Posted on July 02, 2019
The process of curing concrete is an important step in providing sufficient hydration to the building material. This is achieved by employing specific methods to maintain a certain level of moisture, and prevent the fall of temperature brought about by heat loss.
Curing concrete also allows it to reach its optimal strength. The longer that it is left to cure, the more durable it will be.
Some of the popular techniques for curing concrete are as follows:
Techniques To Maintain Moisture In Concrete
These methods typically involve keeping the surface area of concrete exceptionally wet. This can be achieved by:
Ponding
This technique is ideal for curing concrete on flat surfaces such as floors or pavements. It is very labor intensive, and therefore best-suited for small scale projects.
Ponding is a method of thermal curing where sand dykes are set up around the perimeter of the surface area, and water is pooled within the perimeter to retain moisture over the surface. This effectively regulates its temperature, but may be challenging to carry out during chilly weather conditions.
Water of not more than 11°C (20°F) may be used for this method as it prevents cracking. Also, contaminant-free water is more appropriate to ensure pristine appearance of the concrete.
Fogging
The method of fogging works best for flat surfaces, and entails frequent spraying onto the surface of the concrete through water jets. This technique is better suited for construction sites where humidity is low, temperatures are near freezing, or where chances of evaporation are high.
This method also provides insulation against temperature changes, and slows down the process of evaporation. It proves effective when used to reduce plastic shrinkage cracking; however, the cost of maintaining a steady supply of water may make it costly.
The concrete needs to retain a certain level of moisture between spraying intervals to avoid cracks from forming. However, the concrete needs to be set efficiently before spraying, or it could lead to water erosion in the building material.
Saturated Wet Coverings
Wet moisture soaked burlaps placed on concrete surfaces also aid in the prevention of moisture evaporation, and act as surface protectants. This technique is most effective when used alongside polyethylene covers.
The preferred fabric must be kept constantly wet during the curing process. The use of wet sand, sawdust, or hay is ideal for small jobs; however, these can result in discoloration or deterioration if the quality of materials used is not good.
Techniques To Reduce Water Loss
These techniques prevent moisture from evaporating into the atmosphere. This can be achieved by:
Paper Or Plastic Sheets
The use of polythene sheets or paper sheets is an easy way to restrict the contraction of air, and the concrete surface; leading to a reduced amount of evaporation.
This method also prevents excessive loss of moisture and controls the rate of evaporation, proving ideal for both vertical and horizontal surfaces. Additionally, it prevents dust particles from sticking to the concrete due to the added layer of protection.
It is important to note that impermeable waterproof building paper provides better results than ordinary vapor-permeable sheets when attempting to control evaporation. Paper covers include asphalt or bitumen coverings, while paper backed plastic and copper sheets are excellent for curing.
However, this technique does not replenish any loss of moisture within the concrete. Also, strict supervision is required when undertaking this process, as strong winds can blow the sheets away.
Applying Membrane Compounds
This is the most popular and easy method to apply as it can be sprayed, and needs minimal supervision.
A layer of impermeable compound coats the concrete surface, thereby sealing in the water while effectively avoiding evaporation. These can maintain up to 80% of the humidity in a batch of concrete for a week.
It is available in three different bases; synthetic bases, wax bases, and a combination of the two. It is advisable to layer two coats to further prevent any pinholes from leaking moisture into the air. The standard grades offered are available with either 75% or 90% curing efficiency.
The aluminized variety is appropriate for outdoor use as it deflects the sun rays, while the fugitive dye must be avoided on dry surfaces.
Techniques To Supply heat
Concrete is exposed to forms of heat to accelerate the hydration process. This is achieved through:
Applying Live Steam
Concrete is exposed to steam at a low pressure of up to, or less than, 140 degrees Fahrenheit. This accelerates the hardening process, and retains the concrete’s moisture which results in an effective curing process.
However, it is important to note that this process is more effective for colder climates.
Concrete cured by this method can attain optimal strength in 3 days, which is normally achieved in 28 days through other methods.
This technique is also ideal for enclosed structures or large precast units, and requires special materials and labor; additionally, the initial cost of this process is comparatively higher.
The Use Of Heating Coils
This method is used to prevent concrete from freezing in extremely cold weather, and calls for the placement of heating coils near the surface of concrete.
Heating coils regulate the concrete’s internal temperature, and circulate warm air around the surface which reduces shrinkage by up to 30%. However, this method requires careful control and supervision thought out the process.
There are numerous methods that can be used to cure concrete; and the exact technique to be used is usually dependent upon the quality of materials used and the method of construction employed.
Also, when choosing the most appropriate method for curing of your concrete, it is important to take into consideration the intended use of the concrete.