Clay unintentionally included in concrete mix
Clay unintentionally included in concrete mix
(OP)
I have a unique situation that came up in the last week, that I'd appreciate some opinions on.
We have a wastewater tank that has bolted steel glass lined walls with a concrete floor. The slab was poured about a year ago, and there are several concrete spalls 1"-2" in diameter dispersed randomly across the tank floor with no obvious external cause. We had some cores taken of the concrete, including directly at a couple of the spalls, and the preliminary tests have found a small chunk of bentonite clay at the base of the spall. Concrete quality appears to be normal other than the clay.
We theorize that the concrete ready-mix plant was scaping the bottom of the aggregate pile and let some clay get into the mix.
The tank has an aeration grid installed across the slab, which complicates the placement of some sort of coating, but the aeration grid can be removed if needed. We are discussing recommending a poly-urea coating, but if water were able to find its way under the coating, say at the seal between the coating and the glass lined wall, and swell more of the bentonite, it could possibly delaminate the coating. I'm not too concerned with the structural capacity of the floor, since its primary function is water-tightness, although we do suspect that the perimeter ring-wall also has clay mixed in, but it would be well contained by reinforcement (except for the outer 2" clear cover). We suspect that the underside of the slab is also covered by random spalls as well.
Has anyone come across this problem before? What sort of things might I not be considering? Does anyone have any suggestions for repair of this problem or opinions on the effectiveness of a poly-urea coating?
Thanks in advance!
We have a wastewater tank that has bolted steel glass lined walls with a concrete floor. The slab was poured about a year ago, and there are several concrete spalls 1"-2" in diameter dispersed randomly across the tank floor with no obvious external cause. We had some cores taken of the concrete, including directly at a couple of the spalls, and the preliminary tests have found a small chunk of bentonite clay at the base of the spall. Concrete quality appears to be normal other than the clay.
We theorize that the concrete ready-mix plant was scaping the bottom of the aggregate pile and let some clay get into the mix.
The tank has an aeration grid installed across the slab, which complicates the placement of some sort of coating, but the aeration grid can be removed if needed. We are discussing recommending a poly-urea coating, but if water were able to find its way under the coating, say at the seal between the coating and the glass lined wall, and swell more of the bentonite, it could possibly delaminate the coating. I'm not too concerned with the structural capacity of the floor, since its primary function is water-tightness, although we do suspect that the perimeter ring-wall also has clay mixed in, but it would be well contained by reinforcement (except for the outer 2" clear cover). We suspect that the underside of the slab is also covered by random spalls as well.
Has anyone come across this problem before? What sort of things might I not be considering? Does anyone have any suggestions for repair of this problem or opinions on the effectiveness of a poly-urea coating?
Thanks in advance!






RE: Clay unintentionally included in concrete mix
BA
RE: Clay unintentionally included in concrete mix
BA
RE: Clay unintentionally included in concrete mix
But I'm not sure the coating will help. Is it supposed to seal the slab, to prevent the pop ups from, well, popping up. There's probably enough trapped moisture already in the concrete to activate the clay. And the polyurea won't help that. And if the project has any kind of groundwater, the moisture will come up from the soil.
I'd go with the laborious approach. Get those pop ups, dig out the clay chunks and repair them one-by-one with a Sika product, like Sikatop 123. This might be the owner's issue for a long time. The GC should be responsible for some of the costs, but if it's more than a couple of years, good luck with that.
RE: Clay unintentionally included in concrete mix
Dik
RE: Clay unintentionally included in concrete mix
Since these pop-outs are the result of rain water, I'm not convinced that there are not more pieces of clay that haven't yet swelled and created pop-outs. Once the tank is put into service, it will be exposed to water close to 100% of its lifetime, and leaks from the floor of the tank are not always obvious or even detected. This is why I was initially leaning towards a coating to restore the water-tightness of the floor. Hope this helps you understand my dilemma.
Thoughts?
RE: Clay unintentionally included in concrete mix
The original wall has spalls, but ought to be still strong enough to serve as a gravity retention wall.
RE: Clay unintentionally included in concrete mix
http://www.americanbar.org/publications/probate_pr...
RE: Clay unintentionally included in concrete mix
On residential jobs, I have seen builders pour slabs with the use of a pump truck. They will often have leftover concrete or maybe a little pump time leftover if the pump price was negotiated at a flat fee.
Anyway, they will pour flatwork (driveway sections & walkways) with the extra concrete and use the pump truck.
There are no vapor barriers under the flatwork sections, and often no leveling sand or base material other than natural earth. When concrete blasts out of the pump's elephant trunk and hits the ground; it can displace large blobs of clay (in Texas) into the wet concrete. Some of these mud blobs will end up near the surface and create large holes. I've seen 1"-2" golfball sized holes all the way up to 3-4" baseball size holes.
RE: Clay unintentionally included in concrete mix
RE: Clay unintentionally included in concrete mix
RE: Clay unintentionally included in concrete mix
RE: Clay unintentionally included in concrete mix