Forum Message

Heading: Temperature
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.



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.

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

Bill mangum Mangum

I would say that in the hot summer months, when cement demand is high, it may not be possible for suppliers to maintain a maximum cement temperature at time of shipping below 105F. That could be difficult even if the cement supplier has a million dollar cooler installed at their facility. I think the normal expected range would be up to 160F. No strength gain from 7 days to 28 days is a function of the chemistry of the cement C2S vs C3S and of the initial curing temperatures of the cylinders being used to test the concrete. They do make field curing chambers that will maintain 73 (+-)4F and 100% relative humidity. We use these in the field when situations warrant.

Fred Croen
Keystone Cement
Fred Croen

I agree with Bill that it is the concrete temperature that is most important – refer ACI 305R for the reasons. However, a high cement temperature contributes only minimally to a higher concrete temperature. The simple reasons for this is that concrete mixtures contain only about 10 to 15% cement, and the specific heat of cement is similar to the specific heat of the major constituents of the mix, i.e. the aggregates.

Clause 2.5.1 of ACI 305 states, “Cement may be delivered at relatively high temperatures ……. This will increase concrete temperatures approx 1F (0.5C) for each 8F (4C) increase in cement temperature.

The increase in concrete temperature can be compensated for by a much smaller decrease in temperature of the water added to a mix, as the specific heat of water is four to five times that of the cement and aggregate. Refer the heat balance equations in Appendix A of ACI 305R, or Figure 2.4.4.

Alan Kirby.
Alan Kirby
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