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Heating concrete using hot water

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:

t_m = [0.22(t_a m_a + t_c m_c) + (t_w m_w)] / [0.22(m_a + m_c) + m_w]

where

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 50^oC will result in a rise in concrete temperature of approximately 10-15^oC.

The temperature of the water added should be no more than 60-80^oC 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 finished concrete should also be protected from the cold environment e.g. by covering with frost blankets or other insulation.

Acknowledgement: The Concrete Society

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Concrete on site 11: Winter working