air entrainment in garage slabs

[newtron]

Hi all, new to forum. I am pouring a garage floor slab and need your thoughts on air. The IRC requires air entrainment in residential garage slabs. I specified 5 or 6% air, 4000 psi mix. The place and finish sub advised me not to go with a steel trowel finish with air because of risk of delamination and scaling. I've poured several slabs and never had a problem. Have I just been lucky. Is delamination of slabs with air and hard trowel finish a common problem? Just how serious is the risk? Would you recommend going to a broom finish or ditching the air. I'm in Maryland, freeze thaw is a concern. Your thoughts are appreciated.

 

[MiketheEngineer]

Who pays if it fails??

 

[newtron]

I guess that would be me.

 

[MiketheEngineer]

While most garage floors I have seen are trowel finished - either accept the contractors recommendations and throw the onus on him or look to another contractor.

 

[Ron]

Not likely that the contractor will hard trowel the finish sufficiently to cause blistering, which is the issue with air entrained mixes with high water-cement ratio.

Keep the w/c down, use a water-reducing admixture, air content at around 5%, keep the slump to 4" +/- 1" and have at it.

 

[Hemifun]

Listen to your contractor. There is a chance of blistering and/or delaminations when you hard trowel air entrained concrete. See ACI 302.1R 5.7.1. I would recommend keeping the air and either eliminating the trowel finish or minimize your water content(slump) and delay the troweling until all the bleed water is gone and don't over trowel.

 

[newtron]

Thanks guys. What are most doing for a finish on garage slabs, troweling (w/o air) or just floating. A hard trowel finish would be nice for epoxy/ paint down the road.

 

[Ron]

newtron...actually a light broom finish is better for epoxy/paint later.

 

[newtron]

Thanks Ron, I didn't know that. I looked at neighboring garage slabs last night. They appear to be troweled but the owners don't know if air entrainment was specified or not. I'm going with the air.