Cracks in concrete are a common occurrence, but when should you be concerned? Most cracks occur within 2-3 days of concrete placement and are usually not an indication of serious structural problems. However, there are some that may require maintenance or indicate a structural concern. It is important to understand the causes of concrete cracking and how to identify when it is serious. Placing an excessive amount of weight on a concrete slab can cause cracks.
When you hear that a concrete mix has a strength of 2000, 3000, 4000 or 5000 PSI, it refers to the pounds per square inch it would take to crush that concrete slab. Plastic shrinkage cracks are the most common reason for early cracks in concrete. When concrete is still in its plastic state (before hardening), it is full of water. As the slab loses moisture during curing, it becomes slightly smaller and creates stresses in the concrete slab.
Crazing is the development of random fine cracks on the surface of the concrete caused by shrinkage of the surface layer. Carbonation occurs when carbon dioxide from the air enters the concrete and reacts with hydroxides, such as calcium hydroxide, to form calcium carbonates in the presence of water. Alkali-silica reaction (ASR) is another cause of cracking in concrete structures near waterlines or bodies of water. Once a qualified and licensed inspector has diagnosed the cause and significance of concrete cracking, it is important that accurate repair methods are followed.
Understand what your contractor is doing with respect to each of the items listed above and you will get a good concrete job. Cracks that are identified as small and hairline (less than 0.3 mm wide) are generally considered acceptable as part of a minor slump, depending on the purpose and intent of the concrete structure, the environment in which it is placed, service life design and durability design. Metal mesh is often used as reinforcement to hold the concrete pieces together but does not prevent cracks. This will allow cracks to occur, because the concrete is shrinking around all this mesh, and the mesh may not shrink with it.
So if the concrete is poured in colder months, assuming it is placed on a good foundation, it will have fewer and smaller cracks. If a house is on a hillside and there is a living area or open space under the garage floor, then all cracks should be assessed for safety reasons. Control joints are pre-planned and pre-installed to prevent the concrete from cracking due to shrinkage during curing. The product reacts quickly with water, chasing the water present in the crack and begins to foam and expand, filling the entire crack, resulting in a strong bond with the concrete and a flexible waterproof seal that prevents future water leakage. Although early cracking may initially be considered a minor deficiency, it is advised that building owners and those responsible for maintenance appoint qualified repair contractors to properly repair these cracks as soon as possible to help prolong the life of concrete structures.
