Concrete can be difficult to work with, even in the best weather. In cold weather, it needs more preparation, more attention, and special precautions come into play. But you can’t slow down and wait for the warm spring days to return. You’ve got a schedule to stick to, and your customer needs the work done. You’ve also got to provide a quality outcome – there’s no excuse for poor workmanship. So how do you deal with concrete when the mercury starts dropping?
Concrete Problems in Cold Weather
When we talk about cold, we talk about steady temperatures at or below 40° Fahrenheit for at least three days in a row. When this happens, the concrete itself lowers in temperature. When the mixture starts getting cold, two distinct issues pop up.
The first issue is the freezing of the water within the mix. When concrete freezes, it breaks up the matrix, weakening the concrete itself. The key is getting your concrete to 500 PSI. That’s the point when hydration of the cement has consumed most of the water in the mix, meaning that there is not enough water left to cause damage even if it should freeze.
Secondly, it takes concrete longer to set when it is cold. Below 50° Fahrenheit, the hydration reaction that is necessary for concrete to set slows, and when the concrete hits 40° Fahrenheit, the reaction stops. It must be noted, this relates to the temperature of the concrete, not the air temperature. However, low air temperature will lead the concrete to cool quicker, and to rapidly approach the critical temperature points.
Solving the Problems
There’s plenty you can do that can help to avoid issues and concrete failures, even while pouring in cold weather.
- Never Pour Concrete on Frozen Ground: If you pour concrete on frozen ground, when the ground thaws, the ground will settle under the weight of the concrete, and it won’t be even – some places will settle further or faster, leading to cracking and fracturing of the concrete. The contact with the frozen ground can also slow the curing process, leaving the lowest layers soft long after the top sets.
- Just Like with People, Layers Are Best: By using concrete blankets and providing the concrete with a layer (or layers) of protection, wind chill and dropping air temperatures can be separated from the concrete, which can retain its temperature. Enclosing the pour site to keep temperatures at bay is a good idea as well – a simple tarped structure can be more than enough to help your workers and your concrete endure the cold.
- Use Insulated Forms: Most concrete forms are cardboard or wood – not the best materials for keeping the cold away. By using insulated forms, built to withstand the cold weather and keep temperatures warmer, you can prevent the concrete from curing unevenly for freezing around the edges.
- Heaters Can Help: Forced air torpedo heaters are the perfect tool to keep concrete warm, by circulating hot air and pushing cold air away. This is most effective in an enclosed area where the heat isn’t coming and going, but can be kept at a reasonable temperature. These heaters can keep an enclosed structure above the 40° step around the clock, ensuring the concrete has the opportunity to cure as it should. These can also be used before pouring concrete to prevent ground freezing. One word of caution – fossil-fueled heaters can interact with the concrete, and if the area is not properly ventilated to allow fumes to escape, carbonation in the concrete creates the dusting effect.
- Heating the Concrete Too: Heating coils and heating cables are sometimes used to speed up the concrete curing process even in warm weather, and they have the same application here. By heating the concrete and encouraging faster curing, you can avoid the issues that come from low curing temperatures.
- Change the Make-Up of the Concrete: Switching up the mix of the concrete in preparation for pouring can help to mitigate the cold weather. Using air-entrained concrete, placing the concrete at the lowest practical slump, utilizing hotter water when the concrete is being mixed at the plant, adding accelerators, and even adding extra cement or a higher-strength, rapidly-hydrating cement to the mix can all improve performance during pouring and curing.
Not Just the Concrete
It’s not only the materials that take a beating in the colder months. Your employees and your tools can also be stressed in the colder weather, leading to poor performance and poor outcomes. This can be easily solved or avoided through a few minor actions.
- Make sure your employees are protected with the appropriate cold weather gear, from parkas, bombers, and gloves to hard liners and hand warmers.
- Keep your forms and tools warm – if they are cold when they come in contact with the concrete, it can cause unevenness across the project, with spot issues even if you have followed all the other precautions.
- The heaters mentioned above? They don’t just help out the concrete, they also help to keep workers and tools warm. Having your team work in relative comfort, with trustworthy tools, helps to reduce the chance for issues to crop up or poor workmanship.
- Provide heated break areas and warm beverages for your workers – getting a fifteen-minute break in a warm trailer and a cup of tea or coffee can help them to refocus and revitalize, preventing distractions that can come with cold temperatures.
- Lead safety talks regarding cold-weather hazards and how to avoid cold stress or exposure.
Cold weather concreting is nothing to be scared of, and you shouldn’t let a few days of sub-freezing temperatures stand in the way of your concrete project. By modifying the concrete, the microenvironment around the concrete, and by paying attention to your workers and their tools, you can create the perfect environment for project success, no matter how cold the air temperature gets. Our team at PowerPak can help you fit out your organization and teams to be well-equipped to continue successful performance on concrete projects through even the coldest months, reach out to us today!
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