Wall Honeycomb | Investigation and Repair 2

[bookowski]

I know this comes up here a lot and it ends up largely being a judgement call but - see attached photo. This is a basement wall, inside face. The rest of the wall so far is fine. This is the lower 1/2 of what will be a two story wall (i.e. this is subbasement to basement, upper 1/2 still to come). There are pretty distinct lines at each placement lift, looks like no one got in there with a vibrator.

The back face is stayform so I can't and won't be able to see it. I am thinking that I will ask them to core the wall in a few of the bad areas to see the inside of the wall.

- The top and bottom of wall are decent so it seems that rebar bond should be ok and shear ok. If the inside looks good then it's just a chip/clean and repair mortar fix?
- If the inside doesn't look good.... repair options (other than demo)?

 

[sandman21]

That's not just someone not using a vibrator, looks like they waited between placements and the concrete had time to set preventing mixing of concrete. If it were me they would be removing at least the three end panels, the next two panels they would hammered on until they found good concrete. Make sure they understand that you want to get an idea of the extent of the deficient concrete, and they should not overdo the removal. I would evaluate how deep the horizontal seam runs into the depth of the wall, if it appears to be full depth they would be removing those panels as well. The remaining two panels and column can be repaired using a standard detail.

 

[TehMightyEngineer]

Definitely get a number of cores of the bad areas and see what you're compressive strength is; you'll likely find it to be about 30 to 50% less than the good areas due to internal voids and poor bonding of the course aggregate. Also, you're going to have durability issues if this is a basement wall.

If it's just this one wall area I would highly suspect it's cheaper to demolish and replace than to repair. I went though a similar job with a basement foundation that was almost as bad (except it was the entire wall) but the site was remote so demoing and replacement of the concrete was extremely expensive, so we went with a repair.

My steps involved: calculations to prove the wall works structurally, coring and testing, chipping and grinding the repair areas, cleaning, bonding primer, SikaTop 123 PLUS repair mortar, heated enclosure (cold weather curing), carlisle wrap below grade (for durability concerns), backfill, waterproofing coating above grade (my project was a sand/salt storage shed so above grade durability and chloride resistance was paramount), reports and documentation throughout.

Easily cheaper and easier to demo and replace.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Archie264]

Well, whatever you decide, in da meantime don tosh dat wall…

 

[RHTPE]

You mentioned that the back face is StayForm - which means this was a one-sided forming condition. I can understand why you got this result - using a stiff mix and fear of vibrating the concrete and loosing much of the paste through the StayForm. Or worse, loosing the formwork. I suspect the crew was overly cautious.

Water-tightness may be a major concern, and is always a challenge with one-sided conditions. The final course of action will depend on what is required of the foundation wall. If it is required to be reasonably water-tight, then I would opt for full replacement. If not, then structural integrity will govern, and the previous recommendations are appropriate.


Ralph
Structures Consulting
Northeast USA

 

[bookowski]

Yeah the spelling might give a clue as to why they have problems building a wall...

Demo will not be an easy sell, they have several hundred linear feet of wall to go + the 2nd level of basement wall and then 20+ story superstructure - and of course they are pushing schedule. If it needs to come out it needs to come out but I'm hoping that's not necessary.

In the interest of showing this works does any of the following sound incorrect:
- I agree that there is a horizontal joint, I'll get coring here to verify that it goes all the way through. However, I am guessing that I can show that this joint works for strength pretty easily - mostly a shear issue and they are near midspan at a basement wall so likely a big cushion there. Any other issue with the joint?
- Durability: Outside face - I'm way above a water table, walls have insulation, w.p., drainage board and there is effectively zero soil here - these are lot line sites so 2" away is someone else's basement wall. Inside face we can repair/protect.

TME - to check strength did you use cores/breaks and redo your calcs based on these numbers? The 123 specifies max. of 1.5" lifts, is this how you did it? Seems like that will take forever. I was looking at the 111 which can be formed/poured in larger lifts.

They are going to keep going, no stopping them - so I'm thinking that worst case scenario we build a 'liner' wall later on in front of this one.

 

[TehMightyEngineer]

TME - to check strength did you use cores/breaks and redo your calcs based on these numbers? The 123 specifies max. of 1.5" lifts, is this how you did it? Seems like that will take forever. I was looking at the 111 which can be formed/poured in larger lifts.

We took cores and verified that the reduced compressive strength didn't change the calculations. We had a large thrust load on our wall from an arched roof so you'll likely have less strength requirements than we did (though you have a bigger building it sounds like). We assumed that the visibly acceptable areas of the wall had strength equal to the cylinders cast at time of the pour (which tested at the nominal design strength). We also found that the cold joints in our wall were entirely unbonded all the way through, and yours looks worse than ours. You'll want to verify that you can transfer the shear you need across this joint using shear friction assuming a cold joint.

SikaTop 123 PLUS is a good product. We ground the edges of the repair areas down 1/4 inch to give us the minimum thickness allowed (1/8" for SikaTop 123). In our deeper areas we filled them fully as they were typically only 1.5" deep. We did not demolish any concrete so essentially we used the SikaTop as a repair topping over the honeycombed concrete.

If you want to demolish large areas and repour then definitely something else is the way to go.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[DamsInc]

On that inside face, you've got lots of exposed steel that isn't surrounded by concrete, but that could conceivably be fixed. If you have the same condition on the outside face, then you've got durability (and structural) issues, even if you are above the water table. How would you verify that the outside steel is properly coated? If it's not, then how would you fix it?

 

[TehMightyEngineer]

DamsInc has a great point. On my wall we had access to both sides (and had issues on both sides). Thus I felt a lot more comfortable with a repair option, if I couldn't see the other side I would also be concerned.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[sandman21]

Any repair you do should be against sound concrete. They would need to remove until they reach sound concrete and then place the skia or other product onto that concrete. If the issue is thru the section they would be able to tell if they end to concrete and encase the entire rebar in repair product. If you can concerned about corrosion on the bar you can use a Penetron system to help protect the reinforcing. I would make sure the owner of the building understands the product they will be getting with the options you are considering.

 

[hokie66]

There is no evidence that any compactive effort was done. If this were a house, you might find a way to accept it. As the first step in building a 20+ level building, it cannot be accepted. I suggest looking for a better concreting subcontractor.

 

[TehMightyEngineer]

On hokie's note there is far more time and effort in repairing this than demolishing and replacement, don't let the contractor push you into something that's substandard. In the end you're saving them money by demolishing it.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[bookowski]

Thanks for the input/opinions - I have specified the wall to be removed and replaced.

 

[Ron]

Miserably underconsolidated concrete with at least two cold joints. Not salvageable in my opinion.

 

[bookowski]

Removing the wall - next question:

How to detail the new wall section to the existing footing. Should they sawcut close to base, then hand demo the remaining leaving that remaining several inches of wall dowels intact which can then receive couplers to the new wall vert bars?

 

[RHTPE]

Hopefully the footing is in much better condition.

Given the condition of the wall, it should not be too difficult to chip/hammer out, preserving all of the wall dowels coming out of the footing.


Ralph
Structures Consulting
Northeast USA