When freshly poured concrete is exposed to freezing temperatures before it has set, the water within the concrete can freeze. This expansion disrupts the setting process, delays chemical reactions necessary for hardening, and increases the volume of pores within the hardened concrete, which weakens its overall structure. If the concrete manages to reach an appreciable strength before it freezes, the damage can be somewhat mitigated.
To counteract the negative impacts of cold weather, ensuring an adequate temperature of the concrete during and after placement is key. This is often achieved by using warm mixing water, heated aggregates, and modifying the mix with Type III cement or accelerators. This can also be done by insulating the concrete from the cold with thermal barriers, or actively heating the space around the concrete using methods like exhaust steam or jacket-like steel forms with circulating hot water.
Monitoring the concrete temperature with thermometers or thermocouples is essential, especially in strategic locations prone to rapid cooling, such as corners and exposed surfaces. Adjustments to insulation and heating may be necessary based on ongoing temperature assessments to accommodate sudden drops in ambient temperature.
