Minimum Concrete Temperature

[Botto]

The engineer on our current project did not specify a minimum concrete temperature, the spec says to place concrete in accordance with ACI-301-05.

The answer is an easy one during the prescribed 'cold weather' but if we are not in cold weather concrete (1)is there a minimum temperature required and (2) how long are we required to maintain the temperature after placement?

This may seem as an odd question but it has been a great debate between our in house engineering and quality control department, any insight would be appreciated.

 

[Ron]

A minimum temperature is not often specified for the concrete. It is usually in the form of air temperature.

As a practical matter, you would like to see the concrete temperature not go below 40F. At about 39F, the density of water decreases and continues to decrease until it freezes. Further, long term performance of concrete with regard to temperature differential is affected. For instance, if you place the concrete while its temperature is 40F, it will expand more at common summer temperatures than it would if placed at, say, 60F...simply because the baseline temperature for thermal expansion is the temperature at the time of placement/setting.

 

[rscassar]

There was a concrete Q&A published in the December 2010 Concrete International that you should try and get a copy of.

My specification requires that placing concrete in cold whether be followed when temperatures are below 40F. Below 40F the concrete will not gain strength.

 

[concretemasonry]

Ron had a good point about the importance of the concrete temperature in contrast to the meaningless air temperature, which is easy to administer.

If you have the proper mix design, heated water, protected or heated aggregates and reasonable protection from the elements, the heat of hydration will over-rule the air temperature if the base the concrete is on is not too cold.

If you are in a cold climate, heated mixes should be available from a good supplier. We even poured concrete at -30F from a temporary plant with good aggregate storage. - Day before it was -42F, but we had 150 yards that had to be poured.




Engineer and international traveler interested in construction techniques, problems and proper design.

 

[concretemasonry]

Ron had a good point about the importance of the concrete temperature in contrast to the meaningless air temperature, which is easy to administer.

If you have the proper mix design, heated water, protected or heated aggregates and reasonable protection from the elements, the heat of hydration will over-rule the air temperature if the base the concrete is on is not too cold.

If you are in a cold climate, heated mixes should be available from a good supplier. We even poured concrete at -30F from a temporary plant with good aggregate storage. - Day before it was -42F, but we had 150 yards that had to be poured ASAP. The volume was nothing, but the batching and delivery were critical.




Engineer and international traveler interested in construction techniques, problems and proper design.

 

[concretemasonry]

Please ignore the first posting at 22:11, since it was not complete and I could not correct it after the fact. The 22:16 is corrected and intended.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[BigH]

So different from what we have to go through here . . . - cold, we would like cold . . . .

 

[henri2]

I am sure ASTM C94 is a referenced standard in ACI 301. ASTM C94 has a table for minimum concrete temperatures during cold weather concreting.