Concrete is a popular building material that is known for its durability and strength. However, it is not immune to cracking. When concrete shrinks during the hydration period, the stresses generated by this process are relieved by cracking in the concrete mass. This can be a problem if the concrete surface is subject to water intrusion, is exposed to view, or both. In these cases, cracking can compromise the appearance of the concrete and even weaken its structural integrity.
In structural concrete, cracking is expected, but it can be reduced through careful planning and attention to the design of temperature reinforcement, mix design, and placement and curing procedures. The ideal is to control the cracking so that it occurs in a location where it is acceptable from an aesthetic point of view and can be sealed against moisture intrusion.
Unfortunately, the most common approach to crack control is to ignore it and hope for the best. This is not a viable solution, especially in exposed concrete work, where unsightly cracks can detract from the visual appeal of the surface. Ignoring cracking can lead to problems such as water penetration, which is a common cause of call backs in construction projects.
The best way to control cracks in concrete is to plan ahead and take a proactive approach. One effective method is to create a vertical weakened section in the wall every 8 to 12 feet apart, which allows the shrinkage stresses to be relieved at the weakened joints and induces a crack in a controlled location.
Crack inducing devices, when positioned inside the form and concrete is cast around them, act to weaken the concrete and guide cracking into a pattern predetermined by the design. If the design calls for flush, butt form panel joints on the concrete surface, the crack control devices can be installed in line with the joint seam, which will transfer the joint line onto the concrete surface and make the crack part of the architectural design.
In addition to using reveals or crack inducing devices, cracking can be further controlled by interrupting 50% of the non-working or temperature reinforcing steel. Crack control materials such as wood, neoprene, or polyethylene reveals can also be used to direct cracking into a controlled location.
In conclusion, controlling cracks in concrete is an important aspect of construction that can have a big impact on the appearance and durability of the final product. By planning ahead and taking a proactive approach, it is possible to control cracks and ensure that the concrete surface looks great and performs well for years to come.