What Is Crazing Concrete and Why Does It Happen?

What Is Crazing of Concrete?

Often known as spider cracking or map-pattern cracking, Crazing concrete is a hexagonal shape that appears on the surface of the concrete that resembles a spider web.

Cracking is a very common problem in structures made out of concrete. To be precise, it is very rare to find a crack-free concrete surface in the real world.

Premature or Early age cracking of concrete surface is the mutual effect of so many things happening at the same time, be it a bad composition of the mixture. Inadequate exposure to sunlight, improper hydration of the concrete, and following not-so-appropriate curing conditions or techniques.

If the crazing concrete is supposed to be developed, then it usually gets developed within the week of the settlement of the concrete mixture.

When left ignored then these cracks widen up with time and must be cured. The visible cracks are generally 2 mm to 3 mm deep. To be noted Crazing Concrete does not affect the durability or the strength of the structure but it does look bad visibly as these cracks are sometimes very much notable.

In any case, if these cracks are not cured for a longer duration of time then, they may develop into bigger cracks that can cause water or moisture to seep deep into the structure resulting in the corrosion of metals.

Visibly, Crazing concrete may look unpleasant and those cracks can collect some dirt or dust but crazing does not have any severe implications on the structure.

Crazing is a development of a network of fine random cracks on the surface of concrete caused by shrinkage of the surface layer.

Some other cracks which are similar to craze cracking are plastic shrinkage cracks and drying shrinkage cracks. Plastic shrinkage cracking happens when concrete is still plastic.

These cracks are deeper and wider. They are also caused by drying, as moisture at the surface level evaporates.

The other one is the drying shrinkage cracks, normally occurring after a concrete slab has hardened. The loss of water in the concrete mixture itself is the main cause of it.

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Causes of Crazing Concrete

There are various causes that can lead to crazing concrete. Crazing can occur on exposed surfaces as well as on surfaces that are in direct contact with the formwork The main reason is the shrinkage of the surface, due to any environmental, physical, or artificial factor.

1. Improper Curing

When concrete is left to dry with improper curing, then evaporation of water from the surface of the concrete becomes rapid as the right amount of water is not supplied to it.

In this phase, the dried-out concrete absorbs more water. Hence causing the crazing concrete surface of the concrete.

These conditions happen when concrete is set 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 occurs because of the negligence of the workforce involved in that project. 

2. More Water-To-Cement Ratio

Usage of excess water may also cause crazing. The excess water supplied to the concrete settles at the top of the surface and creates a thin layer of water.

Later, this excess water dries out and ultimately shows the signs of crazing concrete. Balancing the right amount of water with respect to the mixture of concrete mix is a very critical task.

3. Unskilled Workforce

Poor skills of masons are also a factor that leads to crazing concrete. Frequent actions of a trowel to settle down the concrete fast sometimes bring the cement to the surface.

Hence, resulting in water bleeding. This small bad practice also causes cracks to appear on the surface.

4. Using Dry Cement for Finishing

In order to get 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. 

5. Excessive Vibrations

Giving more vibrations while concrete is settling down brings cement slurry to the top, leaving metal and gravel at the bottom.

Once the cement at the top dries up,  It creates crazing concrete. Many new-age concrete mixture vibrators can be set to a specific RPM (Rotation Per Minute) to countermeasure the cause of crazing concrete.

Earlier, when a manual effort was put to set the concrete instead of electric vibrators, then there were very high chances of developing crazing on the concrete’s surface, but now modern tools have helped in avoiding this to a very good extent.

6. Carbonation

When the area is not so well ventilated and the concrete is left to dry, in that case, concrete reacts with carbon dioxide in the air or carbon monoxide released from machinery or vehicles.

It causes shrinkage of the surface layer leading to cracks that begin to show up as soon as concrete starts settling down. This chemical reaction often takes place in untidy, congested, and ill-ventilated places.

There are a few other causes too such as if the mortar used in the construction is too rich or wet and even if no proper curing is done. This may cause shrinkage.

When too fine sand is used and rendering or plastering is done after a long interval of the casting of concrete, then also it causes crazing concrete to appear.

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Prevention from Crazing Concrete

As we all know that prevention is better than cure, the same goes for preventing concrete from crazing. Numerous ways to prevent crazing are discussed below. Make sure to have a look at those.

Curing concrete is very important to prevent it from crazing. Curing in layman’s terms refers to supplying a sufficient amount of temperature and moisture.

to the concrete so that all goes well and is good for the hydration process. This must be followed for crack-free results.

Try to Keep the surface wet most of the time, either by pouring the right amount of water or using damp fabrics or clothes to retain the moisture. 2 to 3 days of adequate water supply is sufficient to prevent the concrete from cracking.

It is advised to always avoid sprinkling fine sand or dry cement over the surface of the concrete which is left to dry out. The dry cement or sand absorbs all the moisture and this loss in moisture gradually gains the shape of cracks as low moisture can not bind the cement particles properly.

At many construction sites, the floors or the pavements are equipped with normal or expansion joints in order to reduce the risk of drying shrinkage. This is also not a foolproof remediation.

Restricting the excessive trowel usage. In addition, avoid the use of steel float as much as possible. Try using moderate slump air-entrained concrete. Air entertainment will help in reducing the rate of bleeding in concrete and result in less likelihood of crazing.

The steadiness in a slump with enough water in it emerges to be a good solution for a crack-free surface.  Never make haste while finishing the settling process of concrete. It is always good to allow some extra time for concrete to settle down.

Troweling, again and again, must be avoided for uniform- crack-free concrete surfaces. Once the water sheen disappears from the surface, then only the trowel should be used in a gentle manner.

One of the most common mistakes that are often observed is adding too much water into the concrete mixture for better consistency but it ends up becoming a slurry of concrete.

In order to prevent this, Do avoid the usage of excess water in the concrete mixture.

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Treatment of Crazing In Concrete

One of the best practices is to glaze the surface of concrete uniformly, to eliminate or reduce the risk of cracking over the surface concrete. Applying epoxy and silica sand over the concrete slabs gives a  monolithic appearance to it which is crack-free as well.

This indeed changes the look of the surface and also enhances the color. Moreover, later the extra surface can be removed with the help of any resurfacing product.

Another very useful treatment that is very practical too is, polishing the surface where cracks are visible. Polishing, eventually grinds the upper surface layer where the crazing pattern accumulates, to remove the cracks which are normally just 2-3 mm deep.

One can also use curing monomolecular compounds on the surface, which prevents rapid evaporation of moisture from the cement and helps in combating the crazing concrete.

If crazing is not so prominent, then grout can also help in filling those small cracks. To conclude, the crazing concrete is a very common phenomenon that depends on many factors as we have discussed in this article.

Typically, craze cracks are not fixed or repaired because they do not worsen over time. Still, There are various ways to prevent the crazing, and treating it in the right manner is also highlighted above Hope this article was helpful to you!

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