Lbear
Veteran Member
Posts:2740
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| 31 Jan 2024 03:07 PM |
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I noticed on an ICF wall (6" core), once the foam was removed for an electrical chase. There was a 45 degree crack running from a beam pocket corner. I talked with an ICF contractor and he said that this does happen, especially on corners like beam pockets or windows, where rebar is not immediately present. He claims the rebar in the wall will help control the crack and keep it structurally sound. He said most of the time, it will not be observed until foam is removed. Rebar schedule is 18" oc horizontal and 24" vertical
Should a crack like this be filled with high strength epoxy or just left alone? He claims to leave it alone for now and monitor it.
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ICFBdr
Basic Member
Posts:232
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| 01 Feb 2024 03:18 PM |
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Sounds like a shrinkage crack, which shouldn't be a structural concern. As concrete cures, it shrinks slightly. At the bottom of the beam pocket, the concrete is shrinking away from the corner vertically and horizontally creating the resulting crack at a 45 degree angle. You can see the same thing happen in sidewalks at the corner of a house.
You can always have a local structural engineer inspect to confirm and recommend any repair work to be safe. |
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smartwall
Veteran Member
Posts:1197
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| 01 Feb 2024 05:13 PM |
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I disagree. Concrete should not have noticable cracks, especially in an icf. The advantage of an icf is that it allows the concrete to slow dry, thereby less shrinkage. The rebar in concrete is to control micro fissures not cracking. All openings should have rebar diagonally placed in the corners as well as double rebar both vertical and horizontally around all openings. The reason concrete cracks is the addition of water to increase flow. Water is a filler that makes concrete weak. Tell a customer that the crack in their poured wall is normal or their sidewalk see what the reaction is. What else is the icf hiding? |
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Lbear
Veteran Member
Posts:2740
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| 01 Feb 2024 10:16 PM |
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The beam pocket was exposed to the air as the ICF stops there and the top of the finished concrete at the beam pocket is no longer contained within the foam. It is exposed to the air/wind/sun. The top of an ICF wall is usually exposed to the elements as that is where the pour stops and the concrete is vulnerable as it no longer has foam to protect it's curing. As mentioned, concrete likes to crack at 45 degree angles and especially from corners. Concrete is strong in compression but weak in
tension. Let's say a mix of a compression strength of 4,000 psi but it
will only have a tensile strength of just 400 psi. Rebars purpose is to increase the tensile strength of the concrete. With greater tensile strength, concrete is
better able to resist breaking under tension.
It is also true, to help flow, water is added at the job site to help with flow. So many factors at play like how long it took the concrete truck driver to get to the site. How hot is it outside. How long has the mix been sitting in the truck. Concrete trucks carry water on them as most of the time, water will need to be added at the site.
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smartwall
Veteran Member
Posts:1197
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| 01 Feb 2024 11:11 PM |
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Concrete should not crack. |
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Lbear
Veteran Member
Posts:2740
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| 05 Feb 2024 06:34 PM |
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Posted By smartwall on 01 Feb 2024 11:11 PM
Concrete should not crack.
Ideally, it should not but realistically it does crack, and hence why they saw cut expansion joints into slabs after pouring them and why rebar is added.
I don't claim to be an expert so that's why I ask others. I did ask the local concrete plant manager (40+years in the business) and he said concrete does crack. Not all cracks are equal but rebar and joints are meant to help stop the crack. He mentioned it usually comes out of corners on both walls and slabs.
A rounded object in the middle of a slab or wall creates the same problem as a
re-entrant corner. This is commonly evidenced around slab & wall penetrations
such as pipes, plumbing fixtures, drains. The
concrete cannot shrink smaller than the object it is poured around, and
this causes enough stress to crack the concrete. Because the concrete cannot shrink around a corner, the stress will
cause the concrete to crack from the point of that corner.
Per The American Concrete Institute addresses this issue in ACI 302.1-04.
“Even with the best floor designs and proper construction, it is
unrealistic to expect crack-free and curl-free floors. Consequently,
every owner should be advised by both the designer and contractor that
it is normal to expect some amount of cracking and curling on every
project, and that such occurrence does not necessarily reflect adversely
on either the adequacy of the floor’s design or the quality of its
construction (Ytterberg1987; Campbell et al. 1976)”. |
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smartwall
Veteran Member
Posts:1197
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| 05 Feb 2024 07:49 PM |
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I walk every day.. In upstate it snows and we have freezing rain, so I go to my local Walmart and walk the store for an hour. Probably 100,000 sq ft at least. Haven't found a crack in the floor yet. Maybe under a cooler. I'll have to move one. When the weather is better I walk along a road near my house. 2 miles of sidewalk done 4 years ago not a crack in site, even with commercial vehicles crossing them on a daily basis. It must be magic concrete. |
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Lbear
Veteran Member
Posts:2740
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| 05 Feb 2024 09:06 PM |
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Posted By smartwall on 05 Feb 2024 07:49 PM
I walk every day.. In upstate it snows and we have freezing rain, so I go to my local Walmart and walk the store for an hour. Probably 100,000 sq ft at least. Haven't found a crack in the floor yet. Maybe under a cooler. I'll have to move one. When the weather is better I walk along a road near my house. 2 miles of sidewalk done 4 years ago not a crack in site, even with commercial vehicles crossing them on a daily basis. It must be magic concrete.
You probably need better glasses 
Your argument is not with me but it's with the engineers and the American Concrete Institute. Maybe let the ACI know that they are wrong and need to revise their manuals and standards?
The Home Depot's, Lowe's, Walmart's, Costco's, etc all have cracks in their floors out here. Maybe it's just a regional thing? We might need to import our concrete from New York.
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ICFBdr
Basic Member
Posts:232
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| 06 Feb 2024 03:47 PM |
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Three certainties in life: death, taxes, and concrete will crack. The key is having the correct reinforcement (size, spacing, and location), pouring conditions, and mix to minimize these cracks. Control joints are cut into slabs in hopes that cracks will occur within these cut lines and not be visible, for example (good practice is to include a cut at a 45 degree angle from a corner to hide the expected shrinkage crack as noted above). A technical manual on concrete curing I read several years ago included +/-8 different types of cracks in concrete (my memory may be a bit off on the exact number). These included shrinkage cracks, delamination, stress cracks, etc. Some of these can be very concerning structurally, while others are simply cosmetic. It is true that concrete cured inside an ICF form is given a slower curing environment, thereby reducing the chances of cracking (concrete poured exposed to sun/heat/wind is much more likely to crack from curing too quickly following placement), but it is still possible for cracks to occur.
We are all making some broad assumptions about your wall. Best bet is to have a local inspector/engineer to take a look and confirm if it is OK or needs remediation of some sort. |
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Dilettante
Advanced Member
Posts:503
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| 25 Apr 2024 10:53 AM |
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I beg to differ. Mostly jokingly. There are two types of concrete. - Concrete that is cracked
- Concrete that has not yet cracked.
There are things that can be done to minimize cracking and cover the cosmetic appearance of micro-cracking.
This is not to say one should just "like it or lump it".
You just need to have your mix and pour schedule PLANNED by people with lots and lots of experience.
Calling "Cousin Bubba" over to "Mix y'all some CEE-MENT" IS UTTERLY CONTRAINDICATED.
Posted By smartwall on 01 Feb 2024 11:11 PM
Concrete should not crack.
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Dilettante
Advanced Member
Posts:503
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| 25 Apr 2024 11:02 AM |
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What he's seeing is polished concrete floors. These are floors that's are crack-filled, then sanded down, sealed and polished. And, even then, they NOT really perfect and crack-free. Also they're poured in smaller individual slabs and numerous, larger expansion joints between the slabs.
Posted By Lbear on 05 Feb 2024 09:06 PM
Posted By smartwall on 05 Feb 2024 07:49 PM
I walk every day.. In upstate it snows and we have freezing rain, so I go to my local Walmart and walk the store for an hour. Probably 100,000 sq ft at least. Haven't found a crack in the floor yet. Maybe under a cooler. I'll have to move one. When the weather is better I walk along a road near my house. 2 miles of sidewalk done 4 years ago not a crack in site, even with commercial vehicles crossing them on a daily basis. It must be magic concrete.
You probably need better glasses
Your argument is not with me but it's with the engineers and the American Concrete Institute. Maybe let the ACI know that they are wrong and need to revise their manuals and standards?
The Home Depot's, Lowe's, Walmart's, Costco's, etc all have cracks in their floors out here. Maybe it's just a regional thing? We might need to import our concrete from New York.
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