Cracks in concrete are a common occurrence and develop when the stresses in the material exceed its strength. This is usually caused by the normal shrinkage of concrete as it hardens and dries. Tight cracks are often seen in concrete slabs, but they do not necessarily indicate a structural problem. In most cases, these are shrinkage cracks that form when the concrete has cured. It's natural to worry about cracks in freshly poured concrete, but some of them are unavoidable due to the nature of the surface.
Let's take a closer look at why your fresh concrete can crack. You can expect shrinkage and cracks in the slab base, and these are very common. They generally do not compromise the structural integrity of the home. Due to humidity, things like hardwood floors, moldings, and wooden frames can shrink and acclimate to lower indoor humidity.
Similarly, with temperature changes, expansion and contraction can occur daily and seasonally. Cracks in concrete are often misunderstood. When a homeowner sees a crack in their slab or wall, especially if the concrete is relatively new, they automatically assume something is wrong. This is not always the case. Some types of cracks are unavoidable. The best thing a contractor can do is try to control cracking.
This is done by properly preparing the subbase, ensuring that the concrete is not too wet, using reinforcement where needed, and properly placing and spacing crack control joints and expansion joints. However, cracks sometimes occur despite the precautions taken. Once the concrete has fully cured, you can also consider using a concrete sealing compound to improve appearance and reduce cracking. Ambient temperatures above 90 degrees Fahrenheit and the lack of a protected environment for concrete placement and finishing (enclosed building) can contribute to the difficulty of producing quality concrete. Shrinkage cracks cannot always be prevented, but they can be controlled by drawing planes of weakness to establish the direction of cracking when shrinkage occurs. Understand what your contractor is doing with respect to each of the items listed above and you will get a good concrete job.
It's frustrating to spot fine cracks, especially if you've just paid for a new driveway, concrete slab, walkway, or garage floor. Pouring concrete when conditions are too high (above 77°F) (if any) means that some of the water that hydrates the concrete evaporates rather than bonding in the chemical reaction, increasing the chances of shrinkage cracking and creating a weak slab. Unless the structure in question allows movement of its members without the development of excessive stresses, extensive cracks can often occur. When properly installed, concrete is one of the most durable and long-lasting products you can use in your home. By using the procedures outlined here and exercising proper care, you will get the best performance out of your Holcim concrete. This is done by cutting grooves one-third the thickness of the slabs, and is done as soon as the concrete is hard enough to withstand damage from the saw. A good rule of thumb for 100mm thick residential concrete is to place joints so that they separate the slab into approximately equal square sections, with no joint being more than 3 meters from the nearest parallel joint. The phenomenon of cracking is complex and depends on several factors such as drying speed and amount, drying shrinkage, tensile strength, tensile deformation, creep, elasticity, degree of restraint and other factors.
The danger in both cases is that cracks can channel moisture and cause damage if left unchecked. Control joints create a weak spot in the slab so that when it contracts it cracks at this point rather than randomly along its surface (see figure). Consequently, both designers and contractors must inform homeowners that it is normal to expect some amount of cracking and curling in each project; this does not necessarily reflect negatively on either floor design or construction quality (Ytterberg1987; Campbell et al.).Reviewing types of cracks in floor slabs from our previous article will give you a better idea of damage range and distinction between cosmetic and more serious cracks in concrete.
