There’s an art to pouring concrete properly. While many think of this as summertime work, it is something that can be done year round—only, you’ll need to know all the factors that play into it in order to do quality work that won’t crack, become brittle or feature some other flaw. Where climate is concerned, there are six big factors that you’ll need to account for. These include air temperature, humidity level, wind speed, surface temperatures, water, and the dry concrete mix that you are using. Below, we’ll take an in-depth look at each of these to see how they affect things when mixing and pouring concrete.
1. Air Temperature
This one is the big one—and many advise against pouring concrete when temperatures dip below freezing. It’s true, too, that concrete shouldn’t be poured at all when the ground is frozen, and for a variety of reasons. Not just because it will affect the final product, but also because as the ground thaws, it will shift, which could crack the concrete.
Cold temperatures prove difficult because in order to speed up the setting process, the concrete will need to be heated somehow. Professionals usually start by using hot water to mix the concrete. For outdoor jobs, there are other alternatives, too, like heated tents in order to help it set.
At the opposite end of the spectrum, air temperatures over 90 degrees can pose problems, too. When the weather is hot, the top layer of concrete sets faster—and shrinks as it does so. This can result in cracking.
There are ways to prevent the top layer from drying too quickly—namely by keeping slabs wet so that they cure evenly. Some contractors will even use ice in the mix to help slow down setting times.
Humidity poses some of the same challenges as hot weather. When humidity is low, moisture evaporates from setting concrete more quickly, particularly from the top layer, which results in an uneven set that can lead to cracking. As with dealing with hot temperatures, the best solution is to keep the slab moist as it dries.
3. Wind Speed
This is another factor that has the same effect as both high temperatures and low humidity—and it’s worth mentioning because it’s a factor that isn’t often considered when pouring concrete. However, windy days will dry those top levels of concrete faster, resulting in a higher potential for cracks. When you combine a breezy day with low humidity and high temperatures, it becomes almost a triple threat, and keeping that top layer of concrete moist while the rest cures becomes imperative!
4. Surface Temperatures
Surface temperatures are important to the concrete curing process. While it is true that concrete can be poured most of the year, there is a “sweet spot,” which is when temperatures are between 40 to 60 degrees. Part of the reason for that is because these temperatures leave the ground’s surface at an ideal temperature for concrete curing. One of the important things to know about the curing process is that it’s comprised of not only water evaporating, but also chemical reactions—and temperatures that are too low slow these chemical reactions down, which can lead to weak, brittle concrete.
When mixing concrete, precision is key where adding water is concerned. Too little, of course, and the mix won’t moisten properly or pour well, but there are also dangers in using too much water. Not only will this result in a longer cure time, but more water also affects compaction. Basically, when using more water, grains within the aggregate are spaced farther apart—and when the concrete is cured, it won’t have the compressive strength or durability of concrete that was mixed with the correct amount of water. What happens is that all of the spaces which held water become voids filled with trapped air. Interestingly, levels of trapped air as low as 10% can cause a strength reduction of about 40%.
6. Concrete Mix
Mixture proportions are another key factor to consider. Cement is the primary adhesive in concrete—it’s what holds the aggregate and sand together. One might think that mixes with a higher proportion of cement might be better, but actually, this isn’t always true. Cement itself has weak tensile strength, which is what makes rebar a necessity to give concrete higher tensile strength. In general, it’s always best to look at different mixes carefully and choose one with the proportions that match not only the application, but climate concerns and any other challenges you may foresee.
While there are other factors to consider when pouring concrete—such as the likelihood that the ground beneath it may shift, for example, or the substrate on which it is poured—these six are the big ones that can really affect the strength of the final product. Take each in mind when pouring in order to ensure the concrete cures properly without cracks and other issues.