How Long Should Concrete Cure Before Putting Weight on It?
Like cooking a chicken filet, not giving concrete enough time to cure is inevitably going to lead to problems. Rather than giving you salmonella, though, not giving concrete enough time to cure before putting weight on it will undermine its structural integrity, leading to lowered durability and a greater risk of cracking later on no matter how high the quality of concrete forms you use.
Oftentimes, the curing process is poorly understood by novice builders, leading to misunderstandings regarding how long it could take a batch of concrete to cure. So, let’s answer a few questions: how long does it take concrete to cure, how does the curing process work, and is there any way to make it cure faster?
How Long Does It Take for Concrete to Cure?
This is a tricky question, as the speed and effectiveness of curing rely on many outside factors to calculate accurately. Concrete cures in stages, getting progressively more durable as time goes on. These stages of curing should be kept in mind when determining how much weight it can take at any given time. Here are the average times:
- 24-48 hours: forms can be removed, can handle lightweight traffic (pedestrians, bicycles, wheelchairs, etc.)
- 7 days: vehicular and construction traffic is okay, but the concrete still hasn’t reached peak durability
- 28 days: concrete is fully cured and at peak durability
How Does the Curing Process Work?
The curing process strengthens the concrete in two key ways: retaining moisture in the slab to help the internal structures form, and preventing early damage that could be caused by drying shrinkage. Concrete is crystalline in structure, so if optimal time and conditions are provided for the crystals to grow, then the strength of the concrete will be optimal as well.
However, as said before, there are many factors that can affect the speed and effectiveness of the curing process. The main factor to keep in mind is what the climate is like around you. Like Goldilocks, concrete doesn’t like it when the temperature is too hot or too cold.
If the temperatures are too high, the concrete will dry and cure faster, but at a price: durability. Leaving your concrete to bake under the heat of a scathing summer sun may lead to cracks and overall weakness as the internal moisture is evaporated quicker than the internal crystals can form. The damage that excessive heat can cause is also why steam-cured concrete tends to be more brittle.
Conversely, if it’s too cold, concrete won’t set at all. Around 50°F, the curing process will slow down dramatically. At and below 40°F, it virtually stops. This is because, at these low temperatures, the crystals just won’t form at all. Some heat is required for the curing process to even begin, and if it isn’t applied, you’ll be left with a bunch of dry, uncured concrete. Just getting it initially set may take between 1-6 days, depending on just how frosty it is.
How to Cure Concrete Faster
So, now that it’s been made clear what the curing process is, as well as how long it might take under different conditions, it’s onto the final question: is there any way to make it go faster and still retain structural integrity? The answer is yes. Apart from temperature, there are other factors that can affect the curing process that are easier to control. Plus, even if the temperatures aren’t optimal, that doesn’t necessarily mean you won’t be able to properly cure it either. It’s all about picking the proper techniques for the job.
As stated, even though the temperature is important, sub-optimal temperatures don’t need to spell the end for your project. If it’s too hot, consider taking measures to ensure that your concrete stays moist throughout the curing process. This can be achieved by wrapping it in a plastic sheet to prevent excessive evaporation. You can also water the concrete as you would a plant, though you should be careful not to do this at the highest temperature, as this may cause thermal shock, which could cause cracks to form on the surface.
The process for cold concrete is much simpler: just warm it up. This can be accomplished by applying a good layer of insulation, some heating units, or even an enclosed space for the concrete to cure in. In some cases, a curing box may also be utilized.
Adding certain chemicals to your concrete prior to or during the mixing process can lead to a swifter curing process later on. Referred to as accelerating admixtures, adding these into your concrete early on can dramatically shorten the setting process, which in turn will allow the curing process to begin far sooner than it would without the aid of these chemicals. They also bolster the concrete’s cold resistance as a bonus, which might make them ideal for any cold weather projects you may have.
Common accelerating admixtures include:
- Calcium Formate. The most commonly-used accelerator and it typically comes in a powder form. It’s also used in dry bricking and stucco.
- Triethanolamine. An oily, water-soluble liquid that’s often described as having a “fishy” smell to it, this accelerator is much more difficult to utilize. Not only will it completely change properties if too much is used, but it’s also highly toxic to boot.
- Calcium Nitrite. Not as toxic as the former chemical and comes with the added bonuses of corrosion resistance and cold weather resistance. It often comes in an off-white powder.
- Calcium Nitrate. With much the same effects as its nitrite cousin, but it is also more water-soluble and slightly more toxic.
The Right Form Can Make a Difference
In any build, your foundations will always be the first priority. An insulated form could make all the difference in your project’s success. Here at Forming America, we offer top-quality concrete form rentals for projects of all shapes and sizes. It doesn’t matter what you’re building, where you’re building it, or how quickly you need it to cure—you can count on us to get your project started on the right path.