Triggered review of Concrete for Engineers course materials (from 1982, so practice may have evolved!).
- Temperature of concrete should be kept above 0 C at all times
- The water and/or the course aggregate may be heated in the concrete batching process to prevent freezing during transport and at point of placing into formwork
- Heat dissipates through unprotected surfaces and un-insulated formwork, so forms may have added insulation and open surfaces should be closed off with tarps or insulation
- Curing cement generates heat within the concrete, counteracting heat lost to the environment
- Concrete strength develops more quickly at higher temperatures
- Temperature of concrete shouldn't exceed 80 C during curing otherwise design strength will never be achieved
- Too steep a temperature gradient through the body of the concrete before it develops early strength will cause cracks to form, so external heating can be provided - but not so much that the internal temperature exceeds 80 C.
- Water loss can also prevent development of concrete strength and is related to the temperature difference between the air and the concrete, to wind speed, and to relative humidity of the air. So, exposed surfaces should be protected from the wind, particularly on cold, dry, windy days.
Are calculations being made in the site office before each winter pour or are a a set of standard practices being applied, I don't know. Perhaps someone with first hand knowledge of current practices can comment.
