CRACKS IN CONCRETE......
WHY CRACKS DEVELOPS IN CONCRETE: A building components develops cracks whenever stress in the component exceeds its strength.
These cracks develops due to following factors: 1) Externally applied load such as dead load, live load, wind load, seismic load and due to thermal movement ,foundation settlement, moisture changes as well as due to chemical reaction.
CRACKS ARE GENERALLY CLASSIFIED AS :
1) STRUCTURAL CRACKS: Cracks which appears due to faulty design , overloading as well as due to incorrect design which causing danger of life is known as structural cracks.
2) NON STRUCTURAL CRACKS: Are develops due to internally induces stress in building material is known as non structural cracks.
CLASSIFICATION OF CRACKS BASED ON WIDTH :
THIN CRACKS : Width of cracks generally less than 1 mm.
MEDIUM CRACKS : Width of cracks generally between 1 mm to 2 mm.
WIDE CRACKS : Width of cracks more than 2 mm.
CAUSING OF NON STRUCTURAL CRACKS IN BUILDING...
1) MOISTURE MOVEMENT
2) THERMAL VARIATION
3) ELASTIC DEFORMATION
4) CREEP
5) CHEMICAL REACTION
6) FOUNDATION MOVEMENT
7) VEGETATION
HERE WE CONCENTRATE ONLY ON MOISTURE MOVEMENT ...
As we know that most of building material having pores in their structure in the form of inter molecular space due to which material expands on absorbing moisture and shrink when dry, this process is cyclic in nature (i.e reversible movement occur) which is depends upon increase and decrease in moisture and causing shrinkage in concrete.
DRY SHRINKAGE
Shrinkage is generally occurs due to loss of adsorbed water from hydrated cement paste. when concrete is initially exposed to environment their is difference between humidity of concrete and environment due to which first free water in concrete loses from large capillary pores this result is small but in small capillary pores curved menisci are formed due to loss of capillary water and the surface tension of water pull the wall of pores, thus internal negative pressure develops in the capillary pores this pressure is compressive in nature and due to which shrinkage occur in concrete.
If the concrete is continued dry than in this case volume changes occur in cement paste and causing increasing in attraction force between C-S-H hydrated products that leads to shinkage.
HOW TO MINIMISE SHRINKAGE IN CONCRETE
By using shrinkage reducing admixture.
It reduce the surface tension of water with in the pores of concrete which leads to reduction in capillary tension and pulls on the wall of the pores and reduce the magnitude of shrinkage.
By using low water cement ratio.
By increasing aggregate content in concrete.
By reducing fines content in concrete.
SOME TECHNICAL TERMS ARE GIVEN BELOW:
Capillary water : Present in voids larger than 10 nm further classified as:
free water : Removal of which is not cause shrinkage crack and other is water in small capillary pores caused shrinkage cracks.
Adsorbed water : water adsorbed on the surface of hydrated product drying of this responsible for lot of shrinkage in concrete.
Interlayer water: water held in between layer of C-S-H structure made in concrete is known as interlayer concrete.
Bound water : water held between the structure of C-S-H or calcium hydroxide or ettrigite as well as monosulphate is known as bound water.
When cement reacts with water the resultant product that forms has a lower volume about 25.4% of bound water.
Both adsorbed as well as interlayer layer water is known as gel water which is present in gel pore, size of pores is less than 10 nm.
And size of capillary pore is more than 10 nm.
WHY CRACKS DEVELOPS IN CONCRETE: A building components develops cracks whenever stress in the component exceeds its strength.
These cracks develops due to following factors: 1) Externally applied load such as dead load, live load, wind load, seismic load and due to thermal movement ,foundation settlement, moisture changes as well as due to chemical reaction.
CRACKS ARE GENERALLY CLASSIFIED AS :
1) STRUCTURAL CRACKS: Cracks which appears due to faulty design , overloading as well as due to incorrect design which causing danger of life is known as structural cracks.
2) NON STRUCTURAL CRACKS: Are develops due to internally induces stress in building material is known as non structural cracks.
CLASSIFICATION OF CRACKS BASED ON WIDTH :
THIN CRACKS : Width of cracks generally less than 1 mm.
MEDIUM CRACKS : Width of cracks generally between 1 mm to 2 mm.
WIDE CRACKS : Width of cracks more than 2 mm.
CAUSING OF NON STRUCTURAL CRACKS IN BUILDING...
1) MOISTURE MOVEMENT
2) THERMAL VARIATION
3) ELASTIC DEFORMATION
4) CREEP
5) CHEMICAL REACTION
6) FOUNDATION MOVEMENT
7) VEGETATION
HERE WE CONCENTRATE ONLY ON MOISTURE MOVEMENT ...
As we know that most of building material having pores in their structure in the form of inter molecular space due to which material expands on absorbing moisture and shrink when dry, this process is cyclic in nature (i.e reversible movement occur) which is depends upon increase and decrease in moisture and causing shrinkage in concrete.
DRY SHRINKAGE
Shrinkage is generally occurs due to loss of adsorbed water from hydrated cement paste. when concrete is initially exposed to environment their is difference between humidity of concrete and environment due to which first free water in concrete loses from large capillary pores this result is small but in small capillary pores curved menisci are formed due to loss of capillary water and the surface tension of water pull the wall of pores, thus internal negative pressure develops in the capillary pores this pressure is compressive in nature and due to which shrinkage occur in concrete.
If the concrete is continued dry than in this case volume changes occur in cement paste and causing increasing in attraction force between C-S-H hydrated products that leads to shinkage.
HOW TO MINIMISE SHRINKAGE IN CONCRETE
By using shrinkage reducing admixture.
It reduce the surface tension of water with in the pores of concrete which leads to reduction in capillary tension and pulls on the wall of the pores and reduce the magnitude of shrinkage.
By using low water cement ratio.
By increasing aggregate content in concrete.
By reducing fines content in concrete.
SOME TECHNICAL TERMS ARE GIVEN BELOW:
Capillary water : Present in voids larger than 10 nm further classified as:
free water : Removal of which is not cause shrinkage crack and other is water in small capillary pores caused shrinkage cracks.
Adsorbed water : water adsorbed on the surface of hydrated product drying of this responsible for lot of shrinkage in concrete.
Interlayer water: water held in between layer of C-S-H structure made in concrete is known as interlayer concrete.
Bound water : water held between the structure of C-S-H or calcium hydroxide or ettrigite as well as monosulphate is known as bound water.
When cement reacts with water the resultant product that forms has a lower volume about 25.4% of bound water.
Both adsorbed as well as interlayer layer water is known as gel water which is present in gel pore, size of pores is less than 10 nm.
And size of capillary pore is more than 10 nm.
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