GUIDE ON THE CORRECT PROCESS OF CURING CONCRETE

Concrete curing is an extremely important step to have a perfect house or construction. Because in addition to reinforcement, the quality of concrete is one of the key factors to decide the "sustainability" of the house. If there are errors in the construction process, then when there are problems, it is often very laborious to repair, but the results are not necessarily satisfactory. Every step, every step in the process of building a house needs to be done right from the beginning is the best thing.

So why is it necessary to properly maintain concrete and how to properly maintain it, let's find out with we through this article!

Concrete curing is a very important step

What is concrete curing?

Concrete curing is simply the process of keeping the concrete moist after pouring, up to a certain strength under the influence of local weather conditions and human intervention.

The importance of concrete curing 

Engineers or those who have worked in the construction industry for a long time understand that concrete maintenance plays an extremely important role. Many times, concrete is mixed with selected and good quality materials (sand, stone, cement, water) but without proper curing, it will not achieve good quality after pouring. .

Concrete can only achieve the best quality when it is cured in a sufficiently humid environment and without strong physical impact. Therefore, the moisture retention of the concrete needs to be prolonged enough. 

If observed with the naked eye, when the concrete shrinks, it looks frozen on the outside, but inside, the hydration process is still going on. When the environment is too dry, the water in the concrete evaporates quickly and is no longer enough for the hydration process, which will cause the concrete strength to stop developing and cause cracking.

Besides water, temperature is also an important factor in curing concrete. Compared with normal temperature, the hydration rate of cement increases significantly when the temperature rises above 40 degrees. Therefore, in some cases, it is possible to cure concrete with hot water with a temperature of 80-90 degrees Celsius. When the concrete hardens at a rapid rate, the cement hydrates so quickly that it can It can take only 20 hours to reach the intensity of 28 days.

However, if curing concrete by using hot water, it is necessary to be very careful, ensure technique and continuously monitor to avoid danger during construction.

Consequences if not properly curing concrete

Many contractors are negligent or do not understand the technique, but skipping the concrete curing step will have very serious consequences, especially when pouring concrete takes place in the summer, when it is hot.

When the concrete curing process cannot take place because of lack of water, it will lead to cracks, pitting, or whiteness. Concrete will lose marks, reduce quality compared to the original design, This leads to later consequences such as cracked floors, roofs, water infiltration, nuisance and costly repairs, as well as damage to the concrete. affect the structure and quality of the whole project.

The concrete surface is cracked because of not curing the concrete properly

Therefore, "prevention is better than cure", absolutely must not ignore concrete curing.

Proper concrete curing process

Vietnam maintenance standards

Concrete that wants to be cured properly should be in compliance with the curing standards specified in the specification TCVN 8828:2011. It can be cured by covering the surface with damp material and watering continuously to keep it moist.

According to TCVN 8828:2011, our country's territory is divided into 3 typical climate zones, namely A, B, C with geographical boundaries, season names and time of year specified as follows:

Climatic zone	Geographical location	Season name	Time of year (in months)
Region A	From Dien Chau district (Nghe An) onwards	Wet rainy season	April-September
		Dry season	October – March
RED region	East Truong Son (From Dien Chau to Ninh Thuan)	Dry season	February-July
		Rainy season	August-January
Area	The rest (Including the Central Highlands and the Southern Delta)	Dry season	December – April
		Rainy season	May-November

Also according to this standard, the curing process of concrete is divided into two stages: the initial curing phase and the subsequent curing phase. These two stages are carried out continuously, successively without interruption; from finishing the concrete surface until the concrete has reached its ultimate curing strength.

Initial maintenance phase

• After the concrete is finished, it is necessary to immediately cover the open surface with moistened materials (such as sawdust sand, rice straw, water hyacinth, etc.). At this time, do not apply mechanical force and do not water directly on the surface to avoid damaging the concrete surface. When necessary, water the surface of the damp mulching material.
• It is also possible to cover the concrete surface with water-insulating materials such as nylon, canvas or spray a film forming agent to prevent water from evaporating. When a film forming agent is used, spraying should be carried out according to the manufacturer's instructions. Or misting to spray water into a mist on the concrete surface without covering the surface.
  

  Covering with nylon to cure concrete in the first stage

• The coating of concrete during the initial curing phase of concrete is mandatory when construction in conditions of rapid water loss, such as extremely dry weather or intense sunlight, etc. to ensure limited water loss and avoid surface cracking. concrete.
• The moisture retention of concrete during the initial curing period lasts until the concrete attains a certain value of compressive strength, so that water can be applied directly to the concrete surface without causing damage.
• The time to reach this intensity in the wet and rainy season in region A and in the seasons in regions B and C is about 2.5-5 hours, in the dry season in region A is from 5-8 hours depending on the nature. of concrete and weather characteristics.

The next maintenance phase

• Determined when the test water is applied to the concrete surface without causing damage, the next stage of curing can be carried out.
• This is the period when watering is required to keep all exposed concrete surfaces moist until the curing process stops.
• Concrete curing time is decided according to each item such as floor, beam, column... and development strength of concrete block. Usually, when concrete is about 3 days old, they will see the strongest development, reaching about 40% of strength. After 7 days, it reached 60% and reached 100% after 28 days. Two milestones that need special attention are the first 3 days and the next 7 days.
• In the first 7 days, conduct watering every 3 hours, at least once at night. In the following days, it needs to be watered 3 times a day. From the 14th to the 18th day, water 3 times a day. Maintenance must be maintained regularly within the first 1 week.
• Note that in the first 2 days after pouring concrete, if it rains heavily, it must be covered to avoid rainwater falling on the concrete surface.

Some notes when curing concrete

• Keep the formwork in place: The formwork is very effective in maintaining moisture and water for the set concrete. Water can be sprayed directly into the formwork to increase humidity.
  

  Keeping the formwork intact is a simple way to maintain concrete

• Only remove the formwork when the concrete structure has reached enough material strength to stabilize the structure. Normally, after pouring concrete under normal conditions (20-30 degrees Celsius), the formwork can be dismantled after 4 weeks. However, if conditions permit, the longer the better. There have been cases where removing the formwork too soon caused the structure to collapse, causing serious accidents. If it is imperative to remove the formwork early, it is advisable to continue to support the beams, floors and main beams with wooden or metal struts.
• When spraying water to keep the concrete moist, note that it must be sprayed evenly, spraying small water jets continuously at a constant cycle. It should be noted that a small spray of water that provides frequent moisture is better than a rush, but there is a dry interval between two sprays.
• To avoid erosion or layering of the material, it is recommended to use a fine-grained nozzle to spray water.
• Water used to irrigate concrete surfaces must meet the requirements of TCVN 4506:1987. It is also possible to use river water, lake water without impurities causing damage to concrete to cure concrete.
• For roof truss concrete with a relatively favorable plane, the optimal solution is to build beige bricks to soak in water. For foundation concrete, it can also be soaked in water when it is hot in the sun to achieve the best quality.

Concrete roof deck can be soaked in water for curing

Above, we shared with readers the importance of concrete curing and proper concrete curing process. Hope readers can apply it to concrete maintenance to make your house sustainable and of the best quality!