Cracks:-
Due to some faulty design, settle down of foundation, the decay of building material, and due to improper curing, a horizontal, vertical and inclined split line developed in the structure is called cracks.
Causes of cracks:-
- Faulty design
- Curing is not proper
- Settle down of foundation
- Internal stresses Developed across the section
- unsoundness of cement
- The coefficient of thermal expansion
- Rusting of iron & Decay of timber
- Permeability of moisture
- Poor Drainage system
- The growth of plants roots
Types of cracks:-
1. Surface Cracks
2. Deep cracks
3. Horizontal cracks
4. Vertical
5. Diagonal
6. Straight & Branching cracks
Reasons for cracks and their prevention
1.1 Horizontal cracks in masonry and plaster at floor and roof slab level:-
Every building material like wood, Steel,
cement, glass etc. are made up of different temperature and expand or contract as per their properties we also called is coefficient of thermal expansion. The coefficient of thermal expansion of concrete and steel match among themselves so we are used concrete and steel together in the slab, column, beam etc. so where in the structure concrete meet or touch with other material it is very important to give attention otherwise a long horizontal, vertical and inclined cracks across it.
cement, glass etc. are made up of different temperature and expand or contract as per their properties we also called is coefficient of thermal expansion. The coefficient of thermal expansion of concrete and steel match among themselves so we are used concrete and steel together in the slab, column, beam etc. so where in the structure concrete meet or touch with other material it is very important to give attention otherwise a long horizontal, vertical and inclined cracks across it.
Prevention:-
By using chicken wire mesh at the joint of the beam with wall or column- wall and electric or plumbing fitting. By using groove along the joint of beam and column or joint of ceiling and wall edge.
Foundation: –
The first aim of the foundation is to distribute the load of the superstructure over a large area or to transmit the load to the hard base of soil but due to an earthquake, melting of glaciers, improper drainage system, soil and old tree root growth foundation goes settle down and crack developed.
Precaution during construction of Foundation:-
- Design the house as per Indian standard code of earthquake
- Improve drainage system
- Check the property of soil because clay soil undergoes excessive volume change of being highly plastic and if a structure is constructed on a sandy soil use deep foundation
- Check the Position of water-table
- The depth of foundation should be more than the underground defects which may be in the form of faults, caves, and mines on manmade like sewer pipes, electric,water-supply lines etc.
1.3 Sources of Cracks develop due to door and window:-
1. When the door & window comes in the contact of moisture or dampness then they are difficult to close due to which we close it strongly that’s why the joint of brick masonry open and Because of the storm and Hurricanes also door and window close very fast and development of crackers occurs
Prevention:-
1. Use door closer
2. Apply paint on timber because the paint is indispensable for the proper maintenance and preservation of wooden structure against wrapping, checking, or decay. Most of the metal corrode if not painted at suitable intervals. Painting enables the masonry and concrete work to resist checking and disintegration, thereby extending the life of the structure.
1.4 Cracks at the junction of New building with old
when a new Building is a tooth with old building there is a likelihood of cracks offering at the junction because of different settlement like expansion, contraction.
Prevention:-
expansion joint should be provided between the new and old building and fill it properly with insulation board and cover with sealant and expansion joint tape.
1.5 Hairline crack:-
The property of cement plaster is that he shrinks and due to shrinkage of plaster hairlines cracks are visible and also due to chemical reactions at the surface of the plaster
Prevention:-
By using SBR product in concrete or plastering because SBR product increase the flexibility of cement plaster and concrete, reduce the chances of cracks
2. Proper curing must be required
3:- Use wooden float in place iron float.
1.6 Cracks in beam:-
The bending movement is maximum at the mid-span of simply supported beam and shear force is max. at the support
1. when the B.M is max.in the mid-span and shear force is zero. The stress tries to develop the vertical cracks
2. due to Diagonal tension cracks are inclined at 45 due to shear only
3. In between the support and mid-span cracks are inclined at 45 to 90 degree due to the combined effect of shear force and bending moment
To avoid such cracks, shear reinforcement provided :-
In the form of vertical bars known as stirrups
In the form of bent Up Bar inclined an angle at a right angle to the plane of diagonal tension
In the form of the combination of stress and incline bar or by using best Grade of concrete
Percentage of steel reinforcement.
Repairs of cracks:-
Grouting operation:-
In case of the concrete structure when a grout is forced due to pressure into an opening in concrete and masonry structure to fill the cavities is called grouting
- V- groove should be made along the length of joints, Cracks and weak portion
- GI- nipple should be fixed at the suitable area and pressure grouting should be done using approved grout
- The Groove should be filled with SBR mortar
- The Groove should be saturated with water before grouting
- In case of vertical grouting should start from downside to upper side
Gunting operation:-
Throwing mixed concrete with force on the cracks with the help of concrete pumps and a concrete gun. This method is common in large concrete works. In tunnels, the cracks in the rocks are repaired with this method.
Cracks fillers:-
by using high-quality polymer, graded filler & additives materials we can fill internal & external surface cracks in plaster. The fillers should not be used more than 5 to 8 mm thick cracks so when the width of the cracks is more than 10 mm then widening the cracks and undercutting the edges in dovetailed fashion and apply epoxy bonding agent or repaired by forcing down mortar consisting of plaster of Paris, cement and sand mortar.
THANK YOU
This is a complete guide about cracks….very good.
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You should make a blog on Steel, About good steel, % of steel in slab, column, according to IS Code 456-2000.
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