Horizontal Concrete Wall Crack

[stiffener]

We conducted an observation of an 8" by 5'-0" continuous foundation wall recently and observed something that we had not seen before. We observed that the wall has horizontal cracks approximately 3" from the top of the wall on both sides. The wall is approximately 40' long, but the cracks don't appear along the entire length. The wall appears to have been placed directly on ledge on a very steep site. This foundation wall makes the front wall of a unheated crawl space with low and balanced back fill on each side. Both the foundation wall and wood framed wall above checked as plumb. We observed no diagonal or vertical cracking. There is a large cantilevered deck above the wall and we originally thought the damage might be from uplift, but we observed no damage or separation to the wood wall framing, which is all exposed, and the building has no tension resistance system in place other than the exterior sheathing. There is no visual damage to the finished residential space above. So our working theory is that the reinforcing along the top of the wall is corroded due to chloride in the concrete mix design. There is no water staining/damage or visual corrosion that we would normally see. We are wondering if anyone else has seen damage similar to this.

 

[stiffener]

Here is another photo of the interior of the wall.

 

[oldestguy]

You may be correct,but why not chop out some to get a look. Otherwise would it be result of running out of concrete a few inches short of top and later adding a sloppy filler?

 

[OldBldgGuy]

The cracking is pretty severe. Knocking some of the concrete out of the way isn't making anything worse; then you can see what's in there. I can't come up with any idea other than your corroded rebar. The top of the wall has lifted and the spalled pieces on the sides have pushed out both interior and exterior, which certainly looks like something in the walls has gotten bigger. If it's not reinforcing, what is it? I've seen bentonite tape burst a wall when placed too close to the surface, but who's putting a waterstop tape in that location?

 

[BAretired]

My guess would be settlement of the concrete. The upper portion was held in place by reinforcement which can't settle because it is tied to the vertical bars.

BA

 

[stiffener]

The drawings that we do have only show horizontal reinforcing. With no diagonal or vertical cracks, settlement didn't seem to be the answer. Also placed on ledge.

 

[XR250]

Head scratcher for sure. I second corrosion jacking.

 

[msquared48]

Probably the corroded rebar scenario, but that would take time...

Two questions:

1. How old is the concrete wall and the wood framing above? New construction?

2. Also, has the wall seen a large uplift force from wind that could cause a crack to develop at an unconsolidated horizontal pour joint?

In looking at the shot along the wall to the left side of the photo, it seems like the wall bends back to the right... An illusion?

Unless the crack literally formed as the concrete was curing from local consolidation , I would think, based on the wall height and horizontal reinforcing, that the stiffness of the wall could span any soft spots in the soil matrix after it cured.

Puzzling problem here...

Mike McCann, PE, SE (WA)

 

[msquared48]

Another thought is that the contractor vibrated the outside forms rather than the wall internally. If he had forgotten to vibrate the wall and was told to do so after the top of the wall above the crack had set, the crack seen could be the result after the wall concrete below the crack had settled.




Mike McCann, PE, SE (WA)

 

[stiffener]

The building was constructed in the 80's. We originally thought it may have witnessed a large uplift event and there is a 6' cantilevered deck above the wood wall along the entire length of the wall to support the theory. But there is no separation in the wood framing at all to signify a big event, there is no uplift tie system in place to concentrate load, and no damage to the finished walls above. All the walls are placed on ledge so there shouldn't be any settlement and there are no vertical or diagonal cracking. You are correct about the picture being an illusion. It is plumb.

There is evidence of poor vibration with "rat holes" in a couple of areas.

The building is located right off from a ocean harbor so there would be plenty of chloride in the air. The drawing is also showing (2) rows of reinforcing at the top of the 8" wall. We found one area away from the cracking on the interior where the reinforcing has no cover. So our thought is still lack of reinforcing cover and chloride corrosion. We will recommend opening it up to confirm.

 

[Jerehmy]

What is the age of the crack. It's hard to tell from the photographs, but it doesn't look that old. Was there dust/debris buildup inside the crack?

 

[stiffener]

As typical, they couldn't tell me the age, but you are correct that it doesn't look that old given the lack of debris and dust.

 

[Jerehmy]

I agree that some destructive investigation is definitely warranted here. Will likely tell you all you need to know. Some of the chunks look like a few good whacks from a mason hammer and they'll pop right out.

 

[msquared48]

So, voids created from lack of consolidation or inadequate rebar spacing relating to aggregate size, leading to water intrusion, rusting of the reinforcing, expansion and deterioration.

Gee, where have I seen this before?

Mike McCann, PE, SE (WA)

 

[BAretired]

I don't want to beat a dead horse, but I still think it looks like settlement. If there were no vertical bars, perhaps the top horizontal bars were resting on form ties which prevented them from settling along with the lower portion of wall.

BA

 

[msquared48]

Bear with me here...

Hard to believe for me BA considering what I mentioned before, as the crack was not along the entire length of the wall...

I would expect some diagonal cracking to be seen from settlement / rotation, unless the wall settled uniformly, where I would see the crack along the entire length of the wall. If uniform settlement also occurred, you could see some diagonal cracking along the end transverse walls, unless the building rotated or settled as a whole.

This is a can of worms...

Mike McCann, PE, SE (WA)

 

[BAretired]

Hi Mike,

I hadn't noticed that the crack wasn't full length but it is possible that horizontal bars were placed below the form ties in some locations and above the ties in others. The type of settlement I was considering was the settlement of concrete in the form as it sets, not foundation settlement although that could be a factor as well.


BA

 

[msquared48]

OK. I understand.



Mike McCann, PE, SE (WA)

 

[chicopee]

Is the house subject to being battered by storms such as Sandy since it is by the ocean?

 

[chicopee]

I would also check the entire perimeter of the foundation.