This article will guide you on the frequent queries on concrete’s drying and hardening process and how to hasten it. You will also be informed of the different terminologies such as curing, drying, and setting.
What is concrete?
Fine and coarse aggregates are mixed with liquid cement to form concrete, which hardens to a solid-state over time. When combined with aggregates and water, cement serves as a binding agent.
Poured and smoothed, it hardens into the sturdy substance utilized in many building projects. Water, Portland cement, and aggregate (sand, rock, or gravel) are the three main components of most concrete surfaces. Therefore, the production of concrete must be completed on schedule. Once it’s ready, it must be put to use immediately; otherwise, it will harden.
The difference between concrete and cement.
A common misconception is that cement and concrete are interchangeable terms. The difference is that cement is primarily used in the production of concrete. To create it, water and cement are used in the manufacturing process to create it—concrete tanks house the raw materials, which are spun and combined at high speeds to produce this. Then finally, concrete is made from the resulting paste.
How to fasten the concrete’s hardening process
Concrete never completely hardens; it just gets a little harder. This is because the cement particles react with the water in the mix to determine how concrete hardens. Concrete hardens as it forms connections with water molecules.
Even after reaching what is often referred to as “full strength,” your concrete will continue to harden somewhat due to microscopic moisture bubbles. Warm water can be added to the mix to speed up the setting and drying process. When lukewarm water is added, the reaction accelerates dramatically, resulting in the creation of bonds.
What is concrete curing?
The most common misconception about curing involves nothing more than keeping the concrete’s surface damp. However, that is only one aspect of curing; it’s also about providing the concrete with everything it needs to become strong. A concrete’s strength is determined by the development of crystals inside the concrete matrix.
Curing prevents drying shrinkage until the concrete is strong enough to withstand shrinkage cracking. Properly curing concrete increases strength, durability, water tightness, and wear resistance.
Factors that lead to concrete cracking
Here are some factors that contribute to concrete cracking.
Hydration
A chemical event known as hydration is responsible for forming these crystals. Insufficient water prevents the crystals from forming and the concrete from gaining strength. However, with enough water, the crystals form tiny rock-hard fingers that encircle and intertwine with the sand and gravel in the mix.
Temperature
Temperature is another critical factor in curing; the concrete can’t be too hot or too cold. The hydration reaction slows down when new concrete cools. Consider the concrete temperature, not the air temperature. Hydration decreases significantly below 50 degrees Fahrenheit; below 40 degrees Fahrenheit, it ceases altogether.
Exothermic reactions
Exothermic reactions (which create heat) can induce temperature differentials inside the concrete, leading to cracking in hot concrete, the polar opposite of the abovementioned problem. In addition, when cement reacts rapidly, the crystals don’t have time to build correctly. Thus it doesn’t have the strength it should.
What are: curing, drying, and setting?
Like any other industry, the construction sector has a wide range of terminology that has a specific meaning to those working there. Cement, sand, and other materials go into the creation of concrete. Once the concrete has been poured, the curing, drying, and setting occur within the material.
Curing
It is the hydration process that impacts the cement-aggregate bond. Curing is the process of keeping the liquid at a temperature above 50°F for three to fourteen days after pouring it. There will be no end to the curing process if moisture is present.
The fact that concrete would continue to respond even after 28 days is a testament to its impermanence. After the concrete has been poured, the hydration process strengthens the final product as time passes.
Drying
Drying is known to provide the appropriate conditions for concrete to cure the moisture level required for its intended usage or installation of floor finishes. It may take up to 48 hours for freshly poured concrete to become dry enough to walk or drive on and 28 days for the concrete to be completely dry.
For the concrete to be declared dry, it must have a moisture vapor emission rate (MVER) of 3lb/1000sqft/24-hours or less, including wood, vinyl, and linoleum floors, as well as epoxy coatings.
Setting
Once the concrete has been laid, it begins the process of setting, which is the slow transition from a liquid to a solid. This is due to the Calcium silicate hydrate and ettringite production and can be impacted by the water content in the mix. After setting, the concrete is still soft and requires time to cure and dry thoroughly before it can be considered fully hardened.
Within 30 minutes of placement, concrete begins to set and is deemed complete after 10 hours. A Penetrometer measurement of 3.43MPa or 500 psi generally indicates the beginning of hardening, while a reading of 26.97MPa usually indicates the conclusion of hardening.
Factors that affect concrete drying time:
It is not always possible to predict concrete drying timeframes. The time it takes for concrete to dry depends on various factors. There are a few of these:
Moisture
In the absence of water, the concrete will cure faster. The cement’s contact with water causes the curing process. Your concrete may not be as strong as you need or anticipate because there is less bonding. It will take longer to cure if there is too much water in the concrete, and you may notice flaking on the surface.
Temperature
Moisture evaporates more quickly when the temperature increases, which means that your concrete will harden more quickly. To speed up the curing process, you can use a concrete blanket to keep it warm. This can be very helpful in cold weather while trying to cure concrete.
Mix design
You may speed up the curing process of your concrete by adding an accelerant to the mix. However, full-strength concrete made this way may not be as sturdy as concrete that has been allowed to cure to full strength regularly.
How to hasten the drying process of concrete
There are ways to speed up the hardening process of concrete so that it may be utilized sooner, such as using additives. Pre-mixed and post-mixed concrete can both benefit from a wide range of additives.
The pace of drying can also be affected by the type of concrete utilized. However, regardless of the manner or kind of concrete utilized, concrete will take 28 days to reach 99 percent of its strength.
Before pouring
The early setting and drying durations of concrete can be accelerated several ways before it is poured. For example, the first drying period can be shortened by using less water or increasing the cement percentage. Pouring on a sunny, warm day can expedite the process even further.
Add calcium chloride before pouring.
When combining concrete, use warm water instead of cold water—preventing ground moisture absorption into the concrete by laying down a moisture barrier before pouring allows the concrete to dry more quickly.
After pouring
There are various techniques to expedite the drying process of concrete once it has been fully set up. For example, moist curing takes the longest, while pond cures can be completed in half the time of dry or regular curing. Here are steps to hasten the drying [rocess.
Use a dehumidifier
It is possible to utilize dehumidifiers to eliminate moisture from the air, which allows the concrete to dry more rapidly. For example, if you use a dehumidifier inside and close the windows and doors, the relative humidity inside will also fall, and no moisture will be drawn in from the outside.
Use a heater
Concrete sets and dries faster in warm conditions than in the cold, thus utilizing heaters to raise the temperature.
Cover the pour with a black plastic sheet
With a black plastic sheet over the pour, you can keep moisture from escaping and speed up the curing process. The end product will be more robust because of this. The use of troweling methods can also aid drying.
However, as a precaution, it is essential to remember that excessive or hard-troweling of cement might shut and so slow down the drying process.
Moist curing and pond curing
It is possible to keep the concrete surface damp for up to seven days by watering it five to ten times a day for up to seven days. This method employs berms or other containment to trap a few inches of water above the concrete to aid in curing. It speeds up the drying process because it achieves the same as moist-curing in three days instead of seven.
Frequently asked questions
What process does a concrete undergo to dry?
During the drying process, water evaporates from the surface of the paint. Capillaries bring moisture from the concrete mass to the surface to replenish the water that has evaporated and then evaporate themselves.
As long as the moisture in the air is more than that in the concrete, evaporation will occur. The moisture in the concrete might therefore continue to evaporate even after it has been declared dry.
How much time is needed for concrete to completely dry?
Concrete becomes more and more brittle and dry with each passing day. However, the 24-48-hour hardening process is sufficient to make it ready for walking without leaving any marks. After seven days, driving is allowed since about 70% of it is cured. Meanwhile, heavy rolling vehicles and other equipment are acceptable after 28 days.
Why does concrete harden?
Concrete combines Portland cement, aggregates like sand and gravel, and water that is poured into a mold to form a solid. In addition to the silicates, Portland cement includes tricalcium aluminate, tetra calcium aluminoferrite, and gypsum, all of which contribute to concrete’s strength and hardness.
When water is added to cement, hydration occurs, resulting in chemical reactions that establish links between the cement and the aggregate. For the initial bond strength, tricalcium silicate responds faster, whereas dicalcium silicate reacts more slowly after seven days. When water, dicalcium, and tricalcium silicate combine, a crystalline matrix of fibers is formed, hardening and binding the aggregate mix.
How long does concrete harden indoors?
The crystalline linkages that harden concrete must develop indoors or out on a wet concrete floor. A building’s humidity and temperature may affect how quickly or slowly the concrete binds and how much lighter the color becomes as it solidifies.
Indoor humidity and temperature may be more easily controlled, allowing the hardening process to proceed more quickly and more weight to be supported. However, the hydrating chemical reaction isn’t complete until 28 days.
Conclusion
Several factors affect concrete’s drying time and hardening process. If you want to lessen the drying time, apply any of the steps mentioned above. Also, consider the temperature and humidity as well.
