Cold-weather concreting: what should be checked on site?
- Published
- August 8, 2026
- Reading time
- 2 min
- sections
- 4
Short answer
Fresh-concrete temperature must stay above the specified minimum and the concrete must be protected from freezing until it develops sufficient strength.
- Hydration slows as temperature falls and drops markedly below 5°C.
- Freezing before sufficient strength develops causes permanent damage.
- High-early-strength cement can be advantageous in winter.
- Formwork stripping should be based on measured strength, not the calendar.
Temperature is as important as mix design in concrete placement. As temperature falls, cement hydration slows; a mix reaching a given strength in three summer days may not reach it in a winter week. The main risk is not delay but freezing before strength develops.
Why early freezing causes permanent damage
Free water in fresh concrete expands when it freezes. If the concrete is not yet strong enough to resist that expansion, its internal structure is damaged. The resulting voids remain after thawing, leaving permanent scaling, strength loss and increased permeability. Later curing cannot reverse this damage.
Measures before placing
- Remove snow and ice from aggregate stockpiles; do not use frozen aggregate.
- Heat mixing water as required to keep fresh concrete in the target range.
- Clear ice from formwork and reinforcement before placement.
- Check that the subgrade is not frozen.
- Avoid scheduling the pour during the coldest part of the day.
Cement and mix design
High-early-strength cement offers two winter benefits: useful strength develops sooner and additional hydration heat helps the concrete retain temperature. By contrast, high slag or fly-ash contents react much more slowly in the cold and may need adjustment for winter work.
Lowering the water-to-binder ratio reduces the amount of free water that can freeze. Accelerating admixtures may be used, but chloride-bearing accelerators should be avoided in reinforced concrete.
Curing after placement
Winter curing focuses on retaining heat as well as moisture. Cover the surface with insulating blankets and do not remove formwork too early. Formwork acts as a thermal shell; early removal causes heat loss and a sudden surface-temperature drop.
Deciding when to strip formwork
Stripping time should be based on actual strength measured using field-cured specimens or a maturity method. A period sufficient in summer may need to be doubled in winter.
For projects with a winter programme, cement type, strength class and curing plan should be designed together. Our technical team can recommend a solution for the specific site conditions.
Frequently asked questions
Below what temperature should concrete not be poured?
There is no single universal cut-off. Fresh concrete must remain above the project minimum and be protected from freezing until adequate strength develops. Colder conditions require progressively stronger controls.
How much can mixing water be heated?
Water may be heated, but very hot water must not contact cement directly because it can cause flash setting. It is normally blended with aggregate before cement is added, while fresh-concrete temperature is kept within the target range.
Can automotive antifreeze be used in concrete?
No. Concrete uses purpose-designed accelerating or anti-freezing admixtures. Automotive antifreeze is unsuitable, and chloride-containing products should not be used in reinforced concrete because of corrosion risk.
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