Cold Joint in Pad Footings
Cold Joint in Pad Footings
(OP)
I was on site today and found a condition I had never seen before....a pad poured half way.
By half way, I mean half way across, full from bottom to top, with the rebar sticking out of one half of the pad.
The contractor said he had ran out of concrete and was going to pick it up next week. There is just this rough, lumped
over blob of concrete, formed on 3 sides.
Before I dive into the ACI what do others have to say on the matter ?
Thanks.
By half way, I mean half way across, full from bottom to top, with the rebar sticking out of one half of the pad.
The contractor said he had ran out of concrete and was going to pick it up next week. There is just this rough, lumped
over blob of concrete, formed on 3 sides.
Before I dive into the ACI what do others have to say on the matter ?
Thanks.






RE: Cold Joint in Pad Footings
RE: Cold Joint in Pad Footings
You usually avoid cold, vertical joints in areas of high shear.
For a spread footing with a column/baseplate in the center, and a joint across the pad, it seems that the moment in one direction would be OK - perpendicular to the "span".
And it would seem that the moment in the other direction is unaffected.
Shear for a two-way slab is one way and also punching - both may not be too affected by the joint as it doesn't occur at the critical sections.
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RE: Cold Joint in Pad Footings
I would think the 'blob' would likely cause an unsightly finished joint and cause surface cracking and breaks. You may need them to sawcut a clean line down without cutting through rebar and demo a vertical-ish surface and then rely on aggregate interlock/friction
EDIT: I read that as in a slab. So pardon if not applicable,
RE: Cold Joint in Pad Footings
Less than ideal and the moment is max near the halfway point if the column is centered. BUT, concrete flexural design assumes that it's the section is cracked anyway, so what's the difference.
And generally speaking a rough surface is GOOD for a cold joint.
Are there anchor bolts affected?
RE: Cold Joint in Pad Footings
One thing I didn't think about was the anchor bolts - I would think that a cold joint near an embedded anchor might be problematic per Appendix D*
*Appendix D s%#ks
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RE: Cold Joint in Pad Footings
In my opinion, if they want to save the blob of concrete, the surface demo for a clean aggregate surface, water or sandblasting to clean the surfaces and application of bonding agent which I would require would far outweigh the costs of yanking the existing blob out with a loader and starting over. Not to mention the additional time you would have to deal with detailing/explaining all this to the contractor and likely all the back and forth that will likely accompany it.
RE: Cold Joint in Pad Footings
The contractor should have called for a cleanup and he didn't. Make him do it right.
Mike McCann, PE, SE (WA)
RE: Cold Joint in Pad Footings
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: Cold Joint in Pad Footings
KootK has beaten me to the issue of shear, as the moment and shear are both maximum in cantilevers.
In addition, the first pour of concrete as described cannot be well compacted, as there was nothing to restrain the side with the "rough, lumped over blob".
RE: Cold Joint in Pad Footings
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: Cold Joint in Pad Footings
That doesn't make it good workmanship or acceptable, though.
On the other hand, if the footing isn't overly thick and there's steel top and bottom and the interface isn't too close to one side, this could actually edge towards acceptable. Stupid, but maybe acceptable.
RE: Cold Joint in Pad Footings
Think about this - there are vertical and roughened or keyed construction joints placed in elevated beams and slabs all the time - usually placed intentionally near points of maximum moment but also kept away from high shear areas.
The vertical joint in the footing - directly at a centerline - would not be a high shear area as long as the concentrated load is spread out a little - either with a base plate or via a concrete column.
But all this above is under ideal conditions so a "blob" of concrete and messed up subgrade would certainly be a concern.
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RE: Cold Joint in Pad Footings
I agree, there would be some capacity. But how would one calc it out? You would basically be relying on the tensile stress capacity perpendicular to that very cold, rough, diagonal joint to resist diagonal tension. What does that take from a preparation and verification standpoint? Is there some kind of ASTM pull off test that would be appropriate?
While this would likely be true for one way shear, the two way shear demand in many pad footings leaves little reserve in the tank. And this cold joint pseudo shear crack may well be 1/4 of what might become the critical punching shear perimeter.
You may not have interpreted my sketch as intended JAE. In my sketch, the diagonal line is not a shear crack but, rather, the cold joint itself that has the potential to become a critical shear crack. Bigmig has yet to clarify this but I've assume that the as built interface is a sloping surface, not a vertical one. I've also assumed that the joint is near centre but not necessarily at centre. As I mentioned in my last post, if the interface is vertical, or is made vertical, I'm fine with it as a shear friction joint that will benefit from high moment if not, simultaneously, low shear.
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: Cold Joint in Pad Footings
Mike McCann, PE, SE (WA)
RE: Cold Joint in Pad Footings
If the joint is vertical and "half way" through the middle as the OP suggests, then I see no problem.
If it is a sloping "blob" then per your sketch shear might be an issue.
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RE: Cold Joint in Pad Footings
If we use "The Blob" analogy wouldn't the foundation shrink in cold weather?
RE: Cold Joint in Pad Footings
The problem is the concrete, which goes into compression at this mystery joint when that pad loads. If there are voids or anomalies of any type at the contact point between pours, they will collapse or slip to a point of equilibrium. I'm going to be directing them to pull this pad Monday.
RE: Cold Joint in Pad Footings
Mike McCann, PE, SE (WA)
RE: Cold Joint in Pad Footings
You may be able to justify shear capacity with the Canadian code (although maybe not, because if you don't some reinforcement through it the equation will kind of explode because of the way it's set up and whether you'd want to without bars holding back shrinkage is another question) but pretty sure you couldn't with ACI. You wouldn't be able to justify tensile capacity by code.
From a realistic standpoint, there's capacity along that joint. From an engineering standpoint, like I said before, I wouldn't allow it.