Why You Should Cover Concrete in Cold Weather
Placing concrete in cold weather can be difficult. Concrete must reach a minimum strength of 500 psi (pounds per square inch), which happens within 24 hours at warm temperatures. When it’s cold, however, this can take much longer, or the concrete can freeze in a plastic state. A plastic freeze retards progress toward full strength and the minimum strength needed for further work to be safe.
One of the most straightforward solutions for this is curing blankets. The use of insulated curing blankets is simple, but with a variety of curing blankets on the market, which should you choose? We will discuss the options below.
Why Cure Your Concrete Carefully in the Cold?
Improper curing can lead to poor hydration, weak concrete, susceptibility to the freeze-thaw cycle, and eventual abrasion, scaling and spalling, both at depth and near the surface, for extended periods of time. Properly cured concrete has an adequate amount of moisture for continued hydration and development of strength, volume stability, resistance to freezing and thawing, and abrasion and scaling resistance.
Additionally, exposing concrete to the cold means it takes a lot longer to set. This can be expensive, especially on large projects with finishing crews who need to be kept on site.
Curing time depends on:
- Concrete design
- Strength needed
- Shape and size of concrete construction
- Actual ambient temperature
- Future exposure conditions
The American Concrete Institute recommends a curing period that allows concrete to reach 70% of the psi needed for your job. This can be up to seven days with some types of cement but is often 72 hours when other cement/admixtures are used or if temperatures are kept higher. For example, it takes almost twice as long to cure the same concrete at 50°F as it would at 70°F.
Why Choose Curing Blankets?
Blankets also help keep moisture in at the surface of your fresh concrete, which is necessary for reaching a "cured" level of strength. They’re waterproof, so they slow evaporation from below and keep snow, rain and ice from damaging your newly placed concrete.
Curing blankets are:
- Available in a variety of sizes and R-values
- Sometimes heated for extremely cold working conditions
- Easy to move and reuse
- Tough and durable
- Very easy to use
- A great value when compared to other options
So, how do curing blankets work? Let's have a look.
How Curing Blankets Work
Which Curing Blanket Is Best?
A more relevant question would probably be, which curing blankets are best for me? Or, which curing blankets are best for my upcoming construction projects? Every option has its upsides, so you will only find the perfect curing blanket if you take into account the likely weather conditions, the size of your project, and the makeup of your concrete, among other complication factors.
Types of Curing Blanket
- Polyester is the best value option for insulated curing blankets — although it’s tough, this multi-layered curing blanket will experience wear and tear in time from the sun. It provides a decent R-factor for cold temperatures by trapping warm air between layers of material.
- The other common option is closed-cell foam. This is seen as the best type of insulation, with trapped foam bubbles that stop heat and moisture from passing through the blanket and out into the environment.
- Foam blankets can also be layered. Like polyester blankets, they come in a variety of sizes, with three to six layers.
- Heated blankets are also available, though they are a more expensive option.
Planning for Curing Concrete in Cold Weather
Design your concrete with quick strengthening in mind — usually, this means more concrete in your mix. You can also warm the water in your concrete or use a heated mixer. The heat from the concrete will be trapped by your curing blankets, speeding up the curing process.
Usually, concrete will be cured in about 72 hours with the correct use of curing blankets.