It is important to know what the ambient temperature is when you are pouring concrete as it needs to have the correct temperature while it is curing, a process that can take anywhere between 3 and 7 days. When it gets very cold, concrete must have a heated enclosure or something a construction heater that prevent it from freezing. When it is hot, sunshades and windbreakers can retard evaporation, while certain retarders can be applied to the surface of the concrete for the same purpose.
Concrete is best poured when temperatures range from 40° to 60° Fahrenheit. When temperatures go below this, the chemical reactions that give strength to concrete can slow down and lead to the weakening of the concrete. When temperatures go below the freezing point, this can lead water inside the concrete freezing and the resulting expansion of the water causing cracks in the concrete. Concrete requires to set before it is exposed to any low temperatures.
What can you do, if you have to pour concrete during cold weather, and what precautions to you need to take during the period when the concrete is being cured? The ground on which you are storing pouring the concrete needs to be thawed with heaters. See that the materials used for making the concrete are in a place that is warm and dry, and even covered with insulated blankets to ensure this. Warm or hot water can be used for the water that is being used to make the concrete.
Concrete will bleed when it is freshly poured, and during initial set, this water must be removed with vacuum or squeegees, so that it does not freeze over. The use of concrete that has low slump can help to reduce this bleed water. If the mix is not heated, extra cement needs to be added to the concrete. so that it gains strength early. Finishing must only be started after the bleed water is removed, and must be done with great care. It is important that a constant watch be kept over the concrete surface, so that ice is never allowed to form on it. If the ice forms, it will lead to a stoppage of the process of hydration, and this can seriously affect the development of its strength. If fresh concrete freezes during the first twenty four hours, it will lose a substantial part of its 28 day strength.
During the curing period, it is important to use insulated blankets to cover the concrete, or enclose it in an enclosure that is heated. Concrete releases heat due to the chemical reactions when it is being cured, and it is this heat that needs to be trapped and made use of. This should be done for at least three to seven days. It should result in temperatures of the concrete being maintained at at least 50°F. If heaters are being used, it may be advisable to add additional water for the curing to prevent it drying out. The use of a good curing compound for at least three to seven days can also achieve this same result. Even after the blankets or enclosure is removed, concrete temperatures need to be maintained above 40°F for at least four more days. Removal of the heat protection must be gradual so that the concrete is not shocked into becoming cold in freezing weather. Insulated formwork can also help in preserving the heat from the concrete while it is curing.
It is important the when you have poured concrete during cold and freezing weather, that the the concrete temperature be constantly monitored to maintain it in the range of 40° to 55°F. Infrared thermometers can measure the surface temperature of the concrete, while sensors can be used for its internal temperature.