Cracks in concrete are ruptures that can affect the structure of a building, affecting its durability, safety, and aesthetics. They significantly increase maintenance costs. Understanding the causes behind cracks and applying the appropriate preventive measures is necessary to ensure the longevity and good performance of any construction project.
External and internal factors influencing the formation of cracks in concrete
External factors
- Functional loads: The loads acting on a structure during its service life can be static, such as the building's own weight, or dynamic, such as those generated by traffic, vibrations, or wind. They exert continuous stresses on the concrete; which, if not properly evaluated from the structural design phase, could result in the formation of cracks or even progressive rupture.
- Environmental influences: Extreme weather conditions are a determining factor in the formation of cracks. Drastic changes in temperature and humidity, as well as climatic phenomena such as wind, snow, or the action of moving water, impose additional loads on concrete structures. These environmental stresses generate surface or deep cracks that weaken the material if the effect of these factors has not been considered during design.
Internal factors
- Intrinsic changes: Concrete undergoes several shrinkage processes that are one of the main causes of cracking. Plastic shrinkage occurs during the first hours after pouring, when concrete loses surface water rapidly. Drying shrinkage occurs when the concrete has hardened and loses internal water, reducing its volume. Both generate internal stresses that, if not controlled by proper curing techniques, can lead to cracking. In addition, chemical processes such as the alkali-silica reaction (ASR), where certain aggregates in the concrete react with the alkalis in the cement, causing internal expansions that lead to cracks.
- Imposed deformations: Prestressing and post-tensioning techniques, designed to improve the load-bearing capacity of concrete, can also cause cracks if not properly executed. These techniques induce internal stresses in the concrete that, if excessive or poorly controlled, generate cracks. Also, differential ground settlements, caused by uneven soil movements under the foundation, can cause diagonal cracks that directly affect the stability of the structure.
Impact of cracks on the durability and safety of concrete structures
Cracks in concrete have a critical impact on the durability and safety of the structure, as well as affecting its aesthetic appearance. By allowing the entry of external agents such as water, salts, and chemicals, cracks accelerate the corrosion of internal steel reinforcement. This corrosion process reduces the load-bearing capacity of concrete and affects its resistance to dynamic events, such as earthquakes or high winds.
In addition, moisture penetration and corrosive agents cause steel to expand, which aggravates existing cracks and creates new ones, further weakening the structure. If corrective action is not taken in time, cracks evolve into severe structural problems, increasing maintenance costs and reducing the life of the building.
Preventive measures
- Material design and selection: The first step to prevent cracking is to perform an adequate structural design that includes all the loads that the structure will have to withstand, both static and dynamic, and environmental factors. It is essential to select the right materials, such as steel reinforcements that meet technical specifications. The use of adequate cement and the incorporation of admixtures that control concrete shrinkage during the curing process are also necessary measures to avoid cracking.
- Proper construction practices: The correct execution of the works is necessary to prevent the formation of cracks. The concrete mix should be homogeneous and meet the strength and durability requirements established in the design. Concrete placement and compaction must be carried out correctly to eliminate trapped air and ensure good adhesion to the reinforcement. In addition, concrete curing is a critical stage that ensures complete hydration of the cement, preventing the formation of shrinkage cracks. Control of environmental conditions during curing, such as temperature and humidity, is necessary to ensure optimal results.
In conclusion, by identifying and managing the underlying causes, and with careful design and execution, it is possible to minimize the occurrence of cracks in concrete, thus ensuring the durability and safety of structures.
