Curing is an important process for concrete because it increases strength, durability, volume stability, and resistance to freezing and thawing. It also helps prevent abrasion and scaling and ensures water tightness.
Curing is influenced by several factors including outside conditions, water content, and mix type. The minimum curing time is 24 hours for foot traffic and 10 days for vehicles, but it usually takes up to 28 days to achieve full strength.
Temperature
During the curing process of concrete, the temperature plays an important role in the strength and durability of the material. It can affect the hydration process by affecting the chemical reaction and thus increasing the time to set and final strength.
In order to maximize the strength gains of concrete, it is imperative that the hydration process is controlled by monitoring temperatures throughout the entire curing process. This can be achieved by installing thermocouple data loggers before the pour to keep track of the temperature of the concrete over the course of a project.
Thermocouples can also be placed inside of the concrete to ensure that the mix stays at an acceptable temperature until it is ready for placement. Keeping the concrete at an ideal temperature allows it to hydrate quicker and achieve full strength in less time.
It is also important to note that when concrete is exposed to freezing temperatures, it may not be able to cure properly. This is because cold temperatures can stop the hydration process altogether and cause the concrete to lose its strength.
To prevent this, it is essential to keep the concrete warm during the early stages of curing. Using large industrial warming blankets, concrete contractors can keep the concrete at an ideal temperature for 24-48 hours until it is ready to be placed on the ground and begin to take form.
A hydration test conducted on samples of concrete cured at different curing temperatures demonstrated that the water absorption rate increased significantly at elevated curing temperatures (30 degC and 40 degC), however, this increase was relatively small. The results of the tests showed that, after 3 and 7 days of curing, the early strength (MPa) of concrete cured at higher temperatures was significantly lower than that of concrete cured at the lowest temperatures (12 degC).
Another way to help speed up the hydration process is to add calcium chloride to the mix. This can increase the water-cement ratio and accelerate hydration, though it can also be toxic to the metals that are used in construction. To avoid this, it is recommended to use non-chloride alternatives for hydration.
Water
Concrete is a popular material that can be used for many purposes. It is very low-cost and reliable, which makes it an excellent choice for construction projects around the home. However, it is important to understand how concrete works before using it for a project.
Water is one of the key elements of concrete curing. It is essential to the strength and durability of the final slab, as it is required for the hydration process that enables concrete to form its tough and resistant surface.
It can be injected or sprayed directly on the concrete, as well as pumped through pipes and hoses. The amount of water used should be adequate to ensure that the proper proportions are achieved for the type of concrete mix used, while also ensuring that the concrete has sufficient moisture.
This helps the cement to hydrate, which results in a sticky gel that sticks to the aggregates without washing away. Once this is achieved, the concrete sets and becomes solid. It doesn’t become cured until the concrete has been in place for enough time to allow it to reach its final setting phase, typically 28 days.
How quickly the concrete dries depends on its temperature, how much water is used, and how strong it is. If it dries too quickly, it will not be as strong and will likely collapse.
Curing is essential to the strength of new concrete, so it must be done before placing heavy objects on the slab. This is to protect it from cracking and collapsing.
There are several different methods of curing, but the most common is to flood the surface with water. This is a fast and time-effective method that works by re-wetting the concrete.
Fogging or misting is another way to cure concrete, which involves spraying a fine mist of water on the surface to maintain moisture levels. It is especially useful in situations where the air temperature is higher than freezing but humidity is low.
Ponding is another water-based method of curing, which requires the use of sand or earth dikes to surround the concrete. The slab is then surrounded by a layer of water that is kept continuously damp throughout the curing process.
Compounds
The curing of concrete is an important step in the strength development process. It delays the occurrence of shrinkage cracks until the concrete is strong enough to resist them. It also improves abrasion resistance and reduces water tightness problems.
Curing is the process of controlling the moisture and temperature conditions at both the surface and within the concrete for a period of time, after the concrete is placed. Properly cured concrete has sufficient moisture to promote hydration and develop strength, volume stability, and durability. It also maintains a uniform temperature within the concrete, which is essential for concrete structures that require long spans.
One of the most common ways to cure concrete is by sprinkling it with water (known as “moist curing”). Moist-cured concrete is much stronger than concrete that was not sprayed.
Another method is to use a cover that can trap and slow the evaporation of the mix’s moisture. This can be done by using either a concrete curing insulating blanket or polyethylene sheeting that’s at least 4mm thick.
A third option is to use a membrane-forming curing compound. These compounds retard or reduce the evaporation of water from the concrete, forming a film that seals it and keeps it from drying out. The most commonly used membrane-forming compounds are wax and paraffin emulsions. They are white pigmented and can be sprayed on to fresh concrete.
This type of membrane-forming curing compound also protects the concrete from sun rays and ice crystals. It is a good choice for cold climates or when the concrete is in direct contact with water, such as in swimming pools.
The microstructure of mortars treated with a variety of curing compounds and the reference mortar were analysed by SEM techniques. There was a significant difference in the microstructure between the cured and uncured samples.
During the process of curing, the cement and water are bound together by chemical reactions to form calcium hydroxide crystals that strengthen the concrete. Over the curing period, these crystals grow and harden until the concrete is able to withstand pressure.
Coverage
Curing concrete is an important process that improves the durability, strength and water tightness of the finished product. However, it takes a long time to complete the process and there are some factors that can affect the curing time.
Temperature is a major factor in curing concrete, since it directly affects the hydration process that leads to strength development. Cold concrete slows down the hydration reaction, while hot concrete accelerates it.
In general, the ideal temperature for curing concrete is between 60 – 80 degrees F. This is a good range because it allows the concrete to maintain ideal thermal temperatures, which helps to ensure strength development occurs correctly.
Another factor that can make a big difference is the coverage of the concrete. Covering can help to retain the moisture in the concrete and delay evaporation.
This can also prevent the concrete from drying too quickly which could cause cracking and other problems. For this reason, it is recommended that the cover be applied after concrete has been poured and fully wet.
A curing cover is typically a sheet that is covered with a layer of fabric to help retain the moisture and delay evaporation. It can be used on the ground, scaffolding or for flooring and works by reflecting incoming solar radiation from the sun.
The thickness of the concrete cover can also impact the curing time. Usually, the cover is designed to be about a quarter inch thick, but it can be a little more or less depending on the weather conditions.
When the cover is placed on the slab, the bleed water rises as the mixture settles, and then the cover needs to be removed after about a day for the evaporation rate to be monitored. If the bleed water is evaporating too quickly to keep the surface wet during this period, you will need to do some initial curing (usually about a week).
The final set of a concrete slab is when the surface of the concrete is completely cured and no more bleed water is rising. If you are going to paint or stain the concrete, it is important that you wait until the surface of the concrete has cured for at least 28 days to avoid plastic shrinkage cracks.