Air or no-air for monolithic slab?

[TimberMan]

I ordered concrete today for my 26x30 monolithic slab with stem wall pour on Friday and I was asked if I wanted air or no-air in the mix. I wasn’t sure so I asked a few folks and got every answer possible.

I am using 4000 psi concrete for this enclosed barn but am not sure how to assess the strength of air vs the benefit.

All advice is welcomed.

Thanks

 

[JWILLIE1977]

Typically you want air entrainment for concrete that will be exposed to freeze/thaw cycles. Air entrainment allows for the expansion and contraction of the concrete under the freezing and thawing conditions.

Not sure if your application will be exposed to freeze thaw, or what the general use is. What is your desired finish?

Talk to your concrete finishers, as air in the mix can negatively affect hard troweled/burnished finishes.

 

[wssix99]

Overkill for a covered building. The benefits come outside where the concrete soaks up water and then freezes:

https://www.fhwa.dot.gov/pavement/concrete/trailer/resources/hif20085.pdf

 

[TimberMan]

Overkill for a covered building. The benefits come outside where the concrete soaks up water and then freezes:

https://www.fhwa.dot.gov/pavement/concrete/trailer/resources/hif20085.pdf

What about for the parts of the concrete that are outside like the exterior stem wall?

 

[Firebrick43]

What about for the parts of the concrete that are outside like the exterior stem wall?

No. Only flat work like sidewalks, driveways/aprins, and basketball courts need air entrainment

 

[ConCretin]

What about for the parts of the concrete that are outside like the exterior stem wall?

What wssix99 and others said is correct. You only need air entrainment in concrete exposed to freeze/thaw conditions and to water. You raise a good point about the exposed slab outside the garage doors. We have seen deterioration in these locations but it's unclear if it's caused by the non-air concrete or salts. The best option we've come up with is to use a good quality sealer to keep the moisture and calcium out. If you have a stem wall that is not integral to the slab you could use air in the concrete but vertical surfaces aren't as big a concern.

Why not use air entrainment for the whole slab? You could but you need to be aware of some potential pitfalls. When air entrained concrete is finished with steel blades, you run the risk of sealing the slab surface before air and bleed water have a chance to escape. The air and water actually pool under the surface creating voids that cause the surface layer to be unconnected from the underlying concrete. This is called de-lamination and is characterized by a surface layer that comes up in sheets with the slightest impact. This is especially likely in hot and windy conditions where the surface sets more quickly but you want to make sure your finisher knows what he is doing if you go this route.

 

[WNYflyer]

Should be spelled out in at least your State Residential Building code section R402 I believe.

 

[TimberMan]

What wssix99 and others said is correct. You only need air entrainment in concrete exposed to freeze/thaw conditions and to water. You raise a good point about the exposed slab outside the garage doors. We have seen deterioration in these locations but it's unclear if it's caused by the non-air concrete or salts. The best option we've come up with is to use a good quality sealer to keep the moisture and calcium out. If you have a stem wall that is not integral to the slab you could use air in the concrete but vertical surfaces aren't as big a concern.

Why not use air entrainment for the whole slab? You could but you need to be aware of some potential pitfalls. When air entrained concrete is finished with steel blades, you run the risk of sealing the slab surface before air and bleed water have a chance to escape. The air and water actually pool under the surface creating voids that cause the surface layer to be unconnected from the underlying concrete. This is called de-lamination and is characterized by a surface layer that comes up in sheets with the slightest impact. This is especially likely in hot and windy conditions where the surface sets more quickly but you want to make sure your finisher knows what he is doing if you go this route.

Super informative! Thank you!