CRACKS IN BUILDING
#1

presented by:
SHABIR MALIK

[attachment=10796]
INTRODUCTION
Cracks result in when applied forces are greater than those which the building or its part can withstand. These forces may have emerged externally to the building or internally within the building or have been developed in the materials of the building as a result of Chemical changes. There may be a single force or a combination of forces having a single cause or several causes.
This is a residential building at San Francisco. Major cracks have developed on the external facade of the building. The cracks running across the entire facade of the building are diagonally directed and diagonal cracks are generally structural cracks. They occur due to structural problems in the buildings. Structural cracks could be due to major or minor problem in the structural design. Intensity of structural problem is determined on the basis of the intensity of cracks developed.
LOOPHOLES OF CRACKS
1. BUILDING BECOME UNSAFE
2. IT SPOIL THE APPERANCE OF BUILDING
3. DAMPNESS IN THE BUILDING
4. REDUCE IN MARKET VALUE
5. INCREASE IN MAINTAINENCE COST
Most cracks occur due to drying of construction water.
• These are generally superficial
• Do not affect the serviceability of the building
• Can be easily repaired
If cracks are more significant, repair work may be repeated periodically.
Structural significance of the cracks tends to be exaggerated by a natural reaction of the owner.
Many cracks do not have any effect on the stability of structure, because of “high factor of safety”.
Cracking has adverse effects on appearance. Sometimes several cracks go unnoticed for years which affect the performance of the structure.
Rain penetration through a crack depends on:
1. Construction of a building
2. Degree of exposure
3. Capillarity of fine cracks
4. Wind driven rain penetration through wide cracks
CAUSES OF CRACKS
 Structural cracks
 Due to incorrect design
 Faulty construction
 Overloading
 Non Structural cracks
 Moisture changes
 Thermal movement
 Elastic deformation
 Chemical reaction
 Foundation movement
 Settlement of soil
 Vegetation
CHANGE IN MOISTURE
Most building materials expend when they absorb moisture from atmosphere and shrink when they are dry. Cement made materials shrink due to drying up of the moisture used in their construction. The factors causing shrinkage in cement concrete and cement mortar are following.
 Excessive Water
The quantity of water used in the mortar mix can cause shrinkage. Vibrated concrete has less quantity of water and lesser shrinkage than manually compacted concrete.
 Quantity of Cement
As a general rule, the richer the mix is, the greater the shrinkage/drying will be.
 Un-graded Aggregate
Aggregate can cause shrinkage also. If un-graded and fine material/aggregate is used in cement concrete and cement mortar which requires more water and can cause greater shrinkage.
 Curing
After laying cement concrete mix, the hardening of cement takes place, causes reduction in moisture and creates shrinkage. This causes cracks in concrete work.
 Excessive Fine materials
Fine materials take more surface area and require more water for mix. The use of excessive fine materials i.e. silts; clay and dust in aggregate create more shrinkage.
 Temperature:
Concrete made in hot weather needs more water for same workability hence results in more shrinkage
Thermal Movement
All materials expand on heat and contract on cool. Thermal movement in components of structure creates cracks due to tensile of shear stresses. It is one of the most potent causes of cracking in buildings and needs attention
Elastic Deformation
When the walls are unevenly loaded, due to variation in stresses in different parts of wall the cracks are formed in walls. When two materials having wide different elastic properties are built together under the effect of load, different shear stresses in these materials create cracks at the junction. Dead and live loads cause elastic deformation in structural components of a building.
Chemical Reaction
Chemical reactions in building materials increase their volume and internal stress causes cracks. The components of structure also weaken due to chemical reactions. Some common instances of chemical reactions are following.
• Sulphate attack on cement products
• Carbonation in cement based materials
• Corrosion of reinforcement in concrete
• Alkali aggregate reaction
Certain chemical reaction in building materials result is appreciable change in volume of resulting products and internal stresses are set up which may result in outward thrust and formation of cracks.
Soluble sulphate reacts with tricalcuium aluminates in cement and hydraulic lime and form products which occupy larger volume and ends in developing cracks. An example of cracking of a floor due to coming in contact of the sub base made of brick khoa with heavy sulphate content and water can be seen in fig
Foundation Movement and Settlement of Soil
Shear cracks occur in buildings when there is large differential settlement of foundation due to any of following causes.
• Unequal bearing pressure under different parts of the structure
• Bearing pressure being in excess of safe bearing strength of the soil
• Low factor of safety in the design of foundations
• Local variation in the nature of supporting soil
Buildings on expansion clays are extremely crack prone. The soil movement in such clay is more appreciable upto a depth of 1.5 to 2M and this cause swelling and shrinkage and results in crack in the structure. The cracks due to settlement are usually diagonal in shape. Crack appearing due to swelling is vertical
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#2

presented by:
SHABIR MALIK

[attachment=10833]
INTRODUCTION
Cracks result in building when applied forces are greater than those which the building or its part can withstand.
LOOPHOLES OF CRACKS
 BUILDING BECOME UNSAFE
 IT SPOIL THE APPERANCE OF BUILDING
 DAMPNESS IN THE BUILDING
 REDUCe MARKET VALUE
 INCREASE IN MAINTAINENCE COST
CAUSES OF CRACKS
Non Structural cracks

 Moisture changes
 Thermal movement
 Elastic deformation
 Chemical reaction
 Foundation movement and settlement of soil
 Vegetation
Structural cracks
 due to incorrect design
 faulty construction
 Overloading
Moisture Changes
 Building materials expand on absorbing moisture and shrink on drying. These are generally reversible.
Shrinkage in concrete or mortar depends on a number of factors
 Cement concrete
 Water Content
 Aggregates
 Curing
 Excessive fines
 Temperature:
Thermal Movement
 All materials expand on heat and contract on cool. It is one of the most potent causes of cracking in buildings and needs attention.
ELASTIC DEFORMATION
 When two materials having wide different elastic properties are built together under the effect of load, different shear stresses in these materials create cracks at the junction
CHEMICAL REACTION
 Chemical reactions in building materials increase their volume and internal stress causes cracks. The components of structure also weaken due to chemical reactions.
 Some common instances of chemical reactions are following.
 Sulphate attack on cement products
 Carbonation in cement based materials
 Corrosion of reinforcement in concrete
 Alkali aggregate reaction
FOUNDATION MOVEMENT AND SETTLEMENT OF SOIL
 Unequal bearing pressure under different parts of the structure
 Bearing pressure being in excess of safe bearing strength of the soil
 Low factor of safety in the design of foundations
 Local variation in the nature of supporting soil
VEGETATION
 The roots of trees located in the vicinity of a wall can create cracks in walls due to growth of roots under foundation.
EARTH QUAKE
 Crack may occur due to sudden shift in lower layer of the earth. The voids in the earth might have suddenly collapsed and be filled with soil from the above. Many geological events can trigger earth movements but is continuous movement. This results in cracks.
PREVENTIONS
 Modern structures are comparatively tall and slender, have thin walls are designed for higher stresses and are built at a fast pace.
 These structures are more prone to CRACKS.
 Moreover moisture can easily reach the inside of the modern buildings due to the usage of thin walls.
 Thus measures for control of cracks in buildings assume much greater importance than ever before.
MOISTURE CHANGE
 Do not use excessive cement in the mortar mix.
 Use minimum quantity of water according to water cement ratio.
 Proper curing should be started as soon as initial setting has taken place and be continued for at least seven to ten days.
THERMAL CRACKS
 To prevent thermal cracks expansion joints, control joints and joints in case of change of shape and direction of wing in a structure are to be provided
ELASTIC DEFORMATION
 Create slip joints under the support of RCC slab on walls. Masonry work on RCC slabs and beams should not be started before drying RCC slab and beam.
 Provide horizontal movement joints between the top of brick panel and RCC beam/slab
CHEMICAL REACTION
 Use dense and good quality concrete i.e. richer mix of cement concrete 1:1.5:3 to prevent cracks.
 Avoid bricks containing too much soluble sulphates (more than 5 %) and use rich mortar in such cases.
 Use expansion and control joint at closure intervals
FOUNDATION MOVEMENT AND SETTLEMENT OF SOIL
 Prevention of moisture penetration in the surrounding areas has to be ensured by providing a waterproof blanket around the plinth.
 The masonry wall below ground level should also be separated from the adjoining soil by replacing the existing soil with coarse grain material.
 The design of foundation must be based on sound engineering principles and good practice.
Vegetation
 Do not let trees grow too close to the buildings, compound walls etc. Remove any saplings of trees as soon as possible if they start growing in or near of walls etc.
Earth Quake
 Construct the foundation of buildings on firm ground while doing construction. Tie up the building with connecting beams at foundation level, door level and roof level.
REPAIR OF CRACKS
 Cracks must be repaired immediately when observed otherwise the life of structure will reduce causing structural failure.
 They not only weaken the building but spoil the beauty of walls also.
Repair cracks giving hollow sound
 Remove plaster applying proper cut
 Prepare the surface thoroughly
 Apply fresh cement mortar and finish the surface
Repair Cracks on Joint of RCC Slab and Brickwork
 Remove plaster and old material
 Apply cut and prepare the surface
 Apply cement mortar
 Make groove
 Do curing and finishing
CONCLUSION
 Cracks must be repaired immediately when observed otherwise the life of structure will reduce causing structural failure.
 The cracks can be prevented at the time of construction
 They not only weaken the building but spoil the beauty of walls also.
 This write up tells you about repair of cracks in plaster, RCC member, Brick walls, Floor and Fine Cracks.
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