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compressive strength testing on cored concrete -

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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
CCJM
Washinton, DC

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