Concrete Curing 101
An In-Depth Look at the Concrete Curing Process
Concrete curing is an important and necessary part of any concrete project. How well you cure concrete will determine its final strength and quality.
Aside from the curing process, the strength of concrete is also dependent on its mix. So to make sure you have the proper strength of concrete for your project, consult with ready mix concrete companies.
Here’s a look at what concrete curing means and how you can do it properly to ensure you have a strong, durable, and lasting concrete for any concrete project, large or small.
What Is Concrete Curing?
Concrete curing is the process of keeping freshly poured concrete from drying out too quickly. Once poured, concrete requires adequate moisture, temperature, and time to cure properly.
Curing allows concrete enough moisture to gain strength over time. And it delays drying shrinkage until the concrete is strong enough to withstand shrinkage without cracking.
Why Is Curing So Important?
Without curing, concrete will dry out before a strong bond forms between all its ingredients. As concrete hardens, its water content rises to the surface.
If this water evaporates too quickly, it can cause both large and small cracks to develop in the concrete. It may also cause crazing—fine cracks that spider web across the concrete surface.
This results in a weaker concrete with a surface that won’t be strong enough to support the weight for its purpose—e.g. vehicles in a driveway, or patio furniture.
Concrete that doesn’t cure properly is also at risk of developing a weak, dusty, and crumbling surface, similar to chalk.
How Do You Cure Concrete?
You can cure concrete using several methods. But no matter the method you choose, make sure to leave the concrete forms in place to stop concrete from drying too quickly and to help with the curing process.
This method involves flooding, ponding, or misting concrete with water. It is considered the most effective curing method to prevent water from evaporating from the concrete mix too quickly.
To flood or pond water on concrete, form a dam wall of sand around the concrete formation, and use a hose to flood water on top.
A simpler way of water curing is to spray water onto the concrete slab with a hose or sprinklers.
To retain moisture in concrete, you can use wet coverings such as sand, straw, canvas, or burlap. These materials must be kept wet during the curing process—e.g. with a sprinkler or a hose. If left to dry, they may aid in sucking out moisture from the concrete.
During high temperatures, you should cover concrete with wet burlap or a curing blanket and keep the cover constantly wet. This will prevent concrete from losing too much water from evaporation.
In colder temperatures, you can keep concrete warm with a burlap or straw covering. This will prevent the concrete’s water from freezing, expanding, and cracking the concrete.
Waterproof Paper or Plastic
These materials can be used once concrete is hard enough to resist surface damage. But plastic film can cause discolouration, so do not use it if the appearance of concrete is important.
You can also use a plastic sheet, held down with timber or cement blocks. Before placing any of these covers on the concrete, make sure to spray water on the concrete slab with a hose.
If using curing chemicals, such as compounds or oils, you must apply these to concrete immediately after you finish the concrete.
Some compounds, like soluble waxy emulsions, can be sprayed onto concrete and left for weeks until they break down in the sunlight.
Note that some curing compounds may affect the adherence of resilient flooring, so speak with a concrete company before using these.
How Long Does It Take for A Concrete Slab to Cure?
At the very least, you should keep a concrete slab wet and warm—at temperatures between 10 and 32 degrees Celsius—for the first week. But ideally, you should let it cure for 28 days.
Concrete doesn’t reach its full potential strength until 28 days after pouring. So the longer you allow concrete to cure while keeping it wet, the harder and stronger it will become.
How Strong Is Cured Concrete?
The compressive strength of concrete is referred to as concrete cube strength or concrete cylinder strength and is measured in psi (pound-force per square inch).
The strength of cured concrete will depend on the type of mix you use. And this mix will depend on the type of concrete project.
If you’re pouring a concrete driveway, the mix should have a minimum compressive strength of 4000 psi to support the weight of vehicles.
As concrete cures, it gains strength. After 28 days, concrete gains 99 percent of its strength. And concrete may continue to gain the remainder of its strength for up to a year or two after.
You should keep heavy equipment off of concrete for the first 28 days while it’s strengthening. And you should definitely not walk on concrete for at least three days after pouring.
What’s the Difference Between Setting and Curing Concrete?
Concrete is set when it has hardened enough to support some pressure without being damaged—e.g. when you can walk on a concrete slab without leaving footprints.
Concrete is cured when it reaches its full strength. Once concrete is cured, it should be able to support the weight it was designed to support.
Depending on the conditions, concrete can set in less than two hours and up to 20 hours. Hotter temperatures speed up the setting time, while cold temperatures slow it down. And if it’s too cold—i.e. below freezing—concrete will not set.
Like curing, you can control the setting of concrete. Ready mix concrete suppliers can add chemicals (admixtures) to speed up or slow down the setting process, depending on the concrete project needs.
So if it’s cold out, accelerating admixtures will speed up the setting time. And retarding admixtures will slow down the setting time in hot weather.
The curing of concrete is an important process that cannot be overlooked during concrete projects. So make sure you use a proper curing method and for the right concrete curing time. Also order a strong enough concrete mix for your specific concrete project to get a durable, long-lasting finished product.