What Is Crack?
A crack is a crack in which concrete is completely or incompletely separated into two or more parts due to destruction or destruction. Concrete cracks are an inherent characteristic that cannot be completely prevented, but can only be controlled and minimized. Concrete is a material with very low tensile strength. If the tensile stress in the structure exceeds the ultimate strength of the concrete, it is easy to crack.
What Are The Type Of Cracks?
Crack may be divided in two categories:
Structural Crack: There are many reasons for structural cracks, such as Improper construction, overloading of structural elements, overloading of the land where the building is located, or other similar factors. Extensive cracks in foundation walls, beams, columns or slabs, etc.
Non-Structural Cracks: Non-structural cracks are usually caused by forces in the building. These forces are caused by changes in the size of the components, fluctuations in humidity, fluctuations in temperature, and the influence of gases, liquids and solids on the components.
How We Should Investigate Cracks?
The following information helps in diagnosing the cracks:
- Whether the crack is old or new.
- Pattern of the cracks.
- Whether it appears on the opposite face of the member also.
- Soil condition, type of foundation used, and movement of ground if any.
- Study of specification, method of construction, used and the test result at the site if any.
- Observations on the similar structures in the same locality.
- Climatic condition during which the structure has been constructed.
What Should Be The Limitation Of Crack Width?
According to IS456:2000 Depending on the exposure conditions limitations on crack width are imposed as follows:
- For members in water storage units, sewage treatment plants, structures in chemically hazardous atmosphere, etc. Cracks are not permitted in R.C. members.
- In severe atmosphere up to 0.1mm crack width is permitted.
- Moderate atmosphere up to 0.2mm crack width is permitted.
- In mild atmosphere the surface width of cracks should not, in general exceed 0.3mm in members where cracking does not have any serious adverse effects upon the preservation of reinforcing steel nor upon the durability of structure.
What Could Be Causes For The Occurrence Of Cracks?
- structural deficiency resulting from design deficiency or construction deficiency and overloading.
- Settlement of ground.
- Temperature and Shrinkage effects.
- Cracks due to faulty workmanship and poor construction practice.
Cracks, Their Causes And Preventive Measures
Crack due to Structural deficiencies and overloads
Causes:
- Cracks occur due to shear, flexural and torsional steel deficiency.
- Cracks occur due to abrupt curtailment of reinforcing bars, construction joints etc.
- Cracks due to overloading of members.
- Improper anchorage.
Preventive Measures:
- Special attention should be paid to the design and details of the structure. In these structures, cracks may cause serious maintainability problems. In addition to careful planning and refinement, these structures also require continuous monitoring during all construction phases.
- Only when the designer provides information about the structural load limits and the constructor takes these limits into account, can damage caused by accidental overloading of the structure be prevented.
- Ensure proper anchorage to the reinforcing bars.
- Follow proper design specifications.
Crack due to Shrinkage and Temperature Effect
Causes:
- The common cause of shrinkage cracks in concrete walls is excessive moisture in the concrete. Generally, a higher water content in a concrete mixture will result in greater shrinkage. This can be clearly seen on some concrete walls with excessive cracks.
- A typical case of cracks caused by temperature changes is a roof panel, which is exposed to sunlight and alternately expands and contracts. This movement of the slab pushes out the top layer of the masonry and causes horizontal cracks. On the load-bearing wall.
Preventive measures:
- Adequate insulating or terracing treatment over roof slab and by introducing joint between the slab and the supporting wall.
- Chances of cracking due to temperature variation can be minimized by introducing expansion, contraction joints at appropriate locations.
- Painting top of roof with reflective finish such as white wash can also minimize cracks.
Crack due to Settlement
Causes:
- Soil consolidation under the footings.
- Soil swelling due to inadequate or blocked surface or house drainage.
- Soil heaving due to frost or excessive root growth.
- Changes in water table level.
- Gradual downward drift of clay soils on slopes.
- Soil compaction or movement due to vibration from heavy equipment, vehicular traffic, or blasting, or from ground tremors (earthquakes).
Preventive Measures:
- The structural planning of the foundation should be carried out in a way to ensure the uniform distribution of pressure on the ground to avoid different settlements.
- In case of shrinkable soils, adopt under reamed pile foundation.
- The foundation should be so proportioned that the safe bearing capacity of soil is not exceeded.
- The soil should be well compacted.
Cause due to Faulty Workmanship and Poor Construction
Causes:
- Improper bar detailing.
- Improper reinforcing steel placement.
- Premature removal of forms.
- Improper column form placement.
- Cold joints, segregation.
- Plastic shrinkage cracking.
Preventive Measures:
- By providing proper water cement ratio.
- Proper support for forms.
- Proper curing.
- Following proper design codes and recommendations.
