Despite the crucial role it plays in concrete building, curing is often left to the worker’s preference and comfort. Engineers and foremen on the work site should make extra efforts to make sure curing isn’t forgotten. In this article, we’ll go into the specifics, including why it’s so crucial that cement cures properly.
Curing of concrete: Meaning
Curing of concrete involves keeping it wet enough to facilitate cement hydration at the initial stages and warm enough to prevent the concrete from drying out too quickly. Hydration is the process in which water and cement undergo a chemical interaction that leads to the development of a variety of compounds that contribute to the cement’s setting and stiffening.
Preliminary concrete temperature, atmospheric temperature, concrete size, and concrete mix architecture all have an impact on the hydration process. Because of this, on-site concrete has to be kept at a temperature and moisture level that encourages this chemical reaction to occur rapidly and continuously.
Curing of concrete: Why is it necessary?
Curing of concrete is necessary for a variety of reasons, including the following:
- In order to stop the concrete from becoming too dry very quickly from the effects of the sun and the wind. This avoids the plastic shrinkage that might occur in concrete.
- By permitting the process of hydration to take place, it contributes to keeping the temperature of the concrete stable. In order to proceed, the hydration process must have access to water and generate heat.
- Curing causes the concrete to become more rigid and strengthens its bonds with the components and reinforcements included inside it. This serves to avoid damage to the link between the cement and the reinforcement that might otherwise be caused by vibrations and impacts.
- This contributes to the construction of concrete that is long-lasting, impervious, and crack-free.
Curing of concrete: What is the optimal time?
The pace at which the moisture in the concrete is lost to the atmosphere determines when the curing process of the concrete should begin. The rate of evaporation may be affected by the wind, the radiant energy from the sun, the temperature of the concrete, the climate conditions, and the relative humidity.
The disparity in vapour pressure between the air around the concrete and the surface of the concrete itself is what drives the evaporation of moisture. When there is a large differential, there is also a large rate of evaporation. The factors that determine the optimal cure time for concrete are:
-
Initial Curing
After the concrete has been poured and consolidated, water may leak through the surface because of the concrete’s natural tendency to sink. Different elements, such as the concrete’s mix qualities, the depths or thickness of the concrete, the manner of compressing, etc., affect how long and how quickly the concrete bleeds.
The surface moisture of these bleeding objects begins to evaporate. In order to avoid plastic shrinkage fractures in the concrete and limit moisture loss, the concrete must be allowed to cure for at least a week before any finishing work is done, after which the bleeding water will vanish from the surface, and the drying process will begin.
In the beginning stages of the curing process for concrete, several methods such as fogging, the use of evaporation reducers, and the provision of shading devices and windscreens are all viable options.
-
Intermediate Curing
When the surface of the concrete has been finished, but before it has been fully set, an intermediate curing period is performed. This occurs when the concrete members’ desired surface texture is reached quickly or when the setting is slowed.
-
Final Curing
Following the final setting of the concrete, the ultimate curing of concrete should be carried out. Due to the fact that this results in a rapid moisture loss from the concrete surface, this helps to minimise the surface of the concrete from drying out.
Curing of concrete: How long does it take?
When concrete is allowed to cure for extended periods of time, the resulting structures are more robust and long-lasting. Compressive strength, or how well concrete can hold its shape under pressure, improves with age, as seen in the accompanying diagram. The amount of time needed for concrete to cure is dependent on:
- The dimensions of a structural component made of concrete.
- The kind of concrete, the grade of concrete, and the pace at which it hardens.
- The temperature and level of humidity of the surrounding environment.
- Conditions of exposure existed on the surface of the concrete both during and after the curing process.
- The requirement for the amount of time that concrete must cure in accordance with its specification.
The American Concrete Institute (ACI) Committee 301 suggests a minimum curing duration that corresponds to the concrete achieving 70 per cent of the stipulated mechanical properties after the completion of the curing process. Typically, a seven-day curing time is provided, and this time corresponds to roughly 70 per cent of the required compressive strengths.
The Indian Standard IS 456 – 2000 suggests at least seven days of curing time for concrete when using regular Portland Cement, and at least 10 days when using mineral admixtures or mixed cement. In addition, it is suggested that ten days of curing time is the minimum for structures exposed to dry seasons and that fourteen days of curing time is a minimum for concrete containing admixtures or conventional concrete in dry seasons.
Curing of concrete: Methods
Curing processes are implemented on-site and vary according to site restrictions, building type, and other material considerations. Here are some broad classifications of concrete curing techniques:
-
Water curing
Source: Pinterest
The continuous wetting of the concrete’s surface that occurs throughout the water-curing process stops water from evaporating from the concrete’s surface. It is accomplished by applying water or curing ingredients to the surface of the concrete in the form of a mist, a sprinkle, or a spray in order to maintain a constant level of moisture on the concrete. It is possible to prevent moisture from the concrete’s body from evaporating, which in turn adds to the concrete’s increased strength. The following are types of water curing:
- Ponding
- Fogging, sprinkling & mist curing
- Wet coverings
-
Membrane Curing
Source: Pinterest
By encasing the concrete in an impermeable membrane, membrane curing reduces the amount of moisture that evaporates from the surface of the concrete. Wax, acrylics, and liquids based on water may all be used as curing materials. In order to produce an impermeable barrier, they are sprayed over freshly poured concrete. This helps to limit the amount of moisture that is lost from the concrete. The following are procedures for membrane curing:
- Plastic sheeting
- Formwork
-
Steam Curing
Source: Pinterest
When applied to concrete, steam curing maintains surface moisture and increases the temperature to hasten the pace at which strength is achieved. Precast concrete companies, which make items in bulk quantities and need an expansion and improvement or striking period of the formwork, often use this technique.
Curing of concrete: Considerations to make
During the process of curing concrete, there are a few things that need to be taken into consideration.
- It is important to avoid exposing freshly mixed concrete to elements such as the sun, rain, or dry breezes.
- If the climate is going to be hot and dry for the duration that the concrete is curing, a tarpaulin needs to be placed over it.
- After the concrete is poured, the area should be saturated with water for a period of twenty-four hours. The pillars should be wrapped with gunny sacks so that the cure may take effect.
- After the concrete has been poured, the curing process should be let go on for at least fifteen days.
- The quality of the water being used in curing the concrete should be comparable to that of the water used in the mixing process.
- Curing water should be pure and devoid of contaminants like hydrocarbons, chemicals, alkaline solutions, vegetable matter, and so on. When it comes to making and curing concrete and other construction, drinking water is often regarded as adequate.
- There should be no dissolved chlorides or sulphates in the water. The water’s salinity has to be measured. The most reliable technique is a taste test. The ideal range for the water’s pH is between 6.5 and 8.5, making it very close to neutral.
- The use of salt water at any stage of the building process, including curing or any other stage, is not recommended. Two potential problems are salt crystallisation and fast reinforcement corrosion. Both of these might occur.
FAQs
How long does concrete need to cure?
Concrete must normally sit undisturbed for between 24 and 48 hours before it is dry enough to be traversed by foot or vehicle. However, the drying process for concrete is a fluid and ongoing process, and it typically takes around 28 days for the concrete to attain its maximum effective strength.
To what end is curing done?
The curing process is very vital for the development of the concrete's strength as well as its longevity. The curing process begins as soon as the concrete has been placed and the finishing touches have been applied, and it requires the correct temperature and moisture settings to be maintained, both at deep and on the surface, for lengthy periods of time.
How quickly can concrete be cured, if at all?
Water, one of the most crucial elements of concrete, is necessary for the curing process to occur. The curing process might be accelerated by slightly warming the water used in the mixture because doing so will speed up the reaction. However, you shouldn't use water that is too hot because doing so could result in permanent damage.
How is concrete cured?
Curing often involves the application of wet covers that are saturated with water. Examples of such coverings include burlap, cotton rugs, carpets, and other textiles that hold moisture.
What occurs when curing is not performed?
The longevity, toughness, and abrasion resistance of concrete are all negatively impacted when the curing process is not carried out correctly. Insufficient curing causes concrete to develop plastic shrinkage fractures, thermal cracks, and a major reduction in the durability of the upper layers. In addition, the surface layer suffers significant degradation.