Shrinkage cracks in concrete

For anyone working in construction, shrinkage cracks in concrete can be a major concern. These fissures frequently show up as the concrete dries and solidifies, causing structural and aesthetic problems. To guarantee the robustness and longevity of concrete structures, it is crucial to comprehend the causes of these cracks and preventative measures.

The loss of moisture in the concrete mix is the main reason for shrinkage cracks. Concrete shrinks as the water evaporates; if this shrinkage is allowed to continue, cracks may occur. The mix design, the curing process, and the surrounding environment are some of the variables that can affect how much shrinkage occurs.

The possibility of shrinkage cracks can be reduced by using the right tools and materials. Builders can drastically lower the likelihood of these cracks arising by managing the moisture content, utilizing the proper mix proportions, and implementing efficient curing procedures. This post will discuss the reasons behind shrinkage cracks in concrete, how to prevent them, and how to fix them. It will also offer helpful tips for both pros and do-it-yourselfers.

Shrinkage cracks: acceptable values

Concrete cracks are stress concentrators and the source of harmful elements. Water seeping in and freezing over the winter causes the defect to enlarge even more, exposing the reinforcing and partially destroying the structure as a whole.

As a result, the requirements of the most recent regulatory documents, specifically SNiP 52-01-2003 "Concrete and reinforced concrete structures. Basic provisions," regulate this factor.

Concrete shrinkage crack values that are acceptable (SNiP 52-01-2003):

• No more than 0.3 millimeters with long-term opening (in accordance with the conditions of preservation of the reinforcement belt).
• No more than 0.4 millimeters with long-term opening (based on the conditions of preservation of the reinforcement belt).
• No more than 0.2 millimeters with long-term opening of cracks (for sealed structures).
• No more than 0.3 millimeters with short-term opening of cracks (for sealed structures).

Defects in concrete are prohibited in the following situations:

• Structures operating under excess pressure of liquids or gases.
• Structures and products with increased durability.
• Structures operating in conditions of increased aggressiveness of the environment.

Concrete shrinkage cracks can jeopardize a project’s structural soundness and visual appeal as the material dries out and shrinks. By comprehending the reasons behind these fractures and employing appropriate methods during the mixing, curing, and application processes, one can considerably decrease their frequency and influence, guaranteeing a more resilient and aesthetically pleasing concrete surface.

Causes of shrinkage cracks in a structure

Cracks resulting from shrinkage have three primary causes. They are all linked to transgressions of construction and concrete preparation technologies.

• Failure to comply with the proportions of the mixture components in terms of increasing the amount of sealant. An excess increase in the aggregate (water) is observed when preparing concrete manually using a sheet of metal and shovels. A larger amount of mixer significantly facilitates the mixing process, but at the same time causes rapid shrinkage and the corresponding appearance of cracking.
• Improper care of a freshly poured structure. After pouring, shrinkage cracks in concrete appear when the material dries intensively under the influence of direct sunlight. Regulatory document SNiP 3.03.01-87 “Load-bearing and enclosing structures” regulates the following actions: during the initial period of hardening, concrete is protected from precipitation and moisture loss. In practice, during the first 72 hours of setting and strengthening, covering materials should be used and the surface of the structure or product should be constantly sprayed with water.
• Shrinkage cracks can form due to a decrease in the permissible protective layer of concrete around the reinforcement. In accordance with the recommendations of the document SNiP 52-01-2003 "Concrete and reinforced concrete structures", the thickness of the protective layer of reinforcement should be no less than the diameter of the reinforcement bar, but not less than 10 mm.

Even acceptable external cracks need to be caulked and sealed. The entrance of moisture and the freezing that follows in the winter cause the crack to gradually widen, which ultimately causes the structure to gradually collapse.

Repair of shrinkage cracks

Concrete shrinkage cracks can be effectively sealed using a variety of repair compounds made of fine sand and epoxy resin. Technological stages:

• Expanding the crack using an angle grinder equipped with a "concrete" disc.
• Thorough dust removal of the damage and the adjacent area.
• Filling the crack with epoxy resin mixed with fine sand in a 1:1 ratio.

The following materials are frequently used to fix shrinkage defects: Spolchemie, ED-16, ED-20, Epoxy 520, and UZIN KR 416.

Anti-shrinkage additives are added to the concrete to stop shrinkage cracks from forming if it is not feasible or financially advantageous to maintain the concrete in compliance with SNiP 3.03.01-87 standards. KEMA NONSHRINK, Reolen AU 460 and AU 461, TM "Primeo" EC-26, Denka CSA20, and other well-known anti-shrinkage compounds are a few examples.

Concurrently, the application of anti-shrinkage additives during low-rise private building (foundation pouring, concrete wall construction, placement of blind areas, pathways, cellar ceilings, etc.) results in a notable rise in construction expenses. For instance, the price of 1 m3 of concrete solution increases by an average of 1,980 rubles when the KEMA NONSHRINK composition is used. As a result, it makes sense to prepare concrete according to precise proportions and to take good care of the poured structure when constructing a private or rural home.

Concrete shrinkage cracks are a frequent problem that can affect a structure’s longevity and aesthetic appeal. Preventing these cracks requires an understanding of the causes, which include temperature variations and water evaporation.

The likelihood of shrinkage cracks can be considerably decreased by employing appropriate curing methods, managing mix proportions, and using admixtures that minimize shrinkage. Concrete integrity can also be preserved by using best practices in construction, such as minimizing water content and making sure it dries evenly.

In order to address any cracks that do appear and stop them from getting worse over time, routine inspections and prompt maintenance are crucial. Concrete structures can be made stronger and last longer by adopting these preventive measures and exercising caution.

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