- Cracks due to moisture change
Cracks due to moisture change can be prevented by
- Minimizing the use of rich cement mortar.
- Using lean cement mortar or composite cement-lime mortar in masonry work.
- Using stiffer and leaner concrete mix and allow adequate time for curing and drying.
- Cracks due to temperature variations
This type of cracks can be prevented by providing adequate insulation or terracing treatment over the roof slab and by introducing slip joint between the slab and the supporting walls.
Painting top of roof with reflective finish ( white wash etc.) can also serve to minimize cracks. Chances of cracking due to temperature variation can be minimized by introducing expansion, contraction, and slip joints at appropriate locations. In case of structures like, shell roof where it is difficult to provide joints, it is necessary to take the effect of thermal stresses in the structural design of roof to prevent cracks.
- Cracks due to elastic deformation and creep
Cracks in masonry occur when wall is unevenly loaded can be prevented by selecting the size and location of openings as to avoid unequal loading conditions in the same wall.
Cracks in masonry due to defections of RCC beam or slab can be prevented by designing the slab or beam in such a way that the depth provided is adequate to restrict the deflection within permissible limits.
Cracks at the junction of brick masonry with RCC columns in loading bearing walls can be prevented by ensuring adequate curing of thr RCC columns and by providing air gap between the masonry and the column. Besides this, a groove in the plaster at the joints between columns and masonry also helps in restricting crack within the groove.
The cracks in panel wall in the frame structure can be prevented by adopting following measures:
- The construction of panel wall should preferably be taken up as late as possible so that most of deformation due to shrinkage, creep etc. in R.C.C. beams and columns is allowed to take place prior to construction of panel wall.
- The panel walls should not to construct tightly between the RCC frames. Movement joints should be provided between the top of panel wall and soffit of beam. These joints may be filled up with some compressible jointing material.
- Cracks due to effect of chemical reaction
The cracks due to chemical reaction can be prevented by adopting the following measures:
- Use dense and good quality concrete and provide increased cover for R.C.C. members to prevent carbonation.
- For preventing sulphate attack, avoid use of bricks containing high percentage of suitable salts. In case the subsoil contains high proportion of sulphate salts, use rich cement mortar of concrete or sulphate resistant cement in executing the work.
- Since sulphate attack can take place only in the preence of moisture, provide adequate damp proofing treatment to ensure dry conditions.
- Cracks due to movement of ground
This type of cracks can be prevented by adopting following measures:
- In case of shrinkable soils, adopt under-reamed pile foundation.
- The structural design of the foundation should be carried out in such a manner as to achieve uniform distribution of pressure on the ground to avoid differential settlement.
- The foundation should be so proportioned that the safe bearing capacity or soil is not exceeded.
- Cracks due to vegetation
These cracks can be prevented by not planting fast growing trees near the building.
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