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?
As mentioned above, concrete has to be protected until it reaches 500 psi. At this point, you will be able to walk on the partially cured concrete, and it will be able to withstand a freeze-thaw cycle. In addition, when concrete has been placed and finished, it must be cured. That is, moisture and temperature conditions should be kept steady both on the surface of the concrete and deep within it.
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?
Thermal curing blankets are by far the least expensive option for speeding up concrete curing and protecting freshly placed concrete from exposure to the cold. Curing blankets can be used instead of enclosures and heating your concrete mixture, or in addition to these measures.
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
Curing blankets deliver R-factor, otherwise known as thermal resistance. R-factor is a measure of how well a material resists heat flow. So, a higher R-factor (or value) means more resistance — aka heat won’t escape quickly or easily when covered by a high R-factor blanket. The U-factor (or U-value) is the mathematical opposite of the R-value, measuring how well heat flows through a material. So, a very insulated blanket will have a high R-factor and a low U-factor.
R-value is the rating system used to grade insulation products or a material's insulating properties. The “R” stands for “resistance” and refers to a material's resistance to heat flow or temperature conduction. When a product or home has a high R-value, this means it is well insulated.
Using curing blankets is extremely easy. After finishing, you simply lay them on top of the concrete, ensuring no concrete is exposed. Usually, a single blanket offers enough insulation, but this depends on the R-value of the material, the air temperature, the ground temperature, and the temperature of your concrete mixture. You will need to measure these three temperatures (using a temperature gun) to ensure your blankets provide enough insulation and work out how long to leave your curing blankets covering the concrete.
You should use more blankets at the edges and corners of fresh concrete floors and bases. This is where most heat loss will occur, as it is in direct contact with the earth. If you have thicker blankets, place them here. Otherwise, stack blankets on top of one another.
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.
Heated blankets can be used in extreme cold to both warm and insulate your concrete. Additionally, heated blankets, which have a heated wire running through them, can be used to warm the ground before you place concrete.
For best results, plan ahead for curing concrete. If you know it will be cold, you can insulate the newly excavated earth you will be placing concrete on to keep in subsoil heat, for example.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.
Why White Cap
White Cap has 35+ years of experience in the building industry. Our experts worked in construction before joining the White Cap family and can answer any questions you have about curing blankets and cold-weather concrete projects. Work with a knowledgeable local White Cap representative to determine exactly what you need for your next job, right down to the R-value of your blankets.
We offer delivery and two-hour will-call service to keep you on track at the job site, even in fast-changing weather conditions.
And while you’re picking up the perfect curing blankets, don’t forget other cold-weather essentials. We carry everything from gloves and hand warmers to generators and lighting.
