What are the Different Types of Concrete Cracks and How to Fix Them?

What are the Different Types of Concrete Cracks and How to Fix Them?

Cracks can form in a concrete structure in a variety of ways. These can be superficial or critical to the structure's integrity, and they can have a variety of causes and, as a result, a variety of solutions. The issue can be analyzed, and repair procedures implemented based on the type of cracks. Striking the broken concrete with a hammer is a straightforward way to determine if the cracks are superficial or deep. If the hammer makes a ringing noise, the cracks are superficial; if the noise is dull, the concrete has delaminated, and the crack is deep.

Determining permissible crack width and when cracks become problematic is a subjective question with no clear cut and precise answer. However, the following criteria might be used as a guideline for cracks that emerge in a structure after a lengthy period of service.

Cracks that are less than 1/16 inch wide and do not penetrate deep into the concrete can be completely ignored because they're normal superficial cracks.

Cracks ranging in width from 1/16 inch to 1/4 inch must be evaluated. These can also be ignored if they are shallow and static, i.e., do not lengthen or broaden over time.

If cracks are wider than 1/4 inch, they must be thoroughly analyzed by a structural engineer, and corrective procedures must be implemented in accordance with structural requirements.

Non-Structural Cracks:

If the cracks are very thin hairline fractures, it may not be a problem because RCC will crack to pass the load to the steel reinforcement, which is normal RCC behavior. These cracks are tight and barely visible, and they do not threaten the structural integrity of the members. These cracks do not need to be treated unless they begin to move or widen. Cracks that are tight and do not allow water to penetrate but are not deep enough to extend to the section's entire depth normally do not require treatment. However, if necessary, they can be remedied by using crack filler, which seals the cracks and prevents moisture from entering.

Shrinkage Cracks

Shrinkage Cracks:

Concrete shrinkage can be classified into two types: drying shrinkage and plastic shrinkage. Drying Shrinkage fractures are caused by the loss of capillary water in concrete, which occurs when concrete is not adequately cured and dries up prematurely. Tensile strains in concrete generate cracks as it dries and shrinks. Type-K can be used to control concrete shrinkage (Non-Shrinkage cement). Drying shrinkage cracks are usually not structurally significant. They can be treated by fixing the cracks and injecting epoxy into them to seal them.

Plastic shrinkage cracks, on the other hand, can penetrate to the full depth of the concrete structure. They are caused by rapid water loss from fresh concrete or by aggregate settlement in the concrete. These cracks are more common in slabs with a wide surface area where water can quickly evaporate. Water escaping from the surface can be avoided by covering the concrete with a PE sheet or by wet curing the concrete.

Structural Cracks

Structural Cracks:

If cracks continue to widen in length and width, it is a sign that something is wrong. It indicates that the member is highly stressed. The placement of cracks indicates the breakdown mode of the structural part. In beams, for example, there are primarily two types of fractures: shear cracks or flexural cracks, as illustrated in the image below.

If a beam develops these kinds of cracks, it may need to be retrofitted with jacketing or the load may need to be lowered in order to keep the stress within acceptable bounds. While flexural failure of a beam should be ductile if the beam is properly built, shear failure of a beam can be brittle and sudden.

Compression failure cracks in the beam may appear if the beam was not designed properly. This kind of failure will occur if the beam is over-reinforced. Concrete will crush along with the appearance of cracks in the compression zone of the beam.

Such cracks can be fixed by jacketing the beam and adding more compression reinforcement so that a balanced design is attained.

Another kind of structural cracking that results from the rusting of reinforcement is also possible. These can be found horizontally and on the sides, bottom, top, or underside of a beam or slab. They will be as deep as the concrete cover. If so, the concrete cover must be taken off, the rust must be removed from the reinforcement all around it, and the member must then be restored by applying epoxy coating or cement based repair material or rust inhibitor and polymer.

Alkali-Silica Reaction may be the cause of another sort of cracking (ASR). This occurs when concrete's alkalies react with certain of the minerals found in aggregates. If using reactive aggregates is necessary and cannot be avoided, aggregates should be evaluated for ASR or low alkali cement should be used. These resemble alligator cracks and have white reaction byproducts visible within them, as illustrated below:

Alligator Cracks

These are the most challenging cracks to deal with. The alkali-silica reaction will continue as long as alkali and reactive silica are present in cement and in touch with each other. The reaction will come to a halt if any of these requirements are no longer met. Although there may be few cracks in the structure at first, the potential for ASR to persist is high, which means that cracking will continue and eventually grow large. As a result, depending on the extent of the damage and the likelihood of ASR continuing, repair work can be carried out by removing the damaged concrete and jacketing the member. In the worst-case scenario, structural members may need to be dismantled and rebuilt.