Cracks in concrete are a common occurrence, but they can be alarming to homeowners. While 95% of cracks are harmless, it's important to understand the different types of cracks and when they may be a sign of a more serious issue. Cracks can be caused by normal shrinkage as the concrete hardens and dries, or they can be caused by external factors such as heavy vehicles or nearby trees. In some cases, cracks can be prevented by properly preparing the subbase and using reinforcement where necessary.
In other cases, cracks may need to be filled with an epoxy layer or reinforced with steel cables. Shrinkage cracks are the most common type of crack in concrete and are caused by the normal drying process. These cracks are usually small and harmless, but they can sometimes indicate that the concrete was poured when conditions were too high. If a crack line is more or less straight and extends into the foundation walls or at right angles to them, it may indicate that the foundation has settled.
Reentrant corners and circular objects in the middle of a slab can also cause plastic shrinkage cracks. If you see a pattern of cracks or rust on the garage floor that looks like the cracks are 12 to 24 inches apart in one or two directions, it may be an indication that the rebar was placed too high and does not have enough concrete to properly cover it. An unreinforced concrete slab is more likely to crack than a reinforced slab and is weaker. The best way to prevent cracking is to take precautions when pouring the concrete, such as making sure that the subbase is properly prepared and that the concrete is not too wet.
Additionally, correctly placing and spacing crack control joints and expansion joints can help reduce cracking.