Concrete, like other construction materials, can deform in response to changes in temperature or moisture. Cracks that do not compromise structural integrity are usually not dangerous.
Defects in concrete structures can develop both during and after construction, and they can manifest themselves in a variety of ways. Concrete cracks are not all the same. When choosing on the best approach to repair the cracks, it is vitally helpful to know which type you are dealing with.
There are many different types of cracks, with the following six being the most common:
Concrete cracking is primarily caused by shrinkage. These cracks appear in concrete while it is still in the plastic state. When concrete reaches this stage, it still contains a significant amount of water. When the water eventually evaporates from the slab, it leaves large voids between the solid particles. These voids weaken the concrete and make it more prone to cracking. This type of cracking is common and is known as “plastic shrinkage cracking.” Shrinkage cracks occur while the concrete is still curing and can be reduced or avoided by using proper joint placement.
If the ground beneath the slab is not properly flattened, a portion of the concrete begins to sink. These are known as settlement cracks, and they can also appear as a random crack above areas where the soil was uneven after the concrete was poured. For example, when a large tree is removed, the area where the roots were is left empty, resulting in softening of the ground. Another example is when utility companies dig trenches to install pipes, lines, and other infrastructure. Typically, this type of crack is continuous.
As we said in the beginning, concrete can shrink or expand as a result of temperature and moisture changes. Temperature differences within a concrete structure can be caused by different parts of the structure losing heat of hydration at different rates, or by weather conditions cooling or heating one part of the structure to a different degree or at a different rate than another. When the temperature returns to normal, the slab returns to its original shape. However, this shape change frequently results in the formation of heaving cracks. Contraction joints in concrete slabs should be used to control changes in concrete volume caused by temperature or moisture.
Concrete cracking can be caused by weather conditions such as freezing and thawing, wetting, drying, heating, and cooling. The most common type of weather-related physical deterioration is damage caused by freezing and thawing. The lowest effective water-cement ratio and total water content, as well as durable material and adequate air flowability, provide the best protection against freezing and thawing in concrete. Before exposing to freezing temperatures, it’s also important to cure adequately.
Crazing cracks are characterized by the formation of fine random cracks in the concrete because of surface layer shrinkage. This is caused by the concrete surface rapidly drying, especially if the surface was exposed to low humidity, high air temperature, or summer heat during the concrete mix’s setup. These cracks have an irregular shape and resemble hexagons. They are no deeper than 3 millimeters. Apart from being unsightly, these cracks are usually harmless.
Corrosion cracks can form because of rusting steel used to support the concrete. Corroding reinforcement is also common in older concrete structures where too much calcium chloride was added to the concrete mix to speed up the hardening process. Corrosion causes internal pressure as it accumulates in thickness. The pressure causes the concrete to crack near the steel, which leads to more extensive cracking over time as the rust accumulates until the concrete begins to break away from the reinforcing steel bars, exposing the corroded reinforcing steel rods.
Cracks can also form as a result of poor concrete installation or overloading the concrete surface. When you notice a crack in a concrete slab or wall, it’s logical to be concerned. You may be wondering whether this is a structural issue or merely an aesthetic concern. We discussed the six most common types of concrete cracks in this article. Understanding each of these types enables us to take the necessary steps to repair the cracks and avoid larger issues in the future.