Curing Concrete in Cold Weather
Curing concrete in cold weather requires knowledge, material and some of these tips. Snow, humidity, and water will prevent your concrete to settle down so you might want to be careful when pouring concrete and avoid it when the temperature drops below 20 F. Concrete hydration is affected when the temperature drops below zero F or freezing point. American Concrete Institute (ACI) Committee 301 recommends a minimum curing period corresponding to concrete attaining 70 percent of the specified compressive strength.
Materials Needed to Cure Concrete During Winter
Curing concrete in cold weather can be achieved using different materials depending on the amount of concrete being cured and the surface being protected. These materials when used properly will increase or produce a constant heat of hydration of the concrete. For example:
- Insulating sheets
- Heating coils
- Insulating blankets
If the temperature is below 20 F, simply abandon the idea of placing concrete because it will lead you nowhere as hydration stops completely at such temperatures.
For this reason, ACI Committee 308 recommends the following minimum curing periods:
- ASTM C 150 Type I cement 7 days
- ASTM C 150 Type II cement 10 days
- ASTM C 150 Type III cement 3 days
- ASTM C 150 Type IV or V cement 14 days
- ASTM C 595, C 845, C 1157 cements variable
Tips on How to Cure Concrete in Cold Weather
Try these recommended tips for curing concrete during winter:
- Maintain a proper water-cement ratio. The water to cement ratio should not be more than 0.40 under freezing conditions.
- If temperatures are too cold, a propane heater and polyethylene enclosure could be used to maintain temperatures hot enough, to avoid the freezing point.
- Use Portland cement Type III, cement that helps in setting without reducing concrete’s quality. It is important because high moisture content can induce corrosion problems in steel reinforcement.
- Control chloride ions by using fly ash, silica fume, and furnace slag.
- Leave forms in place as long as possible. Corners and edges are most vulnerable and forms will help during the heat release process.
- Removing the blankets suddenly in cold weather can cause a temperature differential to build up between the outside of the concrete and its middle. This can cause cracking from the thermal differential, but typically only in thicker members.
- Concrete underwater curing for flatwork applications becomes easy with pervious concrete. Pervious concrete is all coarse aggregates and it contains a negligible percentage of fine aggregates, especially sand. Additives are mixed into it that do not allow water to penetrate inside the concrete surface. Pervious concrete is suitable for constructing pavement as it does not soak in water but allows gallons of water pass through it without damaging concrete pavement and strength.
- Wait until all bleed water has evaporated. Curing concrete in cold weather will produce a slower curing procedure, so the concrete is setting slowly, and bleeding will also start later than expected. Be prepared to handle more bleed water than regular concrete placement.
- While concrete is being cured, verify the concrete temperature using an infrared temperature gun.
- To determine how much insulating value you need to keep the concrete at 50 F. The insulation needed is based on concrete thickness, cement content, and the lowest air temperature anticipated for the protection period.
- Seal concrete by applying concrete sealant so water does not seep into the concrete. Concrete sealants will extend concrete’s life and will reduce the concrete curing failure. In extremely cold regions, only a breathable concrete sealant must be used, as it will allow the evaporation of water and moisture, helping to speed up the setting of the concrete.