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RE: Concrete and rebar strength

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While the concrete may have been 2000 to 2500 psi at 28 days, it is probably now in the 5000 - 6000 psi range. Cements back then were a much coarser grind and took a long time to reach ultimate strength. Today we may only experience a 10-20% increase between 28 days and 1 year.

Jay Shilstone

At 03:23 PM 3/27/03 -0600, you wrote:
According to the 1929 Chicago Building Code, 1:2:4 concrete has a
compressive strength of 2000 psi. That is the closest I could get
(time-wise).

Eric Green

-----Original Message-----
From: Kestner, James W. [mailto:jkestner(--nospam--at)somervilleinc.com]
Sent: Thursday, March 27, 2003 9:46 AM
To: SEAINT
Subject: Concrete and rebar strength

I am adding loads to a building built in 1930. Amazingly, we have found
the existing drawings and specs!

There is no compressive strength specified for the concrete. However, it
specifies a concrete with 1 part cement, 2 parts sand and 4 parts
aggregate. Can I tell from this info., what the 28 day compressive
strength may be?

Also, the rebar is Federal spec. 350A, type B, any grade or class except
structural grade. Can I tell from this info. what the particular yield
strength is?

Jim K.

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