Concrete Mix and AE?

[SteelPE]

I will admit that I really don’t know that much about concrete mixes so please forgive my question.

I have a project that is in the design phase in the north east. We will soon be issuing drawings in a dramatic race to beat the cold weather. The project is going to be constructed of tilt up panels. Due to the small site the panels are going to be cast on the SOG for the final building meaning that after the foundation is poured the SOG is coming next.

My concern is in the concrete mix for the slab. Usually we specify an air entrained concrete for concrete exposed to freezing and thawing temperatures during construction or during the life of the concrete. However, we avoid using an AE mix for slabs due to creating serviceability issues. Should I be concerned about not using an AE concrete mix for the SOG when it is will most likely be exposed to the freeze thaw cycles during construction?

 

[JAE]

The difficulty with air entrainment with slabs is that during hard troweling work the top 1/4" or so of the surface begins to get densified and this traps bleedwater rising and creates air pockets just below the surface (blistering). For tilt up wall panels, you may not be hard troweling to the extent that would cause concern.

With air entrainment the bleedwater comes up slower than without air so this sometimes fools the finishers who get on the slab for troweling too soon.

 

[dicksewerrat]

Are you designing the SOG for the bldg. service or the construction activity?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[Ron]

In my area, we use AE mixes routinely....and we have no freeze-thaw issues. Finish issues with AE mixes can often be alleviated with appropriate training of the finishers. In "hard" aggregate areas (low coarse aggregate absorption values), bleed water can be an issue as JAE noted. This can be corrected by proper mix designs using water reducing/air entraining admixtures.

If you have the potential for freeze thaw, use the AE mix.