The Most Effective Concrete Curing Methods: Know Before Curing

Concrete is a highly durable and robust building material. Property owners are getting inclined toward incorporating concrete in their construction projects. There are different types of concrete blocks for various purposes of construction. However, a specific set of rules need to be followed to ensure maximum durability and strength of concrete. Curing concrete is one of those critical processes that safeguard concrete’s durability.

What is Concrete Curing

Concrete is made of cement and other additives. Cement requires a hydration reaction to bond with other elements. Hydration is a chemical reaction between cement and water that results in the hardening and setting of cement. Concrete curing is the process of maintaining sufficient moisture in concrete within an acceptable temperature range for enabling cement hydration. The concrete must be kept damp or moist until the hydration of concrete is complete and adequate strength is attained. The curing of concrete should be started right after the initial concrete setting or after removing formwork. The curing process should be maintained according to climate temperature, location, concrete type, and other factors. The hydration of cement can take up to weeks before attaining desirable strength. So, concrete curing is a time-consuming and elaborate process.

Different Types of Concrete Curing Methods

The primary objective of concrete curing is to keep the concrete moist by stopping the loss of moisture and enabling hydration to take place until it gains desirable strength. It can be done in two major ways:

• Preventing moisture loss from the concrete for some period by leaving shuttering/formwork in place, covering the concrete surface with some impermeable membrane after the removal of formwork, or by combining similar methods.
• Constantly wet the concrete surface so that it can remain moist, and no moisture can escape from the concrete. The concrete surface is usually sprayed with water or ponded to enable this method.

There are many different concrete curing methods. Some of the most popular and effective concrete curing methods are:

Water Curing

Water curing is considered the most efficient and easily accessible concrete curing method. Water curing is also most appropriate for specific work types, e.g., curing floors. Water curing involves ponding, sprinkling, and wet coverings.

Ponding and Immersion

Ponding requires a pool of water to stay in place for several days until the hydration process finishes. It can be done on flat surfaces such as pavements and floors. Earth or sand borders are built around the perimeter of the surface in order to retain the ponding of water on the concrete surface. The ponding process is an effective method to prevent the loss of moisture from concrete. Moreover, this method can help maintain a stable temperature which is highly beneficial for efficient concrete curing. However, the ponding method might become impractical for large construction projects.

The concrete precast elements like concrete blocks are typically immersed in water in curing tanks for a particular duration. Immersion helps to facilitate hydration reaction for concrete blocks.

Sprinkling and Fogging

One of the most effective concrete curing methods is to continuously sprinkle water on the concrete surface. If sprinkling of water is done at intervals, adequate measures must be taken so that the concrete surface does not dry out, which can hamper the hydration reaction. The sprinkling system is essential in this method. There are sprinklers and mechanical systems for spraying water evenly on large surface areas. If one of these systems is adopted for concrete curing, it can keep the concrete moist for proper hydration reaction. The continuous water supply prevents any chance of cracking due to repeated drying and wetting of concrete. However, it is a costly system as it requires a lot of water compared to other methods. Moreover, this method demands an adequate water source near the construction site and careful supervision to maintain a perfect balance.

The spraying and fogging method are particularly helpful when the ambient temperatures are well above freezing and the humidity is not that high. Nozzles are used to create a fog mist on the surface of the concrete to raise the relative humidity of the air. Higher humidity prevents evaporation from the surface of the concrete. Fogging is also used to minimize cracking.

Saturated Wet Coverings

Many construction projects have adopted wet covering for concrete curing. Hessians, plastic, or other wet covering that can retain moisture are considerably used for curing. These wet coverings should be applied soon after settling the concrete to minimize any surface deformities. One of the challenges presented by the wet covering method is to cover the edges of slabs such as pavements or stairs. The fabric must cover all surfaces, and the fabric should remain moist enough to retain a coating of water beneath its surface.

Membrane Curing

It is not possible to find a good water source on all construction sites. Sometimes sourcing water from far away locations can spike the construction cost by a lot. Moreover, in some locations, there is an acute shortage of water. Excess water use for concrete curing does not remain an economically viable option.

The amount of water generally mixed for making concrete is more than enough to facilitate the hydration of cement if the water is not allowed to leave the body of concrete. Membrane curing or sheet curing method takes advantage of this point for concrete curing.

The membrane curing method may not be as effective as water curing, but it can bring satisfactory results except for some particular construction works. Membrane curing can be carried out easily on both vertical and horizontal concrete surfaces.

Polythene Sheet

A simple but effective way of capturing moisture in concrete is to use a 125-micron or 500-gauge polythene sheet to cover the concrete surface. ASTM C 171 sheet materials specify 0.01mm of thickness for polythene used for concrete curing according to The Balance. Workers can easily handle polythene sheets, which can be stored without any difficulties. It is usually cheaper than other materials and can be used on different construction works afterward. Before applying the impervious polythene sheet, the concrete surface should be hard enough to prevent surface damage. When polythene sheets are used to cover flat surfaces like floors, pavements, or slabs, they should be extended beyond the slab’s edges by a length of at least twice the thickness of the slab.

The polythene sheet should be placed in the appropriate position as soon as possible. It should be placed within half an hour on vertical surfaces after removing formwork and slabs as soon as the concrete gets hard enough to resist surface damage. The concrete will dry out if the covering sheet is not placed within a suitable time frame. Furthermore, it is of utmost importance that the exposed edges and the corners of the coverings are pinned down. Otherwise, winds can blow away the sheet coverings and can cause damage to the concrete surface. So, a large surface area covering sheets must be joined together to prevent the chances of tearing or ripping. If possible, it is recommended to spray water on the concrete surface before placing the polythene sheet.

Spray-on Compounds

Many curing compounds are available in the market that can be used for concrete curing by spraying on the surface. These compounds can be sprayed using regular garden sprayers on horizontal and vertical surfaces. Using the correct compound ensures a proper curing process. Curing compounds usually consist of a resin in a solvent that evaporates after application. It leaves behind a thin, continuous film of a membrane that traps the moisture in the concrete.

These spray-on curing compounds are available in two different grades. The most common one has a curing efficiency of 75%, and a super grade provides almost 90% efficiency according to Concretenz. These compounds are available with aluminized pigments or with a fugitive dye. The aluminized pigment allows a white layer to be implemented on the surface of exposed concrete, which can reflect most of the sunlight, hence keeping the concrete cooler and moist.

Compounds with dye allow checking that the layer applied is uniform all over. It is essential to apply the compound uniformly to cover and protect all the concrete surfaces. The dye disappears or evaporates on its own, leaving no stain on the concrete surface. However, the dye compound should never be applied on dry concrete as it can increase the probability of leaving behind a stain. The compounds should be applied immediately on vertical surfaces after removing formwork. If the surface dries out due to hot weather, it is advisable to wet it down with clean water and spray the compounds while the concrete surface is moist. Curing compounds are generally non-toxic. However, approval and further testing should be done before using these compounds on concrete to hold drinking water.

Extra safety measures should be adopted while using curing compounds. Workers should be wearing gloves, goggles, and masks to protect themselves. The compound should not get into the eyes, skin, or mouth as it might cause harm. Following safety protocols can increase the cost of using compounds for concrete curing.

Temperature Controlled Curing

Concrete’s strength gain is a function of time and a function of temperature. A high temperature can accelerate the hydration process, which helps the concrete achieve desirable strength in a shorter period without sacrificing anything. However, moisture in the concrete is an essential requisite when heat is applied.

Steam Curing at Ordinary Temperature

It is one of the concrete curing methods used for precast concrete elements. Application of steam to construction projects is a sophisticated task. All concrete products are stored in a steam chamber for the steam curing process. In this chamber, steam is applied either continuously or at intervals. Concrete can reach its strength much earlier than standard curing methods in this process. If done correctly, concrete can reach its desired strength in only three days instead of 28 days.

Steam Curing at High Temperature and Pressure

In this curing method, concrete products are placed in a closed chamber. Superheated steam at high temperature and high pressure is applied to the concrete products that accelerate the hydration process. This is also known as “Autoclaving.”

One of the significant benefits of using this method is it cuts down the curing time by a significant margin. Concrete can gain full strength in a day or less than it usually gains over 28 days of the curing period. Furthermore, the concrete does not lose any strength at a later stage. This concrete curing method is highly effective in building a higher sulfate resistance. It also enables concrete to show lower drying shrinkage and moisture movement.

Infrared Radiation

It is a popular method in colder environments like Russia. It is claimed that infrared curing helps get rapid strength gain compared to the steam curing method.

Electricity

Electrical curing is also the method used in colder climates. It is not an economically viable option in ordinary climate situations. The electrical curing can be done by passing alternating current through electrodes placed on the concrete surface.

Miscellaneous Methods

There are some other non-conventional concrete curing methods. Some construction projects adopt these measures for concrete curing according to their convenience.

• Chlorides are often used as a surface coating or as an admixture. It can be used as an excellent curing medium. Calcium chloride is a salt that shows an affinity for moisture. It absorbs moisture from the atmosphere and retains it at the concrete surface.
• Formwork can also help to retain moisture in the concrete. So, leaving formwork from the surface can help create a moist environment for the concrete.
• Formwork joints can be sealed using wax or other sealing compounds to trap the moisture inside and facilitate hydration reaction in the concrete.

When Should You Start Applying Concrete Curing Methods?

Concrete curing is an essential step that allows it to gain strength. The curing process should not be delayed as it can severely hamper the durability of the material. Concrete curing time depends on many factors, including weather conditions where the concrete is placed, whether placed between forms or directly over flat surfaces, submerged in water or placed vertically, and other specific conditions.

However, it is advisable to start concrete curing as soon as the hydration reaction starts taking place in the concrete. If concrete gets dry quickly, cracks can appear, becoming vulnerable to the exposed environment.

Which Concrete Curing Method is the Best and Why is it Important?

There are numerous concrete curing methods practiced worldwide. Each method caters to different environmental conditions and construction purposes. So, the best concrete curing method depends on your construction type and environmental factors. In Bangladesh, the water curing method is the most popular one. The housing sector relies on this method for concrete curing.

In order to ensure the quality and durability of your concrete structure, a good curing process is an absolute necessity. If curing is done correctly, concrete can achieve its maximum strength and remain rigid and robust for a long time without showing any cracking or aging signs. This process should not be delayed and should be started as soon as it is placed, and the hydration reaction begins. The whole process should be monitored thoroughly. In Bangladesh, water curing is applied in most construction projects. If the water evaporates, the concrete underneath cannot achieve maximum strength and might crack due to drying. Concrete curing can become a challenging task under extreme weather conditions where it can become challenging to maintain a stable amount of water on the concrete surface.

Summary

The curing of concrete is an essential aspect of the construction process. Only an adequately monitored concrete curing can enable it to gain its maximum strength. Among the various concrete curing methods, select the one that suits your needs and budget accordingly. However, make sure skilled workers are tasked to do this job as it requires good experience to know how to maintain a stable condition that allows a suitable environment for the curing of concrete.

Frequently Asked Questions (FAQs)

What is the most common method of concrete curing?

Ans: Water curing is the most common method of concrete curing.

What is the minimum curing period of concrete?

Ans: To gain maximum concrete strength, the minimum curing period is 28 days.

What will happen if I don’t cure concrete for 28 days?

Ans: It takes a minimum of 28 days for the hydration process to finish in concrete. If the concrete is not cured correctly, cracks might appear, and it will not gain sufficient strength.

What is the fastest way of curing concrete?

Ans: Steam curing at high temperature and pressure is the fastest way to cure concrete. Furthermore, the curing process can be accelerated in the water curing method by applying slightly warmer water instead of using water at normal temperature.

What happens if the concrete dries too fast in hot weather?

Ans: If the upper surface dries out due to hot weather, it will shrink while the bottom part remains the same. This can cause instability in the concrete structure resulting in a weak structure and reduced compressive strength.