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Re: Concrete Cure Time

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I tend to agree.  I normally recommend 7 days; three when pressed for "bare minimum." Anything less and I simply require a cylinder break at 2/3 of design strength. It's a kind of "put up or shut up" moment in most discussions. Some GCs are so cheap they'll wait the two extra days; others will write the check to the testers and go.

Harold Sprague wrote:
No code references.  It is an engineering judgment call.
It depends on what strength that you need.  I had a project in which I needed to place steel 24 hours from the concrete placement in the winter.  We developed a mix that did not need high early cement, but had a predicted strength of 2,500 psi in 24 hours.  I had extra cylinders cast and we popped one after 20 hours and got 2,700 psi and they started setting steel. 
It does not cost that much to get a better and earlier strength gain, and it often pays for the schedule compression.  This is done frequently in post tensioning and in slip forming. 
The first thing is you need to determine what you need.  What drives the 3 days you require?  Is it shrinkage control or strength gain dictating the requirement?  You can accommodate either with proper planning and mix design. 

Regards, Harold Sprague


From: RichardC(--nospam--at)
To: seaint(--nospam--at)
Date: Tue, 1 Sep 2009 11:11:03 -0400
Subject: Concrete Cure Time

Our residential clients have been pushing the time frame on when they can start running block after a slab pour.  Our standard has been 3 days.  However, some clients think this is too long, and we have recently found one placing block a mere 20hours after the pour…


So the questions has been brought up – what is the fastest time frame for block placement? Any code ref’s I can from here?


Richard Calvert, EIT 

Project Engineer


Lindemann Bentzon Bojack

Architects & Engineers

290 Citrus Tower Blvd, Suite 200, Clermont, Fl. 34711

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