Alan B. Pearce wrote:

>>Other thoughts:
>>Concrete containing expanded polystyrene (styrofoam) 
>>is already fairly common.
>>Maybe you could just add some baking soda to your concrete? ;-)
>>    
>>
>
>Well, I was thinking of ping pong balls ...
>  
>

Eight years ago, or so, I worked for a company that made concrete 
batching control systems.  Liquids called admixtures are often metered 
to the batch to give the concrete various properties.  One common admix 
was called 'air'.  My boss once said (joked?) that some lesser quality 
plants just used dishsoap. 

Aaron
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