Gary Lindgren wrote:
> Scott,
> What strength are you looking for the mix you used. Was there any rock in
> the mix.
> Gary
> 

Gary,

No rock at all - I'm aiming for a matrix supported composite of (mostly) 
quartz sand and portland cement.  I'm hoping for over 6000 psi 
compressive strength at 28 days.  Ready-mix from a truck is usually 3000 
to 4000 psi.  If the difference in moist cured and air cured is 
substantial (should be), then further moist curing might produce 
significantly more strength.  Some mixes will gain another 60% in 
compressive strength if moist cured for a full year.

The compressive strength is not as much the goal as tensile strength and 
toughness, which both go up with compressive strength.  Unreinforced 
concrete beams like this usually fail in tension at the bottom, often 
from repeated light loads which cause hairline cracks to form and 
propagate.  Basically, I want to know how light I can make the base for 
my Lehman type device and still be confident it won't break with normal 
handling and thermal changes.

My wife makes root beer, I make fake rock.

Scott

-- 
A day without math is like a day without sunshine.

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