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Subject: Reinforced concrete base for Lehman instrument
From: beezaur beezaur@..........
Date: Fri, 07 Mar 2003 11:43:03 -0800


I am preparing to build a Lehman type seismograph and was wondering 
about materials for the base.  I am considering a slab of reinforced 
concrete (R/C) about 20" by 40" max, but coffin-shaped, say 3-4" thick 
and ~120 lbs @ 150 pcf.  This is similar to the stuff parking garage 
floors are made of.  It is a very stable material and can be cast to 
include mounting points for various hardware.

I have read about the unreinforced recipee 1:1 sand:cement for piers, 
but this does not give the bending strength required for my slab.  I am 
thinking of a more conventional mix using ~1:2:3 cement:sand:pea gravel 
and a lot of small reinforcement (#3 bar or welded wire fabric).  If I 
vibrate it well, I should be able to avoid air pockets.

My main concern is thermally induced noise from reinforcement 
expanding/contracting differently than concrete.

Has anyone done or heard about this?  Do you think it would produce 
internal noise?

Scott P
A day without math is like a day without sunshine.


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