Air entrained concrete Vs. Non Air entrained concrete

[dcredskins]

We specified 3500 psi non-air entrained concrete at slab on grade for a commercial project, and the GC poured 3500 psi air entrained concrete. Does it make a difference? I would appreciate your input.

 

[cvg]

air entrained is more durable where there is freeze thaw conditions

 

[Lion06]

For a situation where it is subject to heavy traffic I would say the non-air entrained would be bettter suited for durability. The air entrained concrete is better for freeze-thaw condition, not traffic. For heavy traffic, higher density is better (i.e. non air entrained).

 

[dcredskins]

cvg, do you mean we can use air entrained concrete under normal conditions as well when the concrete is not exposed to freezing and thawing or deicing chemicals?

 

[dcredskins]

StructuralEIT, however, as long as the compressive strength of the concrete is same, does it matter if you use air entrained concrete in lieu of non air entrained concrete?

 

[frv]

Agree with CVG.

If I remember correctly, a combination of air-entrainment and high w/c ratio would make delamination more likely; but if that hasn't occurred, you got some extra weathering protection for free.

Wouldn't worry about it.

 

[Lion06]

frv-
If this is an interior slab, why is weathering protection a consideration?
I would think that the traffic of the machinery would be much more of a consideration for the durability of this slab than weathering, no?

 

[cvg]

I don't believe we know if the slab is interior or exterior.

air entrained concrete is required by the state dot (Arizona) for highway pavement and other structures where freeze thaw is of concern. It is not required in other areas, but is still allowed. there are no other requirements for durability of the concrete pavement due to heavy traffic loading.

 

[Lion06]

I assumed commercial project meant inside, maybe not. There aren't too many commercial structures that are uncovered, are there?

dcredskins-
Is this slab interior or exterior?

 

[frv]

StructuralEIT-

Weathering isn't isn't a consideration. He just got it for free. I guess it's kind of like getting a free furnace here in Texas. Except you can't ebay air entrainment!

But now that you mentioned it, I think I do remember density being more important for high loading. Oh well. I still think it won't be a big deal unless he has a high percentage of air-entrainment.

 

[dcredskins]

StructuralEIT, it is inside.
frv, the compressive strength of used air entrained concrete is same as originally specified non air entrained concrete.

 

[frv]

dcredskins-

The fact that it's the same ultimate strength isn't really what StructuralEIT was alluding to.

Sure, if you were to put both cylinders into a compression test, they'd both do just fine.

The failure mechanism EIT is talking about, however, is due to cyclic loading. A heavy forklift won't come close to cracking the slab if it is only loaded a few times. However, each time the forklift is used, it damages the slab more than a non air-entrained slab. The micro-voids created by the air are more easily fractured than a more dense concrete.

 

[JAE]

The delamination concern is probably the biggest issue. Mostly if your slab was hard troweled.

With air entrainment, the bleed water in the concrete is inhibited more from coming to the surface and thus you run the risk of various degrees of air pockets formed just beneath the surface.

Depending on the mix, finish timing, etc., the pockets could be deeper or shallower and may not show up right away.

So the first order of business would be to look for delaminations. These would be found by visual inspection (looking for blister cracking), by chain drag (sounding for hollow sounds) or by coring (analysis of the cross sectional properties in the top layers of the slab).

There is also the behavior of air pockets formed from the vibration and dragging of the finishing blades during troweling, that develop air pockets even without bleed water effects.

 

[JAE]

Here's an article on the subject of air entrainment delaminations:

http://www.concreteinternational.co...e&keywords=delamination&srchtype=ALL&ID=13444

You must be a subscriber to see the whole thing.

 

[jike]

I would think that a "commercial" structure as described is an office, hospital, school, condo, etc. I would not think the floor is subject to fork truck loading or heavy machinery, etc. I would think that it would not make any difference as long as it achieves the specified strength.

 

[druminman]

I saw a presentation once where a million dollars worth of Terrazzo was delaminating from a slab in a hotel lobby because air entrained concrete was hard troweled. If memory is correct, the delamination didn't commence for a year or so.

 

[DonPhillips]

I remember reading something years ago from the Ohio Ready Mix Association that air-entrainment lowers f'c and you should allow for this in your mix design. Have you seen the cylinder break numbers? Are you getting results within the tolerances in ACI 318? If so, at least you did get the strength you were looking for.

I have not hear of delimination problems with floor finishes but I have heard of salamder-type heaters burning natural gas inside buildings during the winter, elevating the CO2 in the building and causing spalling when the surface was too brittle to withstand normal traffic.

Don Phillips

http://worthingtonengineering.com

 

[Atomic25]

Back when I was an intern as a site "engineer" for a six lane concrete roadway project in the north, the design mix utilized about 6% air, 3000psi, unreinforced, I think about 10" thick with dowel baskets every 15'. Sawcut above dowel baskets ASAP. Poured about 3 miles of that stuff and to this day hasnt cracked.

FWIW, proper sub grade prep is just as important as the concrete mix.

 

[frv]

DonPhillips-

I suspect this is something that would be taken into account by the concrete supplier. That is, a normal concrete may require a certain w/c ratio to achieve f'c, but an air entrained version may require a slightly lower w/c ratio to achieve the same f'c.

 

[JAE]

Atomic25 - for highways that doesn't surprise me. The problems come when you try to hard trowel interior floors with air. Highways don't receive that sort of finishing.