> 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

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