> > I am curious as to what pumping air into the concrete does.  
> > I am getting ready to pour some concrete.  Should I know 
> > about this before I start the project?
> 
> 
> Makes it weaker.  Vibrating or compacting it gets the air out.  If you're
> just pouring a floor for a small shed I wouldn't worry about it too much.
> 
> When you see a pipe connected to a compressor or such stuck in the concrete,
> that a vibrator.  It agitates the mix so the bubbles travel upwards.
> 
> On the other hand, very small bubbles are sometimes added to the mix to make
> it handle frost better.  The name for this escapes me at the moment.
> 
> Tony

Air Entrainment. Pretty important for outdoor concrete in freezing climates.
http://en.wikipedia.org/wiki/Air_entrainment

-Denny


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