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compressive strength testing on cored concrete -

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     Steve,
     
     For the early 1950's, 2500 psi concrete was probably not unusual.  In 
     fact I see 2500 psi and 3000 psi today in some of our client 
     specifications (personally I would not recommend it!).
     
     You also might check the core testing reports.  I assume you followed 
     ASTM C42 for the core testing.  If so, there are requirements for 
     length to diameter ratios and if you are outside these ratios you need 
     to apply correction factors.  There are also some "coefficients of 
     variation" you may need to apply.
     
     Thomas Hunt, S.E.
     Fluor Daniel


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Subject: compressive strength testing on cored concrete -
Author:  STEVE BIAN <sbian(--nospam--at)yahoo.com> at fdinet
Date:    5/21/99 11:36 AM


Hi, Fellows:
     
As part of an ongoing investigation of a water filtration plant built 
in 1953 (cast in place), three cores were taken for variety of tests 
from concrete walls of two filter cells. the result seems strange to 
me, pls help!
     
The half cell and chlorinde analysis deem there is minimum corrosion in 
the wall/rebar;
     
Petrograpic shows concrete is in fair condition with a 9/16 surface 
carbonation;
     
Visual inspection indicate about 1/8" pitting and wear due to chemicals 
in the water: chlorine, etc.
     
The compressive test, strangely shows really low compressive strength 
of the three cores: 2520 & 2410 psi respectively on two cores from one 
cell and only 1260 psi from another cell!!!!!
     
For pour in place concrete, these strength is really low although I did 
not find the design strength on record drawings. I did expect minimum 
3,500 psi - 4000 psi for this structural concrete.
     
Does any of you have such experience to justify such low testign 
result? 
     
I intend to do a Windsor Probe (ASTM C803) to test on site again. Do 
you have any comments and recommendation?
     
TKS in advance
     
     
Steve Bian, PE