Air Content in residential concrete 2

[fp23]

What do you all call out for air content in residential concrete? Specifically foundation walls and footings. I've been revamping my general notes and have seen other engineers specify no air, 5-6%, or not mention it at all. No air seems to be the most common.

Based on the ACI I'm coming to the conclusion that footings and foundation walls should both be F1 at a minimum (maybe F2 for some foundation walls) and should have 5% air, although this feels a little conservative for the footings since they are at frost depth and the top of them probably won't see much freezing/thawing and/or water. Just curious if any of you have had pushback on this in the residential world.

 

[TRAK.Structural]

My notes say 6% (+/- 1%), but I would bet a lot of money that no one reads that

 

[Enable]

For Canadians, this is all spelled out via our performance classes (cut sheet). Might be useful as a guide for you. Also, one thing that's often overlooked is the construction cycle. While some items may not require an air entraining agent due to limited freeze-thaw exposure, during service, quite often footings / slabs / walls and the like go through a construction cycle that has them exposed to the winter elements. In which case, an air entraining agent may be a good idea.

 

[XR250]

Honestly, I rarely call out concrete strength or mix in residential.
I let the IRC handle it unless i actually need more strength.
Other than for strength, if I call out a mix, I am opening myself up to liability as I would appear as an "expert" in concrete mix design - which I am not.

 

[dik]

My notes say 6% (+/- 1%), but I would bet a lot of money that no one reads that

Yup 5% to 7%

 

[fp23]

Thanks all, helpful to get some other opinions. I think I'm going to leave it on there and see if I get pushback from anyone. Like TRAK said, i'm guessing that residential concrete subs are just going to keep using whatever mix they always do.

 

[phamENG]

I generated this from the durability requirements in ACI 318 and 332. Be sure to check it for accuracy before you use it. I delete lines that don't apply to the project, and edit if needed for additional strength or other performance requirements.

 

[JoelTXCive]

Are you located in a cold environment with a frost line? The air entrainment is more important if you are worrying about freezing temps.

 

[GaStruct]

I have the standard notes on my drawing per what ACI says. Like mentioned above, no one reads them.

Except for recently I had a homeowner GC that actually read them and asked for me to review the mix design. The local residential concrete supplier literally didn't have a mix to provide.

 

[phamENG]

The local residential concrete supplier literally didn't have a mix to provide.

Well, ya see, we add see-ment and rocks and some water, and it gets hard. What else you want?

 

[GaStruct]

It's just a "footer" after all.

 

[XR250]

4,000 for footings, Pham? That seems like a bit much. I suppose it will be 2,500 after they add the on-site water

 

[phamENG]

4,000 for footings, Pham? That seems like a bit much. I suppose it will be 2,500 after they add the on-site water

I'm in the swamp. All footings are in contact with water around here. W1 requires a minimum f'c of 4,000psi.

 

[dik]

i'm guessing that residential concrete subs are just going to keep using whatever mix they always do.

That's a bad idea in these environs... You need the entrained air for freeze-thaw cycles.

 

[fp23]

I generated this from the durability requirements in ACI 318 and 332. Be sure to check it for accuracy before you use it. I delete lines that don't apply to the project, and edit if needed for additional strength or other performance requirements.

View attachment 5275

Thanks pham. Why do you use 6% air for F1?

 

[phamENG]

Because it's the 'standard' (note other responses, above), and I'd rather have more than less, even with larger aggregate sizes. If the plant doesn't have a mix design that will work and they want to justify lower air entrainment because they larger aggregate, they can submit an RFI.

 

[jerseyshore]

We rarely add anything besides concrete strength to our notes. 3000 psi for most projects. 4000 psi for exposed or contact with water.

Seems like we always had issues with a specific air or W/C note. Commercial projects we'll usually get mix designs but for residential they're just grabbing whatever bag is closest to the door at Home Cheapo.

I do like pham's table though.

 

[gte447f]

Honestly, I rarely call out concrete strength or mix in residential.
I let the IRC handle it unless i actually need more strength.
Other than for strength, if I call out a mix, I am opening myself up to liability as I would appear as an "expert" in concrete mix design - which I am not.

@XR250 you don't even specify the concrete strength? Am I understanding that correctly? You must have used or assumed some value for f'c in your analysis or design, so why would you not put that on the drawings?

I recently reviewed a residential basement wall design that did not specify concrete strength, and that was the first thing that I noted in my review.

 

[XR250]

@XR250 you don't even specify the concrete strength? Am I understanding that correctly? You must have used or assumed some value for f'c in your analysis or design, so why would you not put that on the drawings?

I believe code requires 2,500 minimum. If I need it on the design, I will specify it. No one around here doing poured walls uses less than 3,500 anyway. I also don't think anyone sells less than 3,000 around here unless someone specifically asks.