Does Concrete Always Crack? An Expert's Guide to Common Cracks in Concrete

When you spot a crack in a concrete slab or wall, it's natural to worry that something has gone wrong. But the truth is that some cracks are unavoidable due to the structure of the surface. In this article, we'll explain 6 of the most common types of cracks in concrete and how to prevent them. It's natural to worry about cracks in freshly poured concrete.

The truth is that some cracks are inevitable due to the structure of the surface. Let's dive into the reasons why your fresh concrete can crack. Cracks in concrete are common and develop when stresses in concrete exceed its strength. Cracks are usually caused by normal shrinkage of concrete as it hardens and dries.

Concrete cracks can range from being non-structural and unsightly, to being detrimental to the structural integrity and safety of a building. Tight cracks are common in concrete slabs. In general, if the crack is stable and does not leak water, it does not indicate a structural problem. In most cases, these are shrinkage cracks that form when concrete has cured.

Even if concrete cures slowly as described above, it is possible that a large slab, such as a patio or sidewalk, will still crack as a result of concrete shrinkage that occurs as temperatures change and water is consumed in the hydration process. Due to the natural movement of the soil underneath, concrete slabs eventually crack. This is why control joints are crucial. These intentional weaknesses are cut into the slab to about a quarter of its depth to anticipate and direct any future cracks. Cracks will most likely occur in these weaker parts.

Concrete shrinks as it cures due to moisture loss in concrete. If the concrete were free to shrink, it would not crack, but all concrete structures are somewhat restricted from shrinking and therefore, reinforcement joints and crack control are provided to minimize cracking. You can cut them into the concrete slab the day after pouring them with a circular saw equipped with a concrete blade. The key point to understand in relation to cracking is that water is a certain percentage of the concrete mix. These temperature variations exist because the internal temperature of the concrete slab rises and falls slowly, due to the exothermic reaction of the concrete, while the peripheral temperature of the slab cools rapidly due to the ambient temperature. Certain cracks in the concrete can best be repaired by targeted injection of the appropriate material adapted to the diagnosis of the individual crack, followed by a suitable concrete protective coating.

Unless the structural tolerance level is exceeded, early aging cracking formed by early thermal shrinkage is not considered to affect the overall safety of concrete structures. Adding water to ready-mix concrete increases the likelihood of segregation and excessive bleeding, which will make the concrete surface porous, weak, and prone to cracking. When properly installed, concrete is one of the most durable and long-lasting products you can use in your home. Carbonation occurs when carbon dioxide from the air penetrates concrete and reacts with hydroxides, such as calcium hydroxide, to form calcium carbonates in the presence of water. In order to be able to pour and work with it, almost all concrete contains more water than is necessary for the hydration of the cement. The selection and use of appropriate materials with good construction practices reduces the occurrence of shrinkage and resulting cracks, thus improving service life and reducing life cycle cost of concrete structures. When non-crystalline silicon dioxide (mainly originating in Portland cement) reacts with alkali hydroxide in concrete or alkalis present in environment such as sea spray or groundwater, reaction forms an alkali silicate gel that swells as it absorbs moisture from cement pore surrounding solution in concrete or environment. An example of an external restraint is when concrete is poured onto a pre-hardened base or adjacent to similar elements without provision of an expansion joint.

Air and concrete temperature, wind speed, heating and drying action, and relative humidity play an important role in rate of moisture evaporation of set concrete. Reinforcement sizing is essential for service life and therefore for structural integrity of concrete. If your concrete is a little older, a professional can help you fix any cracks.