Is it Normal for Concrete to Have Small Cracks?

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 reason your fresh concrete can crack. 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. A well-made concrete structure should not develop structural cracks quickly. However, fine cracks can be expected. As the tile loses moisture during curing, it becomes a little smaller.

As the concrete shrinks, the slab may crack to relieve stress. Shrinkage cracking is common and can occur as soon as a few hours after the tile has been poured and finished. They are generally not a threat to the structure. Plastic Shrinkage Cracks are probably the most common reason for early cracks in concrete. When the concrete is still in the plastic state (before hardening), it is filled with water.

This water takes up space and makes the slab a certain size. Because concrete is a very rigid material, this shrinkage creates stress on the concrete slab. As the concrete shrinks, it drags through its granular subbase. This impediment to their free movement creates tension that can literally separate the slab.

When the stress becomes too great for the now-hardened concrete, the slab cracks to relieve stress. Especially in hot climates, shrinkage cracks can occur as soon as a few hours after the tile has been poured and finished. Concrete cannot contract more than the object on which it is poured, and this causes enough stress to crack the concrete (see figure). If the concrete is placed over a poorly compacted trench, the vacuum created by the subsidence can cause a crack in the unsupported concrete slab (see Figure). Because the flexural strength of concrete is lower than its compressive strength, concrete bends to its breaking point. For a narrow crack like this, you can use a self-leveling concrete crack filler to seal the crack before painting or finishing the surface.

Because concrete cannot contract around a corner, stress will cause the concrete to crack from the point in that corner (see Figure). A reputable local concrete driveway professional will know the best way to keep a concrete slab in good condition for optimal curing. As concrete expands, it pushes against any object in its path, such as a brick wall or adjacent concrete slab. Instead, cover the concrete with an insulating plastic sheet or even straw to trap moisture and help the concrete cure at an even rate. While shrinkage cracks can appear on the surface within hours of pouring concrete, it takes a full month for new concrete to fully settle. In addition to these traditional curing methods, concrete additives and curing compounds can help concrete cure faster and resist cold. If a tree is too close to a concrete slab, growing roots can lift and crack the concrete.

Big D Ready Mix Concrete has been serving customers in the Dallas, TX area since 2002, with more than 400 utility mixes, heavy duty wall mixes, exposed aggregate mixes, flexural strength mixes, stamped concrete mixes, fluid fill mixes, grout mixes and mixes for trailer pumps. If your concrete is a little older, a concrete repair professional can help you fix the cracks. Repairing a fine crack in a concrete structure involves filling the space with a material that adheres well to the concrete, restores its original appearance, and prevents liquids from penetrating inside the structure and staining the concrete. Once the concrete has fully cured, you can also consider using a concrete sealing compound to improve appearance and reduce cracking.