Cold weather working

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Concrete shall not be placed in cold weather unless suitable precautions are taken.

The minimum temperature of ready-mixed concrete when delivered should be 5°C, in accordance with BS EN 206.

When concreting is undertaken during colder weather, curing periods should be adjusted according to environmental conditions. Concrete should:

  • be covered to maintain the temperature above freezing, and heated if necessary
  • not be placed where the ground, oversite or the surfaces that will be in contact with the concrete are frozen
  • be placed with caution where small quantities of fresh concrete are against a large volume of hardened concrete which is at a lower temperature.

Where slight overnight frosts are expected, 50mm of insulation held down firmly at the edges should be used to help protect oversite concrete. Where very severe frosts are expected, insulation alone is inadequate and heating should be provided.

Site-mixed concrete

If the air temperature drops to 2°C, concrete work should not proceed unless:

  • the ground into which the concrete is to be placed is not frozen
  • the aggregate temperature is above 2°C
  • the aggregate is free of frost and snow
  • the water for mixing is heated, but not above 60°C (cement should not be heated)
  • the cast concrete can be properly protected, taking account of the cross-sectional area and location.

In prolonged or very severe cold weather:

  • covers will not stop severe frost penetrating the aggregate
  • where work is to continue, it may be necessary to steam heat aggregates or to use hot air blowers below covers
  • heating the mixing water cannot be relied upon to thaw frozen aggregates, and very cold aggregate can still remain frozen.