“The rule of thumb is that if the concrete can be kept above 40°F for 24 hours, it will reach design strength…
The reason insulation matters on cold-weather pours is because concrete hydration is exo-thermic.
That is, the chemical reaction between the water and cement actually creates heat.
The ICF provide insulation so that the heat generated by the curing concrete would keep itself above the 40°F threshold needed to ensure the designed strength is reached.”
Read more about conducted studies at https://www.icfmag.com/2013/11/cold-weather-concrete-pours/