Cracks in Concrete: Common Causes and Solutions

Cracks in concrete are a common occurrence, and they can be caused by a variety of factors. Normal shrinkage of concrete as it hardens and dries is one of the most common causes of cracking. Placing excessive amounts of weight on top of a concrete slab can also cause cracking. When you hear that a concrete mix has a strength of 2000, 3000, 4000, or more than 5000 PSI, it refers to the pounds per square inch that would be needed to crush that concrete slab.

It's natural to worry about cracks in freshly poured concrete, but some cracks are inevitable due to the structure of the surface. Let's dive into the reasons why your fresh concrete can crack. There are three main types of daily cracking: shrinkage cracking, diagonal cracking, and horizontal cracking. Shrinkage cracking occurs when concrete is placed in its liquid form and then dries out.

Diagonal cracks can appear anywhere along the height of the reinforced concrete and are usually caused by insufficient cross-section, inadequate bearing capacity of columns, and inadequate reinforcing steel. Horizontal cracks can cause a substantial reduction in the shear strength of the column. Split cracks appear in the form of short, parallel vertical cracks in reinforced concrete columns and are usually caused by poor concrete quality and insufficient steel reinforcement. Corrosion cracks appear mainly along the reinforcement line of the concrete column due to improper joints between concrete and steel bars and possible reinforcement corrosion.

If your concrete is a little older, a concrete repair professional can help you fix the cracks. In addition, concrete poured in mid-summer will have more cracks than concrete poured when it is colder. Control joints are designed to weaken concrete in certain areas so that it cracks in a straight line in these spaces. If a structural contractor drives a piece of heavy equipment loaded with wood onto a 4-inch thick concrete slab, it can crack green (not fully cured) concrete.

Covering the slab with an insulating plastic sheet or even straw can help trap moisture and help the concrete cure at an even rate. Site preparation, proper mixing and good concrete finishing techniques can help reduce the appearance of cracks and produce a more aesthetically pleasing project. Once the concrete has fully cured, you can also consider using a concrete sealing compound to improve appearance and reduce cracking. Concrete Decor is a valuable source of information, ideas, product news and training relevant to commercial and residential work in decorative concrete and related specialties. Steel springs can also be used to help prevent cracking as the concrete contracts. This means that as the concrete contracts, the steel springs help the concrete to contract down the ground on which it is seated, preventing cracks from forming or, at least, separating.