From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
Date: Mon, 24 May 1999 18:16:46 -0400
In the 1950's, 2,000 psi and 2,500 psi concrete was the commonly specified
concrete strengths. 3,000 psi concrete was *strong* concrete. *Very strong*
concrete was 3,750 psi (Yes, 3,750 psi; not 3,500 or 4,000, but 3,750 psi.
CRSI had a whole handbook based on 3,750 psi concrete.) Design working
stress was .45f'(c) in flexure.
You might want to get a couple of more cores from around where the 1260 psi
core came from to see if there was a batch of real low strength concrete
placed or whether this was a bad test.
A. Roger Turk, P.E.(Structural)
Steve Bian wrote:
. > 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.