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heat curing concrete

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pmtrevisan

Structural
Apr 1, 2003
4
Hi all;
I have a question for the experts (as I am far from 1, still green engineer). Aside from the obvious creep/shrinkage cracking, are there any other problems with heat curing concrete. We regularly use propane heaters to heat cure our projects, and completely strip forms the next day (tunnelform technology - pouring walls and slab in one cycle).
We obviously get the required strength for stripping, and was wondering if anyone remembers the formula for calculating f'c for this situation (calculating concrete strength based on time, and the effect of heat curing)

Thanks in advance.

PMT B.Eng
 
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"Heat curing" is a misnomer. What you are doing is creating a warmer atmosphere for the concrete, thinking that this equates to "curing". The use of propane heaters is a protection measure from freezing and not a curing method.

You are potentially compromising the surface durability of the concrete by introducing early carbonation of the surface. Further, you are "drying" the concrete which leads to exacerbated shrinkage and larger cracks.

Provided the concrete is not exposed to freezing or near freezing temperatures, it should be wet cured or at the least the moisture in the concrete should be retained.

High temperatures during the initial curing stages will cause a reduction in ultimate strength of the concrete.
 
Good points, Ron, the carbonation aspect is often missed... This can cause some real 'dusting' problems with slabs, etc.

They often use 'heat curing' in the form of steam speed up the curing for regular and pretensioned precast. It reduces the time in the shop and frees up the molds for the next element.
 
Steam curing is a proper way to go. You warm up the concrete and add water in the form of vapor. And you don't introduce the CO and CO2 to the concrete surface. Check with your local manufacturer of precast beams and Tees.hey may be able to help you. A lot of the RCP pipe in the US is steam cured.
 
Using propane heaters to prevent the freezing of fresh concrete is certainly an accepted practice, if measures are taken to prevent the problems of premature drying and carbonization as noted above.

I seem to remember reading some specifications for winter concrete that called for X number of curing hours at Y degrees before stripping. If I find the reference I will post it.
 
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