Cracks, which could be classified according to their thickness as fissures or fractures, are serious problems in the construction industry that can negatively affect aesthetics, durability and, most importantly, the structural characteristics of a project. They can happen anywhere, but occur especially in walls, beams, columns, and slabs, and usually, are caused by strains not considered in the design.
Fractures are usually of lesser severity. In general, they appear more on the surface of the structure. They are narrow and elongated, with openings less than 0.5mm. Sometimes they are not even visible to the naked eye. Generally, they do not imply structural problems but can lead to more serious consequences. It is important to note if the fracture grows over time or remains stable, because it may be the first stage of a fissure.
If not looked after, the next stage or a fracture could lead to deeper openings of 0.5 to 1.5mm. They can be seen without difficulty and are much more dangerous than the fractures because the rupture of the structural element has already occurred and can affect the safety of the part.
Fissures are slits with openings greater than 1.5mm, deep and well highlighted. With this magnitude, it allows air and water to penetrate the interior of the part, which requires immediate attention. They may cause corrosion of the armature or undesired chemical reactions in the material. One should not simply close them without researching the causes and provide the solution to the problem that caused it.
The main reasons that may be related to the occurrence of these cracks are the following:
- Unplanned structural impairment: due to poorly designed calculations and inadequately overload predictions;
- Unforeseen accommodation of constructive elements: Whenever a building is built, there is a settlement of the ground, a settlement to a greater or lesser degree. Thus, depending on how the foundation was made, one part of the construction can yield more than the other and with that displacement, it could cause cracks, known in the technical area as differential repression;
- Early removal of shoring elements: during the construction phase it is necessary to wait for the structural parts to acquire a minimum resistance before the shoring is removed. For example, slabs and beams should remain supported for at least 28 days;
- Thermal expansion: some parts of the building are more or less exposed to the sun during periods of the day, thus dilate or retract more than others, which can cause cracks, such as a slab that dilates with the sun causing the cracks;
- Material retraction: it is the loss of water by chemical reactions or evaporation in the coating layers and in concrete pieces such as slabs, pillars, and beams. For example, paint in the drying period, grout mortar, slab upon receiving too much sun and chemical reactions of the cement, these occur when there is the loss of moisture and thus the parts retract, their size is reduced and can arise cracks;
- Infiltration: when there is a leak or poor waterproofing of the slab or reservoirs of water enter the part, in the case of concrete the water will penetrate and will gradually reach the iron armature causing oxidation and, consequently, increasing the diameter of the bars, which will result in the pressure of the concrete and hence the beginning of the cracks. The consequence of this will be the fall of parts of the concrete, leaving the ironwork exposed, accelerating the process of corrosion;
- Vibrations and tremors: poorly designed foundations along with excess traffic on the street, elevators, nearby buildings, and subway are some reasons for continuous vibration to cause cracks;
- Defects in the formulation of the product and errors in the application: The concrete traces, represented by the proportion of the different materials that compose it, must be very well dimensioned, as it is fundamental to obtain the resistance to withstand the expected loads. A mortar with a lot of or little water, or being used after its period of handle, can cause numerous cracks in the coating of a wall.
See below some of the causes for cracking:
Cracks on beam due to insufficient positive reinforcement
Probable causes:
- Insufficiency of longitudinal reinforcement;
- Insufficient anchorage of positive reinforcement;
- Overloads than predicted in structural calculation.
Cracks on beam due to insufficient negative reinforcement
Probable causes:
- Insufficiency of longitudinal reinforcement (negative);
- Insufficient anchorage of negative reinforcement;
- Overloads than predicted in the strucutral calculation.
Cracks on beam due to shear
Probable causes:
- Insufficiency of transverse reinforcement (stirrups);
- Low resistance concrete;
- Overloads than predicted in the structural calculation;
- Misaligned stirrups.
Cracks on beam due to retraction of concrete
Probable causes:
- Premature concrete drying (improper curing causing water evaporation);
- Thermal contraction due to differences in temperature;
- Inadequate water-cement connection;
- Inadequate densification or badly vibrated concrete.
Cracks on the pillar due to repression at the foundation
Probable causes:
- Foundations stress;
- Load higher than expected;
- Inadequate resistance concrete.
Cracks on the pillar due to insufficiency of stirrups
Probable causes:
- Stirrups insufficiency;
- Overload of the longitudinal reinforcement;
- Buckling of the longitudinal reinforcement.
Cracks on slabs due to insufficient positive reinforcement
Probable causes:
- Insufficiency of positive reinforcement;
- Overload than predicted in structural calculation;
- Insufficient anchorage of the reinforcement.
Cracks on slabs due to excessive overload
Probable causes:
- Insufficient concrete thickness;
- Overload than predicted in structural calculation.
Cracks on the corner of windows and doors
Probable causes:
- Unplanned overloads;
- Nonexistent or poorly executed lintel and sill.
Cracks on masonry of facades
Probable causes:
- Premature connection of masonry
- Deficiency of the connection method;
- Bending deformations of slabs and beams that support the walls.
Inclined cracks in facades
Probable causes:
- Shear stress
It can be said that when observing the appearance of cracks in structural elements such as pillars, beams or slabs or even in walls, it is necessary to communicate the problem to the calculating engineer or, if it is not possible, to call another qualified professional, in order to establish an accurate diagnosis and to determine the alternatives for correcting the defect in order to provide the necessary repairs.
Originally published on 27 September, 2017
