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In this article, we will discuss crazing concrete.
Crazing is a formation of a network of tiny random cracks on the surface of concrete formed due to the shrinkage of the surface layer.
Crazing cracks are very fine, surface cracks that resemble spider webs or shattered glass. When the top of a concrete slab loses moisture fastly, crazing cracks will likely be observable. Crazing cracks are not a structural concern as it doesn’t affect the durability of concrete.
Usually, Crazing concrete is known as spider cracking or map-pattern cracking. Crazing concrete is a hexagonal shape that occurs on the surface of the concrete that appears as a spider web.
Cracking is a very familiar issue in structures made out of concrete. To be precise, it is very difficult to encounter a crack-free concrete surface in the whole world.
Premature or Early age cracking of concrete surface is the mutual effect of so numerous things occurring at the exact time, be it a poor composition of the mixture.
inadequate exposure to sunlight, improper hydration of the concrete, and following not-so-appropriate curing conditions or techniques.
The difference between cracking and crazing is,
Cracking is identified by the spectator visually easily and via physical touch. It’s also straightforward to comprehend that the material has been weakened when cracks are available.
Crazing is internal fracturing without a change of surface texture.
1. Crazing Concrete
If the crazing concrete is assumed to be originated, then it majorly gets originated within the week of the settlement of the concrete mixture.
When it is left neglected then these cracks widen up with time and must be cured. The visible cracks are typically 2 mm to 3 mm deep.
Crazing Concrete does not affect the durability or the strength of the structure but it does glance bad visibly as these cracks are sometimes extremely considerably remarkable.
In any case, if these cracks are not cured for a lengthier duration of time then, they may grow into larger cracks that can cause water or moisture to seepage deep into the structure outcoming in the corrosion of metals.
Crazing concrete may look undesirable and those cracks can contain dirt or dust but crazing does not have any extreme importance for the structure.
A few more cracks that are identical to craze cracking are plastic shrinkage cracks and drying shrinkage cracks. Plastic shrinkage cracking occurs when concrete is still plastic.
These cracks are deeper and wider. They are also caused by drying, as wetness at the surface level disappears. The other one is the drying shrinkage cracks, majorly happening after a concrete slab possesses hardened. The loss of water in the concrete mixture itself is the major causality of it.
2. Causes of Crazing Concrete
There are different reasons that can result in crazing concrete. Crazing can appear on uncovered surfaces as well as on concrete surfaces that are in direct contact with the formwork.
The primary cause is the shrinkage of the surface, due to any environmental, physical, or artificial element.
a. Lack of Curing
When concrete is given to dry with inappropriate curing, the evaporation of water from the surface of the concrete evolves rapidly as the correct amount of water is not provided to it. In this phase, the dried–out concrete soaks more water. Hence causing the crazing concrete surface of the concrete.
These situations happen when concrete is placed to try in areas, where there is low humidity, fast airflow, and direct sun exposure with non-uniform water spread across the surface. Most of the time it happens because of the negligence of the manpower concerned in that project.
b. More Water-To-Cement Ratio
The use of surplus water may also generate crazing. The surplus water supplied to the concrete determines the top of the surface and forms a thin layer of water.
Later, this surplus water dries out and finally reveals the characters of crazing concrete. Balancing the proper quantity of water with respect to the mixture of concrete mix is very crucial work.
c. Unskilled Manpower
Poorly skilled manpower is also an element that guides crazing concrete. Regular actions of a trowel to settle down the concrete fast sometimes obtain the cement to the surface. Hence, resulting in water bleeding. This smallish poor practice also generates cracks to occur on the surface.
d. Employing Dry Cement for Finishing
In order to obtain better finishing. Many artisans sprinkle dry cement over the surface of the concrete which still has some moisture, this causes the concrete to dry up really fast and also results in the development of cracks.
e. Excessive Vibrations
Offering more vibrations while concrete is dropping down gets cement slurry to the top, dropping metal and gravel at the bottom. Once the cement at the top dries up, it makes crazing concrete.
Many new-age concrete mixture vibrators can be assigned to a specific RPM (Rotation Per Minute) to countermeasure the reason for crazing concrete.
Earlier, when a manual effort was applied to set the concrete rather than electric vibrators, then there were very high probabilities of generating crazing on the concrete’s surface, but currently, modern tools have assisted in evading this to a very good extent.
When the region is not so well ventilated and the concrete is given to dry, in that case, concrete acts with carbon dioxide in the air or carbon monoxide emitted from machinery or vehicles.
It generates shrinkage of the surface layer guiding to cracks that start to show up as soon as the concrete begins settling down. This chemical reaction usually occurs in untidy, congested, and ill-ventilated places.
There are other reasons too such as if the mortar employed in the construction is too rich or wet and even if no good curing is accomplished. This may drive shrinkage. When too fine sand is employed and rendering or plastering is accomplished after a long interval of the casting of concrete, then also it forces crazing concrete to occur.
3. Treatment of Crazing In Concrete
The best practice is to glaze the surface of concrete regularly, to stop or decrease the risk of cracking over the concrete surface. Using epoxy and silica sand over the concrete slabs provides a monolithic impression to it which is crack-free as well. This definitely changes the look of the surface and also improves the color.
Moreover, afterward, the additional surface can be terminated with the use of any resurfacing product. An alternative very beneficial treatment that is very practical too is, polishing the surface where cracks are observable.
Polishing ultimately grinds the upper surface layer where the crazing pattern gets, to clear the cracks which are usually just 2-3 mm deep.
One can also employ curing monomolecular compounds on the surface, which controls the rapid evaporation of moisture from the cement and assists in combating the crazing concrete.
If crazing is not so well-known, then grout can also assist in filling those tiny cracks.
Read Also: Two-Way Slab
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