When is It Too Cold to Pour Concrete

Temperature is a key factor when you’re pouring concrete. As temperatures fall, the curing process slows down significantly, which can cause major delays in your construction project. Further, concrete that’s cured at low temperatures is weaker and more likely to crack than concrete that cures in warmer conditions. Our Florida-based team at U.S. Pave has written this guide to understanding the complexities of cold weather concrete jobs to help you get the best results possible in these tricky conditions.

The Ideal Temperatures for Pouring Concrete

The ideal temperature for pouring concrete is 55 degrees Fahrenheit. If you can’t maintain this optimal temperature, an appropriate concrete curing temperature range may fall anywhere between 50 and 60 degrees Fahrenheit. It’s better to opt for warmer temperatures than cooler ones. In extreme situations, concrete can cure successfully at temperatures up to 90 degrees Fahrenheit. Concrete cured at 50 degrees Fahrenheit often outperforms concrete cured at 90 degrees Fahrenheit measurably.

Though it may seem like concrete simply dries and hardens, there’s actually a complex chemical process taking place within this substance. Concrete is a mixture of cement powder, water, and aggregates such as sand, gravel, or crushed stone. When the cement powder comes into contact with water, cement hydrates form on the surface. The cement hydrates gradually expand and interlock with other surfaces and each other.

The concrete stays in a plastic state while the cement silicates dissolve into calcium and hydroxyl ions. Eventually, the calcium-silicate-hydrate gel and calcium hydroxide become strong enough to break into the hardening stage. At this point, the cement dissolves and new compounds form that mesh together into a compound that gradually increases in strength while decreasing in permeability.

If this process doesn’t take place at the optimal temperature, the quality and strength of the concrete are compromised. The resulting product will be prone to cracking and suffer from reduced durability and a shorter life span.

How Cold Impacts Wet Concrete

The effects of cold weather on concrete are immediately noticeable. Concrete takes significantly longer to harden when poured at temperatures below 50 degrees Fahrenheit. Below 40 degrees Fahrenheit, concrete will struggle to harden at all, and at temperatures below freezing, it’s impossible for concrete to cure.

The minimum temperature for pouring concrete is always 50 degrees Fahrenheit. Anything below this will cause irreversible damage to the mixture, resulting in a weaker finished product even after the concrete has warmed and cured. If you allow concrete to freeze within 24 hours of the initial pour, it can lose as much as 50% of its 28-day strength. If the concrete freezes and thaws throughout the curing process, it’ll be continually shrinking and expanding with the changing temperatures. This results in unsightly cracks in the finished product.

Curing a concrete surface at cold temperatures can result in it developing a weak surface skin leaving it prone to scaling. Scaling occurs when the surface of the concrete flakes off and is the result of repeated exposure to the freezing and thawing cycle. Though any concrete surface may eventually scale for several winters, concrete that’s cured in freezing or near-freezing temperatures will do so much sooner and on a larger scale.

How To Protect Concrete in the Cold

You’ll need to use special concrete curing techniques in cold weather to protect the concrete from surrounding temperatures. The concrete needs to stay over 50 degrees Fahrenheit for the first three to seven days after pouring and over 40 degrees Fahrenheit for the next four days after that. If you know that you’ll be pouring your concrete in conditions below 50 degrees Fahrenheit, you can take proactive measures to keep your materials and tools warm such as:

• Thawing the ground with heaters.
• Mixing the cement with hot water.
• Using a quick-set concrete mixture.
• Mixing a larger batch of cement to increase the temperature from the chemical reaction.

Here are some other ways to protect concrete in the cold:

Heating Systems

If you can construct an enclosure over your concrete, you may be able to use a heating system to keep the area at the proper temperature. This is the ideal option for cold-weather concrete jobs, but it’s not always feasible. Make sure the enclosure is windproof and waterproof. Provide good ventilation throughout the space so the extra carbon dioxide created by the heater has a safe way to escape.

Insulating Blankets

Insulating blankets in a framework around the work area can provide some concrete protection in winter. These are a versatile choice you can implement in nearly any job site. Place a layer of plastic over the surface of the concrete, and cover the plastic with insulating blankets to seal in warmth. Wait until the concrete has completely dried to remove any framework you’ve constructed around the concrete. If you remove the framework too early, the surface of the concrete may collapse.

Admixtures

Admixtures are extra ingredients that you incorporate into the concrete along with the cement, water, and aggregates. They’re a good choice for proactively addressing cold weather. You may need to combine admixtures with insulating blankets or heaters if the concrete temperature is still too low. In cold weather, you may want to use admixtures such as:

• Accelerators: An accelerator such as calcium chloride increases the rate of hydration so the concrete cures faster.
• Air entraining agents: These additives create small air bubbles within the concrete that make it more resilient to the effects of freezing and thawing. The bubbles provide room for the concrete to expand as it gets colder, minimizing the risk of cracks.

Monitoring and Maintaining the Temperature of Concrete

Always practice proper temperature monitoring in concrete construction. Thermocouples for concrete curing provide a reliable way to monitor the core temperature of the concrete throughout the curing process. These temperature sensors measure the temperature at a frequency ranging from every 10 minutes to once an hour and typically work for several days. With thermocouple temperature sensors in the concrete, you can accurately adjust your heating measures to maintain the appropriate temperature.

Get Expert Guidance on Your Concrete Projects

It’s crucial to adhere to the industry’s best practices for concrete pouring in cold temperatures. Utilizing the proper measures will help you achieve long-lasting and structurally sound concrete structures. Our expert team based in the Fort Lauderdale, West Palm Beach, and Tampa areas of Florida, is ready to help with all your concrete paving needs. Contact U.S. Pave for expert guidance and assistance in managing concrete projects during cold weather seasons.

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