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Why Does Concrete Crack?

written by: Suvo • edited by: Lamar Stonecypher • updated: 8/18/2010

Cracks are one of the most common defects in concrete. This article will discuss the four main reasons for concrete cracking and how concrete surface cracking can be avoided.

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    Concrete Defects in Civil Engineering

    The Delhi Metro railway bridges in India are probably one of the most discussed civil constructions for developing cracks. Various types of cracks are quite common in civil construction. Most of the time cracks could be avoided by using proper concrete mix proportions. Following are the four major reasons why cracks develop in concrete:

    • Excess water quantity: Most often time Portland cement is used for construction. Portland cement, being a hydraulic type of cement, needs water for developing strength. Also, water increases the flowability of the cement concrete and thus increases the ease of its use. But when the concrete dries and hardens, the excess water from the concrete evaporates and the concrete shrinks. As a result of that, cracks develop in the concrete.
    • Too dry weather: After the wet concrete mix is spread, it takes a few weeks to complete the whole hydration process. This hydration process gives strength to the concrete but also needs sufficient water. If the concrete does not get sufficient water for hydration, it tends to develop cracks.
    • Incorrect selection of cement: Cement comes in different grades as per the strength requirement of the concrete. In case you have selected wrong or weak cement, your concrete won’t have enough strength and will develop cracks.
    • Control Joints: Control joints are planned cracks. Control joints gives room for shrinkage and thus control joints help in avoiding random cracks. Typically a 4” thick concrete slab should have the concrete joints around 8-12 feet apart.
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    Other Common Factors in Concrete Surface Cracks

    There are various types of concrete cracks. Most of time using the correct proportions of the ingredients and workmanship could reduce concrete surface cracking defects.

    Apart from the discussed causes of the concrete cracks, sometimes the quality of the ingredients and the weather also plays an important role in preventing concrete defects. For example, if the concrete laying surface is too cold or too hot then chances are that the concrete will produce surface cracking.

    Similarly, if the water used for the construction is too hard to drink, then it is better to make it soft and drinkable before using it for concrete making.

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    Related Reading

    Concrete Road vs Asphalt Road: Asphalt roads score better in some areas over concrete road, and that is the reason why they are replacing all concrete roads with asphalt. Having said that, concrete roads also have some major advantages over asphalt roads. Learn about the comparison of concrete paving and asphalt paving in this article.