deciphering air entrainment requirements

[boffintech]

The summerized specs read:
for normal weight concrete air content =
•no entrained air for concrete placed in foundation
•5% +- 1.5% entrained air UNO
•3% +- 1.0% entrained air for mixes with compressive strength greater than or equal to 5000 psi
•4% +- 1.0% entrained air for mixes with compressive strength less than or equal to 5000 psi placed in aggressive

(Aggressive environment = Exterior)

So for slab-on-grade with interior exposure and placed with 4000 psi concrete the air requirement is ______?

By the specs given it's either 5+-1% OR the member is considered part of the foundation and thus no A/E required.

 

[dik]

For SOG interior exposure, I'd spec 0-3% to accommodate entrapped air. No air entrainment necessary... Air entrainment does, however, help with placing concrete.

I'd read your specs as having to conform to #1, 3.5 to 6.5. I think the spec writer has 1 and 3 confused. Should have higher for exterior exposure if freeze-thaw is an issue.

Dik

 

[miecz]

Agree with dik. The spec asks for 5%+-1.5%. I would check with the engineer to verify this requirement, particularly if the slab has a mineral aggregate hardener or is trowel finished.

 

[boffintech]

I understand the conclusion; however, is it possible that the EOR considers S-O-G, retaining walls, and foundation walls as "foundation" and thus no A/E required?

On the general notes page of the structural drawings under the FOUNDATION section there are notes on footings, foundation walls, drilled piers, s-o-g, retaining walls, soil density, bearing capacity, etc.

He must be considering s-o-g as "foundation", right? That's the only way his A/E criteria make sense. Also makes more sense considering the vast majority of interior slabs get trowel finish. 6 1/2% + trowel = delamination right?

What say you guys?

 

[Ron]

Agree with dik...interior application, so air entrainment not necessary; however, there is ambiguity in the specification so it requires interpretation by the author or the engineer in responsible charge. Submit an RFI.

 

[miecz]

I don't think of the slab-on-grade as part of the foundation. However, I don't know of an official definition that would rule it out. If your EOR has slab notes under the Foundation section, then he/she may consider it as such.

From what I've read, steel troweling of slabs with 5%+-1 1/2% air can contribute to blisters, finishing problems and weak concrete at the surface.

 

[dik]

Generally... for an ambiguity in the contract, the courts rule against the person who drafted the contract...FWIW

Dik

 

[henri2]

boffintech, a few questions for you.

1. Is this project a building?

2. Is the project located in a a region where air-entrained concrete is typically specified for freeze-thaw resistance?

3. If the answer to the preceeding question is negative, do you know why air-entrained concrete was specified?

 

[boffintech]

henri,
1, yes
2, yes

The given criteria do not cover all possible concrete members on the job. If the first criteria were changed to read,

•no entrained air for concrete placed in foundation or in slabs, walls, and columns with interior exposure

the specs would work better.

But if one goes "by the book" interior slabs could have as much as 6.5% air.

 

[soflapoolboy]

What method of concrete placement will you be using?
1. Gunite (dry mix)
2. Shotcrete (wet mix)
3. Cast in Place

If your using Gunite, I don't think an air entraining admixture can even be added.

 

[boffintech]

3. cast-in-place

 

[DRC1]

The slab has the 5% +/- 1.5%.
If the footings (not the pedestals necessarily) are founded below frost, A/E would not be necessary. The slab could be subjected to freeze thaw and therefore needs A/E.
Even if it does not need A/E, it does not hurt. Never had trouble w/ finish w/ up to 7% A/E. I would define agressive as corossive. So if 4%+/- 1% is wanted, it should be clearly called out on the drawings. A/E is not that big a deal. Someone seems to be overthinking the problem. What does the engineer say?

 

[boffintech]

I guess I am guilty of over-thinking the problem. It seems that this is one of those specs that is not all inclusive. The EOR tells me that the interior elements do not require A/E because ACI318 does not require it: elements not subject to freeze/thaw. Using the criteria in the specs isolated from ACI318 was the problem.

 

[DRC1]

I was not refering to you as overthinking the problem. I was refering to the designer. Seems like a very detailed spec for A/E. Certianly given the specification you need to understand it and be sure it is properly implemented. I just think the designer could have made life a little simpler. I would hate to see the rest of the spec.
I feel the spec should be able to stand alone as much as possible.
So does he consider the slab on grade to require A/E?

 

[boffintech]

He does not consider the interior s-o-g to require A/E.

Going exclusively by the spec the interior s-o-g would require A/E. But since this element is not being subjected freeze/thaw, ACI318 does not require A/E. That's what I have been told.