Some Common Causes of Concrete Cracking

A common saying in concrete construction is that concrete will always crack, but the formation of cracks on concrete structures is a matter that should concern property owners. This is because, if the cracks are not repaired in good time, they may result in serious and costly structural integrity issues. Therefore, it is in your best interest as the owner of a concrete building to know what causes concrete to crack so you can take steps to control the problem. Though cracks may form in concrete because of several factors, here are some of the more common reasons behind the problem.

Drying shrinkage

Concrete material is made by mixing sand and cement with water. Once the concrete has been installed, it is allowed time to harden and dry up. As hardened concrete is drying, it significantly shrinks and thus reduces in volume. The volumetric change leads to cracking. One major factor that impacts the drying shrinkage attributes of concrete is the volume of water in the concrete mix. Generally, the higher the water content, the greater the extent of shrinkage. Minimise water content of the mix by maximising the volume and size of coarse aggregate. It is advisable to use low-shrinkage aggregate. An effective way to manage drying shrinkage and influence the location of cracks is to strategically place construction joints on the concrete.

Thermal shrinkage

The heat of hydration that cement typically generates causes concrete temperatures to increase during the curing process. The temperature peaks may also vary depending on other factors, such as solar heat and installation of a waterproof curing membrane. As hardened concrete starts to cool to lower temperatures, the cooling process leads to thermal contraction of the material, which in turn, results in cracking. One way to help minimise thermally induced cracking is to increase the tensile strength of concrete.

Freeze-thaw cycling                                           

There are two basic forms of damage caused by freezing and thawing. The first is surface scaling due to freezing due to the use of de-icer chemicals, and the second is internal cracking due to freeze–thaw cycles. The freezing of water and the subsequent expansion leads to deterioration of the concrete material. As the water freezes and expands, osmotic pressure mounts in the pores of the concrete. Water travels to places where it can freeze and ice forms in crevices, which tend to open wider and form cracks. Ensuring a proper mix is essential to preventing cracking occurring due to freezing and thawing cycles.

For more information, contact a concrete crack repair company.

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