In cold weather, it may be an advantage to raise the temperature of the fresh concrete at the batching plant so that the concrete retains a sufficient temperature to promote setting and strength development to off-set the risk damage caused by early age freezing. Heating the mixing water is the simple way to warm the fresh concrete.
The following can be used to estimate the temperature requirements:
tm = [0.22(ta ma + tc mc) + (tw mw)] / [0.22(ma + mc) + mw]
t = temperature (oC)
m = mass of component per unit volume
Suffixes m, c, a, w refer to concrete, cement, aggregate and water components respectively
Alternatively, the following may be used for on-site mixing as an estimate:
An increase in water temperature of 50oC will result in a rise in concrete temperature of approximately 10-15oC.
The temperature of the water added should be no more than 60-80oC to prevent cement flash setting and reduce risk of scalding. Also, it is important to feed the mixer in such an order to prevent cement coming into direct contact with the hot water which may lead to cement balling.
Obviously the placed and finish concrete should also be protected from the cold environment e.g. by covering with frost blankets or other insulation.