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Re: Mass concrete

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I was going to respond to this thread until I saw the name "Shilstone". For the uninitiated, Shilstone is one of the true guru's of concrete mix design.

Jay and Jim Shilstone before him probably know more about concrete mix design than anyone on the planet.

Thermal gradients can crack concrete quite easily. I am not sure what the function of the "pad" is, but if this is a foundation you need to ask if this should be a concern at all. Or can you place crack control joints to accommodate cracking. If cracking can not be tollerated, then you need to take actions in mix design, placing and curing to contol the heat of hydration and control the thermal gradient.

I would also look to the Bureau of Reclamation. They developed most of the rules for mass concrete used today.

Regards,
Harold Sprague



From: Jay Shilstone <j.s(--nospam--at)shilstone.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: Re: Mass concrete
Date: Wed, 04 Aug 2004 14:40:04 -0500

It doesn't matter whether it is called mass concrete or not. The question is, "Is there sufficient heat differential between the interior and exterior concrete temperatures to cause cracking?" If the mix involved has a high cement content, or has a high enough initial temperature, the answer is probably "Yes". When in doubt, treat it as mass concrete. You can either keep the internal concrete temperature as low as possible or insulate the whole deal to slow down heat loss.

We were involved in a project with 6 foot diameter columns cast with 5000 psi concrete. The concrete was cast in winter in Chicago. When the contractor stripped the forms 2 days later, the concrete rapidly formed alligator cracks all over.

If it looks like mass concrete and quacks like mass concrete, treat it like mass concrete.

Jay Shilstone

At 05:15 PM 8/3/2004, you wrote:
I have a concrete pad, approximate 3' to 3'-6" thick, 26' wide, 100' long. Is this considered a "mass concrete"? ACI 207 talked about the cooling of mass concrete etc. Most of the ACI mass concrete reports are related to dam construction. Is this pad "massive" enough to cause any serious heat problem?

Thanks for any input.

Y i   Y a n g,   P. E.
STRUCTURAL DIVISION
SUMMIT ENGINEERING INC.
707.527.0775.x15
Santa Rosa, California






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