Concrete Double Tee Roof Spalling only bottom face.
Concrete Double Tee Roof Spalling only bottom face.
(OP)
I have been asked to look at some spalling that is occuring along the bottoms of some precast/prestressed concrete roof double tees in an industrail building. T
he span is very short (22') and the tees are 18" deep. The only load is dead load (self wt.) and a 40 psf snow load, so the loading is minimal for this span and type of construction. The building has been in place for roughly 40 years.
The spalling is occuring along the bottoms of the slab portions of the tees, and along the panel joints. None on the stems. Most of the spalls are about 2" X 2" and 1" deep or so. Some are larger, some are smaller. Most of the spalling appear to be recent, as chuncks of concrete are still on the floor in several places.
It is very stange. No loading changes, chemical exposure, or extreme temperature changes have occured as far as we can determine. The room that this is occuring is around 80 degrees F constantly, with a ceiling temperature around 100 degrees or so.
Has anyone seen anything like this? Any idea what could cause it at this point in time? Thanks! See attached pic.
he span is very short (22') and the tees are 18" deep. The only load is dead load (self wt.) and a 40 psf snow load, so the loading is minimal for this span and type of construction. The building has been in place for roughly 40 years.
The spalling is occuring along the bottoms of the slab portions of the tees, and along the panel joints. None on the stems. Most of the spalls are about 2" X 2" and 1" deep or so. Some are larger, some are smaller. Most of the spalling appear to be recent, as chuncks of concrete are still on the floor in several places.
It is very stange. No loading changes, chemical exposure, or extreme temperature changes have occured as far as we can determine. The room that this is occuring is around 80 degrees F constantly, with a ceiling temperature around 100 degrees or so.
Has anyone seen anything like this? Any idea what could cause it at this point in time? Thanks! See attached pic.






RE: Concrete Double Tee Roof Spalling only bottom face.
This looks like "pop-outs" caused by minor aggregate reactivity. It is unusual for the manifestation to take so long, but could also be a function of the minor nature of the reactivity taking a long time to build enough expansion stress to cause a localized failure.
RE: Concrete Double Tee Roof Spalling only bottom face.
RE: Concrete Double Tee Roof Spalling only bottom face.
RE: Concrete Double Tee Roof Spalling only bottom face.
RE: Concrete Double Tee Roof Spalling only bottom face.
Check the area in which the double-tees were cast and see if there is any history of minor aggregate reactivity. If I'm right, this is consistent with the presence of chalcedony chert, rather than an alkali-silica reaction that creates a large ettringite formation.
If ettringite formation, you'll likely see a crumbly, formerly gelatinous residue. If chalcedony chert, you'll see a powdery white to pale green residue in the middle of a small aggregate particle remaining at the apex of the popout.
RE: Concrete Double Tee Roof Spalling only bottom face.
RE: Concrete Double Tee Roof Spalling only bottom face.
Ron,
How is this different from ASR? And, I guess the big question, will these DTs continue to fail regardless of treatment?
As for why the flange only, I am guessing that has to do with the prestressing and exposure to humidity.
RE: Concrete Double Tee Roof Spalling only bottom face.
RE: Concrete Double Tee Roof Spalling only bottom face.
RE: Concrete Double Tee Roof Spalling only bottom face.
RE: Concrete Double Tee Roof Spalling only bottom face.
What is at the very bottom center of the picture transverse to the T-beams? It appears to have the pop-outs too but doesn't look precast.
What occurs in this facility?
RE: Concrete Double Tee Roof Spalling only bottom face.
RE: Concrete Double Tee Roof Spalling only bottom face.
RE: Concrete Double Tee Roof Spalling only bottom face.
As we've all surmised, it could be just about anything...past hangers for piping where the fasters were just pull out with the piping....fasteners shot from the top (though not commonly done), fastener corrosion...though you'd expect to see staining and some "pre-popping" cracks with stains....probably half a dozen other things.
Teguci...it is a form of ASR, it just doesn't form the classic ettringite gel...it initially expands volumetrically, causing the popout but prior to the gel formation.