Knowing how to mix concrete for maximum effectiveness in cold weather is important for any ready-mix producer. According to ACI 306R-88, "Cold Weather Concreting," considerations include sand, aggregate, and mix water temperature; how mix ingredients are batched and the order in which they are added to the mixer; and anticipated temperature loss during delivery. Cold-weather mix modifications also are important to consider.
Mix water should be available at a temperature that is consistent throughout the day and in large enough quantities to avoid causing temperature fluctuations from one batch of concrete to the next. Temperature regulation is important for several reasons. The temperature of concrete affects the rate of slump loss and also may affect performance of admixtures. In addition, temperature fluctuation can cause variable behavior between individual batches of concrete.
When air temperatures are consistently below 25 Fahrenheit degrees, it is usually necessary to heat aggregate as well as water. This can be accomplished a number of ways including: circulating steam or dry hot air in pipes, fires in metal culverts, and steam jets.
Producers should also know how to calculate the following: temperature loss during delivery; special mix modifications for cold weather; and proper mix temperatures.