Working in Cold Conditions
Plan according to weather conditions
Provide a minimum/maximum thermometer on-site; this will determine the shade temperature and, if properly used, it will show if the temperature is rising or falling at a glance. Also, monitor local temperatures.
To avoid freezing conditions, plan work as far as possible in advance and ensure cold weather precautions are taken before temperatures reach freezing. Always work to shade temperatures as direct winter sunlight temperatures are not reliable. Also, take into account that the temperature may drop hugely after the sun sets.
Protecting stored materials
Provide covers to all materials that are susceptible to frost when work is to be carried out in cold weather. These precautions are to be taken in addition to the normal precautions outlined previously and will protect from overnight snow, ice, and frost as well as the effects of longer-term frosts permitting an earlier resumption of work.
To prevent the effects of overnight frost and saturation, waterproof coverings over bricks, blocks, sand, and ballast should always be provided in cold weather.
Longer periods of cold weather
During prolonged cold weather, provide extra protection to materials to be used during the progression of work and also protect completed work from the effects of frost.
Heaters should be used where required to prevent aggregates and other materials from freezing or frost occurring. Ensure that the use of heaters does not lead to materials drying too quickly or lead to shrinkage or cracking.
Avoiding damage to concrete as temperatures near freezing
In the case of foundation or oversite concrete:
Where the ground or hardcore is affected by snow, ice, frost etc. do not concrete foundations or oversite.
Precautions to keep the ground above freezing must be taken where work must take place during long periods of low temperatures.
Where work takes place on frozen ground, the work can become seriously damaged by movement due to the thawing of water. If ground or oversite becomes frozen, all work should be stopped. If work must take place, a cover may be erected and the area can be heated to create a frost free environment.
Concrete should only proceed in situations where the temperature has dropped to 2°C and is continuing to drop when:
The temperature of the aggregate is 2°C or greater and is free from snow/frost. And
The water used for mixing is heated. (<=60°C) And
Once cast the concrete is adequately protected.
Unless aggregates can be thawed, stop work if aggregates are frozen. Covering aggregates with a tarpaulin will not prevent severe frost from penetrating the aggregate; the use of hot air blowers or steam heat below covers may be necessary if work is to continue.
Heated mixing water
Heated mixing water cannot be relied on to thaw frozen aggregate as the water is only a small proportion of the overall volume, meaning that the aggregate can absorb all heat from the water while still remaining frozen.
Where the temperature has dropped to 2°C and is likely to keep dropping, work should be stopped on any job that may be affected by frost. Throughout the day, the temperature should be monitored.
Ready-mix concrete in freezing conditions
At the time of delivery, the temperature of the concrete must be 5°C or greater. Once cast, the concrete must be adequately protected. Where slight frost is expected, insulation secured at the sides will sufficiently protect oversite concrete. However, if the frost is expected to be severe, heaters may also be required.
To avoid damage to masonry, the following precautions should be taken:
Do not use materials susceptible to snow, ice, or frost damage.
Where the temperature drops to 2°C and is still dropping, cease work.
Work may continue if heat is provided under cover that will keep the masonry above freezing.