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Heading: 1.1.1Cement Temperature
Message:
What is the maximum cement temperature at delivery that should be accepted?

At this temperature what effects can I expect in the concrete (not including, hotter concrete) and what should be done to counter-act these effects.

Thanks

Peter


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Peter Schwenger


The Portland Cement Association did an exhaustive study on this and the net result was that higher cement temperatures caused no meaningful problems other than to increase the concrete temperature. In the hot summer months, hot materials regardless whether they are cement, stone, sand or water will elevate concrete temperatures where it may become difficult to meet concrete temperature ceilings called for in project specifications. This may mean that a producer will need to sprinkle stockpiles to keep aggregate temperatures down. He may need to add ice as a partial replacement of some of his mix water. The most important factor is not the cement temperature but the concrete temperature. High concrete temperatures lead to lower strengths, slump loss, adding water on jobsites, increased shrinkage, higher potential for cracking, etc. Some contractors pour early morning to avoid high ambient temperatures in the PM.


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Fred Croen


Concrete temp is the determining factor, and cement hydration, in and of itself, produces chemical heat. Higher starting cement temps only exacerbate this action. I have had personal experience with high temp cement. In thick section concrete, the seven day breaks were in excess of 5,000 psi for 5.5 bag, natural aggregate, 2” slump concrete, with cement temps in the 180f + range. The 28 day breaks did not gain more than 10%. The solution was finding cooler cement. Hot concrete can cause hydration cracks as the concrete cools, and other problems.

I have also witnessed the effect of flash setting of concrete in the truck mixer. The appearance of the concrete is normal, but the 7, 14, 28, and 56 day breaks all failed. This was determined to be caused by flash setting due to excessively hot cement. This is particularly dangerous as results are not known for at least 7 days, and often 28 days.

There are many other factors that affect concrete temp, but they are too numerous to list here. The simple solution is a specification that calls for the maximum temp of the cement at the time of delivery to 105 F. That at least eliminates one of the factors contributing to higher concrete temps.

Bill Mangum


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Bill mangum Mangum
 
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