23-03-2011, 02:09 PM
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.
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.