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RE: Lightweight Concrete

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Call the supplier of the light weight aggregate in your area.  They will
have all the information that you need and more. Don't rely on the concrete
supplier for information.
If your light weight is predicated on a UL assembly.  Look at the specifics
of that UL assembly, and design your mix on the upper end of the range, even
if you have a slightly thicker slab.  The other thing is to ask if you can
use the density at equilibrium as opposed to 28 days.  The ASTM is in the
process of changing to equilibrium, but it is not there yet.
By using the upper end of the density, you will be able to pump better, and
the finish will be better.
In general 115 pcf is fairly easy to pump and finish (the lower the density
the more air entraining, the more difficult to finish).  The 115 pcf mix
will have a wet density of about 121 pcf.
Harold Sprague
The Neenan Company 

-----Original Message-----
From: Robert Rollo [mailto:rrollo(--nospam--at)]
Sent: Tuesday, July 27, 1999 2:26 PM
To: 'seaint(--nospam--at)'
Subject: Lightweight Concrete

anyone have experience with lightweight concrete deflecting more than
calculations indicate? 

conventionally reinforced. 
got the reduced E due to lightweight. 
got the reduced fr in the cracking moment calc. 
still get more measured deflection at 150 days than calculated delta dead
plus 1/2 of total creep. 

any common experiences with such in lightweight (spec'd as <115pcf, 4000psi)

actual 28 day breaks exceed 4500psi. 



robert d. rollo, PE 
Corporate Associate 
Parkhill, Smith & Cooper, Inc. 
Lubbock, Texas 
(806) 761-7539vox 
(806) 747-7146 fax