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Re: CONCRETE: Hot Base Plate Bearing on Concrete

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I had to research a similar situation a few years ago and the answers and recommendations are not all consistent.  The classical answer is 200 degree F since this is just below when the entrapped water will turn to steam which is what you will find in PCA, Design and Control of Concrete Mixtures.  ACI 349 goes as low as 150 degree F and 200 degree F for local areas at penetrations for long term exposure and 350 and 650 degree F for accidental or short term events.  I have three other papers that PCA sent me that all say there will be no appreciable damage for sustained temperatures up to 400 and 500 degree F.  Try contacting PCA as they were a great help to me.

Thomas Hunt, S.E.

Bill Polhemus <bill(--nospam--at)>
01/30/2008 12:12 PM
Please respond to seaint
CONCRETE: Hot Base Plate Bearing on Concrete

I have a "base ring" of a skirt-supported vessel. They have "changed" the insulation requirements on the thing which is expected to mean that the base ring will now get "pretty hot" on a cyclic basis (i.e. in an 18-hour cycle it will go from ambient to "very hot" back to ambient again; repeat ad infinitum).

They're asking me "how hot can the concrete stand?" They're working on the FEA for the heat flow now, so I don't have the temp yet, but I'm wondering for reference: how hot before we might have to worry? This is a very thick elevated slab - nominally six feet in thickness - with a large octagonal opening over which the equipment is situated; the closest the opening gets is a couple of feet from the ring.

I'm tempted to tell them to include the big chunk of concrete in their FEA, and tell me what the gradient(s) is/are.

Any comments?

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