What Causes Cracks in Concrete Slabs and How to Avoid Them

Cracks in concrete slabs are a common occurrence, and they can be caused by a variety of factors. The two most common causes of premature drying are high slump mix and cold joints. High slump mix is when too much water is added to the concrete mix, which weakens it and makes it more prone to cracking. Cold joints occur when a section of concrete has hardened and then another section is poured next to it.

When concrete is poured, it shrinks as it hardens and dries. This shrinkage can cause cracks if the stresses in the concrete exceed its strength. Additionally, if heavy equipment is driven on a 4-inch thick slab of green concrete (not fully cured), it can cause the concrete to crack. Another cause of cracking is plastic settling.

This happens when the concrete is still in its plastic state and the water takes up a lot of space, increasing the size of the slab. If there are sublayers that are not tightly compacted, then when the concrete is poured onto them, the weight can cause these areas to fall out and create cracks. Temperature differences between the concrete structure and its environment can also cause cracking. If one part of the concrete is colder than another, it will shrink more than the hotter part, leading to cracking.

Finally, crust cracks can form during the stamping process, which is used to add texture or pattern to concrete surfaces. These cracks can be troweled into the concrete or thin strips of plastic can be embedded in the fresh concrete to weaken it. The best way to avoid cracks in concrete slabs is to use less water in the mix and ensure that all sublayers are tightly compacted before pouring the concrete. Additionally, contractors should avoid driving heavy equipment on green concrete and should be aware of temperature differences between different parts of the structure.