineer involved.
To clear up a few things though, the concrete cover on rebar is very important to the overall strength of the system, Reinforced concrete structures rely on the bond between the rebar and concrete to develop tension in the rebar, which counters the compression in the concrete. This balance creates the flexural (bending) strength of the floor slab (or any other RC element). Without adequate cover this bond is greatly weakened and if seen over enough of the slab, serious problems could occur. Secondly concrete tends to get stronger as it ages, i understand that there can be a number of arguments against it, but structural concrete indoors, shouldn't get weaker.
If itll make you feel better i have seen much worse spalling and exposed rebar subject to moving truck loads under state highways, and they're holding up fine. A photo for comparison , this is a 5'x12' box culvert in New Jersey. (notice the ceiling of the culvert) The cause in this case was inadequate cover in an extremely moist environment.
The real question i haven't seen asked yet is, where is the moisture coming from that's rusting those bars?
Sources: BS Civil Engineering, BS Architectural Engineering, (Drexel University), 2 Years Underwater/ Substructure Structural Inspection
So as it has already been mentioned, that is indeed spalling, in this case it was definitely caused by the rusting rebar. The rebar expands as it corrodes which places the concrete in tension (which we all know concrete is very weak in tension) and a piece gets blown out => TAADAA! Spalling occurs. I completely agree with the contractors assessment and would say that there is a much greater hazard from the falling debris than from the exposed rebar/spalled concrete. You can actually go around the ceiling and tap on the surface, you should be able to hear the difference where the concrete is sound, vs. delaminated. This may identify areas that the contractor needs to repair which aren't immediately visible at this time. Good move though to get a structural engineer involved.
To clear up a few things though, the concrete cover on rebar is very important to the overall strength of the system, Reinforced concrete structures rely on the bond between the rebar and concrete to develop tension in the rebar, which counters the compression in the concrete. This balance creates the flexural (bending) strength of the floor slab (or any other RC element). Without adequate cover this bond is greatly weakened and if seen over enough of the slab, serious problems could occur. Secondly concrete tends to get stronger as it ages, i understand that there can be a number of arguments against it, but structural concrete indoors, shouldn't get weaker.
If itll make you feel better i have seen much worse spalling and exposed rebar subject to moving truck loads under state highways, and they're holding up fine. A photo for comparison , this is a 5'x12' box culvert in New Jersey. (notice the ceiling of the culvert) The cause in this case was inadequate cover in an extremely moist environment.
The real question i haven't seen asked yet is, where is the moisture coming from that's rusting those bars?
Sources: BS Civil Engineering, BS Architectural Engineering, (Drexel University), 2 Years Underwater/ Substructure Structural Inspection
I suspect the roof. I've not been up there proper myself, but I've looked out at it when inspecting the smoke hatches (that's another one of my threads), and it looks like the drainpipe hole is actually a couple inches raised from the level of the roof. Which would cause water to accumulate up there on top of the 50-year-old tar.
I wanted to, but didn't have time that day, to peek out one of those hatches and see if there was any standing water up there. I'll do that after the next good rain.
The thing about the moisture is that a leak may have already fully/partially saturated any insulation on the roof. Even if you see no ponding, it will still be getting through the tar and felt and sitting on the slab like a wet sponge. And it will remain wet even when there is no indication of moisture on the roofs surface. The only non-destructive way I've ever seen to find this condition is an infra-red survey. The moist areas show up cold on the images. The more destructive way is to cut a hole in the roof and get in there and see what's going on.
I don't think there's any insulation to speak of. I think it's (from bottom up) just the concrete, then tar, then crushed stone.
