What's In This Article
Concrete is one of the most remarkable building materials ever created. With a history dating back thousands of years, concrete’s incomparable versatility and legendary strength have enabled its use in construction projects ranging from buildings to bridges to streets.
To deliver peak performance, concrete must contain the right mixture of cement, aggregate material, and water. As importantly, concrete must dry and cure properly to harden into its final form.
Keep reading to find out how long it takes for concrete to dry and learn the crucial difference between drying and curing.
Concrete is a highly versatile and incredibly durable building material used in all types of construction projects, from small jobs to major builds. Although it has been in use for many centuries, concrete is one of the most heavily relied-upon resources in the modern world, and there are no signs that this will be changing anytime soon.
So what exactly is concrete?
What Are the Components of Concrete?
Concrete is a mixture of several components and undergoes several stages of preparation and application before reaching its final, hardened form. Generally speaking, concrete is a blend of:
- Portland cement – this is the key component of concrete and is typically made from a combination of materials, including chalk, clay, iron ore, limestone, shale, silica sand, and slate, which are mixed, heated, and then ground into a fine particles
- Aggregates – these materials (typically sand, crushed rocks, and rough gravel) bind with the paste created by mixing portland cement with water and give the concrete its durability and rock-like strength
- Water – when mixed with portland cement, water creates a pasty substance that binds to the aggregate materials in concrete through a process called hydration, creating a thick slurry that eventually hardens into concrete’s final, familiar form.
What Is Hydration?
The key to concrete’s incredible strength and longevity is a chemical process known as hydration. When Portland cement and water are combined, the resulting mixture forms a thick paste.
As this paste is mixed with aggregates like sand and gravel, nodes on each cement particle attach to adjacent cement particles and form a coating on aggregate materials in the concrete mixture.
These bonds strengthen and harden as the concrete cures and dries. Contrary to popular belief, drying and curing are not the same thing; on the contrary, they are different processes that play equally vital roles.
What Is Concrete Used For?
One of concrete’s most appealing qualities is that this versatile building material is putty-like and easily workable when poured. As it dries and cures (more on these concepts later), concrete hardens and eventually becomes incredibly durable and strong.
Throughout the centuries, humankind has found new ways to use concrete, and even though it has been around for so long, it continues to be the world’s go-to resource for building projects ranging from small to massive.
Here is a sampling of the types of jobs concrete can be used for:
- Skyscrapers and other large buildings
- Bridges and infrastructure
- Sidewalks and walkways
- Streets, highways, and railways
- Airports and major facilities
With the increasing urbanization of underdeveloped areas, the use of concrete to construct vital infrastructure and modern buildings only figures to grow.
Factors Affecting Drying Time
Concrete is such a versatile building material that it can be used in countless ways for jobs, small and large. But because there are so many applications for concrete, drying times can vary from one project to another. There are certain factors to consider when determining how long concrete will take to dry, including:
- Moisture content – water is a key ingredient in concrete, and it stands to reason that the greater the moisture content, the longer the drying time
- Temperature – drying time is also affected by the temperature that the setting concrete is subjected to, with lower temperatures leading to longer drying times and warmer temperatures corresponding to shorter trying times
- Humidity – concrete will dry faster in dry, arid weather compared to moist, humid conditions
- Air circulation – just as lips become chapped on a windy day, moving air can carry away more moisture as it circulates above setting concrete.
- Mixture type – certain types of concrete, such as so-called quick-dry formulas, dry faster than other types
For concrete to achieve optimal strength and durability, it must be allowed to dry completely. Knowing how certain variables can affect concrete as it sets will enable you to plan your project to allow for uninterrupted drying times.
Types of Concrete
One of the reasons that concrete is such a popular building material is its versatility. Concrete comes in different forms, and each is suited for particular types of applications.
- Ready-mix concrete is the most common type of concrete and represents 75% of all concrete used
- Precast concrete is used to prefabricate building materials like bricks, panels, and pillars.
- Pseudo-concrete materials like mortar and trout are similar to concrete in that they are cement-based
- New concrete materials are being developed with modern aggregates to form items like roofing shingles, tiles, and countertops.
Different types of concrete dry at different rates, with those relying on less water in the mixture or containing special binding agents typically drying faster.
Drying Time of Concrete
Concrete can harden to a rock-like mass suitable for any construction project with proper application. For it to reach this final state, however, concrete must be allowed to dry completely, and there is more to this process than meets the eye.
Depending on the thickness and the type of mixture, concrete can be dry to the touch in as little as one hour after pouring. But just because concrete feels dry does not mean it is ready for its intended use. Here are a few facts to consider regarding the drying time of concrete:
- Generally speaking, within 24 to 48 hours after pouring, concrete can hold its shape and is dry enough for the supporting framework and forms to be removed
- At this time, concrete is hard and set enough to support light foot traffic
- After seven days, a 4-inch thick slab of concrete has dried to the point of achieving 70% of its anticipated strength
Because concrete has so many uses and applications, drying times will vary between jobs, but a good rule of thumb is that every inch of concrete thickness will require 30 days to dry completely. Thus, if you pour concrete to a depth of four inches for a new driveway, you can expect it will take approximately 120 days to dry completely.
An important concept to grasp when learning about concrete and its unique attributes is that drying and curing are not the same thing. Where drying involves the release of moisture from concrete, curing involves the opposite.
For concrete to properly harden, it must retain moisture to allow powerful chemical bonds to form between the portland cement and the aggregate materials. These bonds take time to strengthen, and this process, known as curing, cannot be rushed or cut short, or else the structural integrity of the concrete may be compromised.
Just like drying times, job conditions can affect the amount of time it takes for concrete to cure, but these are the typical curing times for most projects:
- After 24 to 48 hours from pouring, the concrete has cured enough for it to support the weight of people walking on it
- After seven days, the curing process has advanced far enough for light vehicles to be driven on concrete
- After 28 days, the process is complete, and the concrete is fully cured
Effects of Premature Drying
Proper drying is crucial to the overall strength and durability of concrete. If the drying process is cut short or sped up too much, the quality of the concrete can be compromised. Effects of premature drying can include:
- The formation of cracks on the surface
- Shrinkage of the concrete from its intended shape and size
- Reduced strength, hardness, and durability
Together, these effects diminish the aesthetic qualities of concrete and, more importantly, compromise its structural integrity, leading to catastrophic failure.
Tips for Drying and Curing Concrete
Drying and curing are crucial steps when using concrete as a building material, as it is during these phases that concrete develops its strength and durability. Here are a few tips for drying and curing concrete:
- Control moisture levels in concrete by spraying water on the surface or laying wet materials on top of it
- Plastic sheeting or waterproof paper laid on top of concrete can provide a protective barrier that traps moisture and allow proper curing.
- Blankets and heating pads can protect concrete from harsh conditions like freezing temperatures.
- Keep forms and molds in place until allotted curing and drying times have elapsed
Taking measures such as these ensures that the concrete you have poured will cure and dry as needed to achieve optimal strength and longevity.
Concrete is one of the world’s most widely used building materials and for a good reason. It is easy to use, has numerous applications, and is incredibly strong and durable. But to produce these characteristics, concrete must be properly prepared, applied, and most importantly, it must be allowed to cure and dry fully.