Every spring and fall we as a ready mix producer are asked when are we going to start heating or when are we going to stop heating. Our goal is to always maintain a temperature above 50° F, and to do so requires a number of steps. The easiest is to heat water, but to only do that can cause problems with how the concrete holds slump and sets when the aggregate get too cold. When that becomes a problem we must heat the aggregate before we introduce the water and cement, which we do with the use of steam. Heating the aggregate makes for a much more uniform concrete from batch to batch and solves any issues that could arise from frozen chunks of aggregate in the mix.
As the temperatures go up in the spring it still takes a while to get the frost out of the ground. It takes a similar amount of time to get the frost out of our aggregate. If we stop using steam or hot water too early the result will be very slow setting concrete or worse, concrete that sets out of sequence. We always like to see concrete set from the bottom up, but when you put cold concrete on a cold sub grade on a warm spring day the exact opposite happens. Above are examples of different scenarios of how different materials affect the temperature of concrete. Remembering that even though it may be 65° outside for a day or so our stock piles take much longer to warm up. If you would like a complete chart of Predicted Concrete Temperature examples please email me at firstname.lastname@example.org.