Cracks in masonry structures

Cracks are the complete or incomplete separation of concrete or masonry that breaks the masonry or concrete into two or more parts.

Cracks in masonry structures and used materials generally result from restrained movement. This movement may occur within the material, because of volume changes due to moisture acquisition or loss, temperature contraction or expansion, or result from movements of adjacent or supporting materials (deflection of beams or slabs). Also, the cracks are produced due to bad construction process and a bad
supervision; therefore it is important to carry out all code´s specifications and a good supervision from the initial stage of the construction.

There are non-structural and structural cracks, but both are a warning of something wrong in the structure.

Non-structural cracks in masonry structures

Non-structural cracks are less aggressive and do not pose a threat to the structural integrity of buildings, but may look unsightly or may create an impression of faulty work or may give a feeling of instability, also when exist penetration of moisture through then they may spoil the internal finishes thus adding to the cost of maintenance, or corrode the reinforcement, thereby adversely affecting the stability of the structure in long run. They are usually a sign of aging due to the change in moisture content, thermal and climatic conditions over time. But other factors can cause these cracks, such as creep damage, vegetation, moving foundations, settlement, and hydrostatic pressure. This non-structural crack must be monitored
and treated on time, because in the future they can become structural cracks when water seeps in and deteriorates the concrete inside, widening the cracks.

Structural cracks in masonry structures

Structural cracks are more complicated and can threaten the structural integrity of the structure. Generally, they are caused by incorrect design, buildings built on land with little admissible capacity, faulty construction or overloading, differential settlement and presence of chemicals that affect the concrete.

Cracks in the walls and partitions of masonry structures

Cracks in masonry structures generally have different shapes and characteristic, depending on the causes that produced them.

Cracks in the load-bearing

In the load-bearing walls, cracks can be:

1. Local fault is produced by defective execution or the use of parts of non- uniform quality. An appropriate selection of the pieces and following the rules of execution can avoid it.
2. Crushing of the pieces or of the mortar, this is produced by pieces with low compressive strength in the first case, and by poor mortar or thick joints in the second.
3. Buckling is produced by the exaggerated slenderness of the wall. It is manifested by crushing on the compression side and separation of the mortar pieces on the traction side. The way to avoid it is by reducing the slenderness and using adherent mortars.
4. Retraction occurs when very rich mortars or excessive fine material, great thickness of joints and low tensile strength in the pieces are used. To prevent this problem must utilize the appropriate dosage of the mortar, reducing the thickness of the joints and with effective curing of the work unit.
5. Warp occurs in walls of great length and slenderness because the transverse deformations along the wall take different directions. This problem is prevented by fixing the maximum length based on slenderness; the construction of transversal reinforcements with appropriate separation, or the fixation in its crest.
6. Flexion occurs in walls subjected to non-centred loads, due to recessed ceilings and non-centred upper walls. This problem can avoid by paying attention to the dimensioning of the section and in some cases with the construction of the belt or heel in ceilings of reinforced concrete slabs.
7. Local crush occurs when the value of the stresses originated under an isolated support exceeds the breaking stress of the parts that directly support them. This problem is prevented by providing a sufficient support surface for concentrated loads or by using more resistant materials.
8. Shear strength is produced by differential settlements in the foundation or by forces acting in areas of highly varied stresses or deformations. This problem can avoid by separating the areas subjected to very different stresses or deformations with joints, or by guaranteeing the rigidity of the construction and the uniformity of the seats.
9. Local tractions are produced by the action of concentrated loads on pillars and piers built with pieces of sufficient compression resistance, but unable to withstand the induced tensile stresses. This problem is avoided by building a distribution beam or by placing tension reinforcement under the concentrated loads.
10. Punching is produced by a force normal to the wall facing. Taking into account this problem when sizing the wall depending on the resistance of its material, it can prevent this.
11. Overturn occurs when the wall is not properly fixed at its base or at its crown and the horizontal actions (wind, earthquake, thrust) are not properly counteracted by the thickness of the wall, by transversal walls, by rigid ceilings or other constructive provisions. This problem is prevented by propping during construction, by the action of roofs or by the construction of transversal walls.
12. Tearing occurs along joint planes in walls subjected to small vertical loads and large horizontal stresses in the longitudinal direction of the wall. This problem is avoided by using highly adherent mortar and vertical stabilizing actions.

Cracks in the walls with opening

When walls have opening, cracks can be:

1. Lintel bending is produced by the excessive deformation of the lintel, which causes the formation of inclined cracks that delimit the discharge arch. This problem can avoid by building lintels of sufficient rigidity or by rigging a relief arch over the lintel.
2. Forechest flexion is produced by reaction of the foundation under the parapet or by deformation of the wall elements on both sides of the opening, due to the difference in load on the wall and on the parapet. They are inclined cracks that start from the interior corners of the wall. This problem can avoid by the prevention of these solicitations, such as greater rigidity in the foundation or of the supporting construction elements, joints between buttresses and parapets, inverted relief arches, or reinforced concrete beams in the masonry.
3. By numbness of the wooden frames occurs when the wood cannot expand when wet. It is avoided by separating the frame from the masonry at the openings or by waterproofing the wooden parts that make up the frame.
4. Due to corrosion or expansion of metal parts occurs when the frames or metal pieces that are inserted into the walls or partitions corrode due to the effect of humidity or expand without having space to expand. Protecting the metal parts or providing space for expansion can avoid this problem.
5. Non-bearing walls are masonry elements that only support their own weight, and the cracks that occur in them are due to deformation of the elements that support them, or due to the separation of other structural elements of a different nature.
6. Flattening occurs when the non-bearing wall enters load as a result of the deformation of the roof. It is preventing by giving the roof sufficient rigidity, building the enclosed walls starting with the upper floors, or leaving elastic joints in the crown courses of the wall.
7. Separation is produced by difference in deformation of the roofs between which the wall is built. It can prevent by giving greater rigidity to the structural element that supports the wall or partition, or by building a relief arch.
8. Differential settlements or deformations of resistant elements occur when differential settlements occur in the structure that supports the wall or in lateral enclosures on cantilevers, which produce a diagonal fissure. It can be avoided by reducing the differential settlements to a minimum in the first case, and in the second, by reducing the deformation of the cantilever of the structure.

Cracks in partitions

The cracks in partitions are produced by blows from the door leaves, by differential seats of structural elements adjacent to the partitions, or deformation of the ceilings or elements that support them. The appearance of the cracks depends on the deformation of the roofs due to three causes, principally: a) the upper roof deforms more than the lower one, b) the lower roof deforms more than the upper one and c) both roofs deform equally.

Cracks in parapets

The cracks in parapets are horizontal cracks, generally located between the parapet and the slab, and in the corners; and are produced by the expansion of the paving or of the concrete slab, or by the rotation of the concrete slab, or by different shrinkage of materials, for example the CMU wall and the concrete slab.

Cracks in the union of reinforced concrete columns and brick or concrete block wall are vertical cracks and are produced by the weak adherence of the mortar, the different shrinkage of master materials or the movement of the building.

Cracks in masonry walls can be repair according to type of these, for example:

• Expansive crack is of no real structural significance, although it may allow water into the cavity in masonry structures, and subsequence cause deterioration of the wall ties. Therefore, filling the crack with a mastic or sealastic compound is recommended. However, for more severe cracking it is advisable to form an expansion joint. This would be cut into the wall, filled with a compressible material with a waterproof stopper to the outside. On some modern buildings these are formed at construction stage and then hidden behind rainwater downpipes.
• The best repair in cracks above openings in masonry walls is to reset the lintel and repoint or rebuild the brickwork above, and refit the window. The poor repair is to do nothing more than repoint the cracks, as the brickwork is now resting on the new frame. However, collapse of the brickwork above the opening will be likely when the window is next replaced. But if cracks are due to inadequate bearing or loads applied above the opening, replacement of the lintel is recommended. In many cases, cracks are due to no lintels and in this one, new lintels need to be installed and the cracks repaired.

Conclusions

Depending of the type of cracks, non-structural or structural ones, it is necessary take actions to repair these and to solve the causes of these. Always it is necessary a specialist advice from a structural engineer. Our Company Eastern Engineering Group renders the services of inspection for identification of deteriorated elements and potentially unsafe conditions; and development of repairs plans, details, repair
procedures indicating products and materials.

Bibliography

–Bureau of Indian Standards (1985). Causes and Prevention of Cracks in Buildings. Department of Civil Engineering, GECA. Cracks in Masonry Structure (Causes & Prevention), 49 pages.
-Ingegeek. (2021). Tipos de Grietas. https://www.ingegeek.site/2021/06/23/tipos-de-grietas-en-edificaciones/
-Menéndez Menéndez, J. (1986). Desperfectos en construcciones de ingeniería y de arquitectura. Diagnóstico. Reparaciones. Reconstrucciones (Resumen de veinte conferencias). Editorial del Centro de Información de la Construcción.
-National Concrete Masonry Association. (2005). TEK 10-01A Crack Control in Concrete Masonry Walls.
-The Constructor. (2021). Cracks in Masonry Walls – Types, Causes and Repair of Cracks. https://theconstructor.org/building/cracks-in-masonry-walls/1464/