The Crazing Concrete Guide from Construction World
The crazing of concrete may be unsightly and the cracks may collect dirt and dust, but it does not pose any serious structural risks. A crazing occurs when the surface layer of concrete shrinks, causing a network of fine random cracks to appear.
Concrete structures are subject to cracking very often. Concrete surfaces with no cracks are extremely rare in reality. A premature or early age cracking of concrete is the result of many factors happening at the same time, be it the wrong mixture composition or a bad construction process. It was exposed to insufficient sunlight, the concrete was improperly hydrated, and the curing conditions were not appropriate.
These cracks may become bigger if not treated for a long time, which can cause water to seep into the structure and cause corrosion of metal. If these cracks are not treated for a long time, they could become bigger and cause corrosion to occur.
Possible reasons for Concrete Cracks
Here are the possible reasons for Concrete Cracks:-
Define Crazing of Concrete
Crazing concrete is often called spider cracking or map pattern cracking because it appears in a hexagonal pattern, similar to a spider's web, on the surface. Typically, if crazing concrete is expected to develop, it typically develops within a week of settlement.
How Cracks occurred in Concrete?
Cracks caused by shrinkage and drying are similar to craze cracking. When concrete is still plastic, it is prone to shrinkage cracks. As moisture evaporates from the surface level, these cracks become deeper and wider.
Cracking is primarily caused by shrinkage of the surface due to environmental, physical, or artificial factors. Besides drying shrinkage cracks, which normally occur after concrete slabs have hardened, there are also temperature cracks. This is primarily caused by the loss of water in the concrete mixture.
Crazing Concrete Causes
The cause of concrete crazing can vary depending on the surface. For example, exposed surfaces or surfaces with direct contact with formwork can cause concrete to crack. There is no deterioration in the durability or strength of Crazing Concrete, but it does detract from the appearance, as these cracks are often noticeable.
Due to improper curing of concrete, water evaporation from its surface becomes rapid when left to dry as the right amount of water is not applied. Concrete that has dried out absorbs more water in this phase, resulting in the concrete surface crazing.
Concrete is set to try in areas that are low in humidity, have fast airflow, and are exposed to direct sunlight with non uniform amounts of water. It is typically the result of negligence on the part of the workers involved in that project.
Excess Water Cement Ratio
It is also possible to cause crazing by using too much water. A thin layer of water forms at the surface of concrete when excess water is supplied. Over time, this excess water dries out and eventually causes the concrete to crack. It is extremely important to balance the right amount of water in the concrete mix.
Too Much Vibration
Concrete slurry rises to the top when vibration is given while it is settling, leaving metal and gravel at the bottom. Crazing concrete occurs when the cement on top dries up. Modern concrete mixture vibrators can be set to a specific RPM to counteract concrete crazing.
When concrete was set using a manual effort instead of electric vibrators, crazing was very likely to occur on the concrete's surface. However, today's modern tools have greatly reduced this risk.
A well ventilated area and an area that is left to dry for long periods can cause concrete to react with the carbon dioxide in the atmosphere or with the carbon monoxide released from machinery.
As soon as the concrete settles down, cracks begin to appear as a result of the shrinkage of the surface layer. Untidy, congested, and poorly ventilated places are often the scene of this chemical reaction.
Poor Skilled Labor
Concrete can also craze due to the lack of mason skills. When a trowel is used frequently to settle down the concrete fast, the cement can sometimes come to the surface. Therefore, water bleeding occurs as a result of this practice, causing cracks to appear on the surface.
Excess Mortar & Sand Use
If the mortar used in the construction is too rich or too wet, as well as not properly curing, there is a possibility of shrinkage. It is also more likely to cause crazing concrete to appear when too fine sand is used or render or plaster is done after a long period of concrete casting.
Solution of Crazing Concrete
Temperature & Moisture Checking
In order to prevent concrete from crazing, it must be cured. Temperature and moisture are necessary for curing in layman's terms. Ensure that all is well with the concrete so that the hydration process goes smoothly and is followed to ensure crack free results.
By using damp clothes or fabrics to retain moisture, keep the surface wet most of the time. To prevent concrete from cracking, it is sufficient to supply it with adequate water for two to three days.
If concrete is left to dry out, fine sand or dry cement should not be sprinkled over it. Due to the fact that low moisture cannot bind the cement particles properly, dry cement or sand absorbs all the moisture, resulting in cracks.
To get more details, watch the following video tutorial.
Video Source: Brendan Hasty
Right Water Ratio to Slump
Reducing trowel use and avoiding steel float whenever possible. Air entrained concrete with a moderate slump may be a good choice. Crazing is less likely to occur if concrete is exposed to air entertainment. This will reduce the rate of bleeding in concrete.
A slump with enough water in it can provide a crack free surface when there is sufficient steadiness in the slump.
Concrete Settling Time
When it comes to settling concrete, do not make haste. Concrete should always be allowed to settle for a few days. A uniform crack free concrete surface requires avoiding troweling repeatedly. The trowel should only be used gently after the water sheen has disappeared from the surface.
In order to improve concrete consistency, it is common to add too much water to the mixture, but it ends up becoming slurry. Avoid adding excess water to the concrete mixture to prevent this from happening.