Cracks in-buildings-3568

CRACKS IN BUILDINGS:CRACKS IN BUILDINGS:
Some Remedial MeasuresSome Remedial Measures
Dr. J. N.JhaDr. J. N.Jha
Professor and Dean (Consultancy)Professor and Dean (Consultancy)
Department of Civil EngineeringDepartment of Civil Engineering
Guru Nanak Dev Engineering College,Guru Nanak Dev Engineering College,
LudhianaLudhiana

IS THAT CRACK SERIOUS?IS THAT CRACK SERIOUS?
• Simplest questions to ask.Simplest questions to ask.
• One of the most difficult to answer.One of the most difficult to answer.
• Prof. Mealcom Hollis-”Surveying buildings is anProf. Mealcom Hollis-”Surveying buildings is an
art, verifying the cause of failure is a science”art, verifying the cause of failure is a science”

Classification of CracksClassification of Cracks
Structural crackStructural crack Non structural crackNon structural crack
Incorrect designIncorrect design
Faulty constructionFaulty construction
OverloadingOverloading
Internal induced stress inInternal induced stress in
building materialbuilding material

Continue…Continue…
• Non Structural CrackNon Structural Crack
Penetration of moisture through crackPenetration of moisture through crack
Weathering actionWeathering action
Result in corrosion of reinforcementResult in corrosion of reinforcement
Structure become unsafe (structural crack)Structure become unsafe (structural crack)

Classification of cracksClassification of cracks
(Based on width)(Based on width)
TypeType WidthWidth
ThinThin
MediumMedium
WideWide
< 1 mm< 1 mm
1-2 mm1-2 mm
> 2 mm> 2 mm

Common sight of crackCommon sight of crack
VerticalVertical
HorizontalHorizontal
DiagonalDiagonal
StraightStraight
ToothedToothed
SteppedStepped
Map patternMap pattern
RandomRandom
UniformUniform
throughoutthroughout
Narrow at oneNarrow at one
end and graduallyend and gradually
widening at thewidening at the
otherother

Internal stress in BuildingInternal stress in Building
componentcomponent
• CompressiveCompressive
• TensileTensile
• ShearShear
• Building materialBuilding material
• 1. Masonry, Concrete, Mortar1. Masonry, Concrete, Mortar
2. Weak in tension/shear2. Weak in tension/shear
3. Causing3. Causing
tension/shear cracktension/shear crack

Present trend in constructionPresent trend in construction
• Modern StructureModern Structure
- Tall, slender, thin wallTall, slender, thin wall
- Designed for higher stressDesigned for higher stress
- Constructed at fast paceConstructed at fast pace
• More crack proneMore crack prone

Cause of cracks in buildingsCause of cracks in buildings
• Moisture changeMoisture change
• Thermal variationThermal variation
• Elastic deformationElastic deformation
• CreepCreep
• Chemical reactionChemical reaction
• Foundation movement and settlement of soilFoundation movement and settlement of soil
• VegetationVegetation

Moisture MovementMoisture Movement
• Reversible MovementReversible Movement
- Material expands on absorbing moistureMaterial expands on absorbing moisture
contentcontent
- Shrinks on dryingShrinks on drying
• Irreversible movementIrreversible movement
-- Material undergo some irreversible movementMaterial undergo some irreversible movement
due to initial moisture changedue to initial moisture change

Types and causes of cracks inTypes and causes of cracks in
ConcreteConcrete
• Before hardeningBefore hardening
DryingDrying
- Plastic shrinkagePlastic shrinkage
- Settlement shrinkageSettlement shrinkage
- BleedingBleeding
- Delayed curingDelayed curing

ConstructionalConstructional
- Formwork movementFormwork movement
- Excess vibrationExcess vibration
- Subgrade settlementSubgrade settlement
- FinishingFinishing
Early frost damageEarly frost damage

• After hardeningAfter hardening
 Unsound materialUnsound material
 Long term drying shrinkageLong term drying shrinkage
 ThermalThermal
 Moisture movementMoisture movement
 BiologicalBiological
 Structural design deficienciesStructural design deficiencies
 ChemicalChemical
 Corrosion of reinforcementCorrosion of reinforcement

Plastic shrinkage cracksPlastic shrinkage cracks
• Concrete surface loses water faster than theConcrete surface loses water faster than the
bleeding action brings it to topbleeding action brings it to top
• Quick drying of concrete at the surface results inQuick drying of concrete at the surface results in
shrinkageshrinkage
• Concrete at the plastic state can not resistConcrete at the plastic state can not resist
tensiontension
• Crack Depth 5 to 10 cm, width 3 mmCrack Depth 5 to 10 cm, width 3 mm
• Once developed difficult to rectifyOnce developed difficult to rectify

Measure to reduce plastic crackMeasure to reduce plastic crack
• Moisture the sub grade and form workMoisture the sub grade and form work
• Erect the temporary wind breakerErect the temporary wind breaker
• Erect the temporary roof to protect greenErect the temporary roof to protect green
concrete from hot sunconcrete from hot sun
• Reduce the time between placing & finishingReduce the time between placing & finishing
• In case of delay in finishing cover the concreteIn case of delay in finishing cover the concrete
with polythenewith polythene

Settlement shrinkageSettlement shrinkage
• If concrete is free to settle uniformly, no crackIf concrete is free to settle uniformly, no crack
occursoccurs
• Obstruction to uniform settlement createsObstruction to uniform settlement creates
voids/cracks (Reinforcement/Aggregate)voids/cracks (Reinforcement/Aggregate)
• Settlement crack (common in deep beam)Settlement crack (common in deep beam)

MeasureMeasure
• Pouring of concrete in layers with properPouring of concrete in layers with proper
compactioncompaction
• Revibration, if possibleRevibration, if possible

BleedingBleeding
• Upward movement of water when concrete settleUpward movement of water when concrete settle
downsdowns
• Internal bleedingInternal bleeding
- Bleeding water trapped below reinforcement &Bleeding water trapped below reinforcement &
aggregateaggregate
- Affects bonds between reinforcement and concreteAffects bonds between reinforcement and concrete
- Interface, prone to micro crackingInterface, prone to micro cracking
- Weak link in concreteWeak link in concrete
- Further loading propagate crackingFurther loading propagate cracking

• External BleedingExternal Bleeding
- Upward movement of water emerged at topUpward movement of water emerged at top
surfacesurface
- After evaporation : surface – Porous andAfter evaporation : surface – Porous and
abrasion resistance very little.abrasion resistance very little.

General ObservationsGeneral Observations
• Mason floats concrete when bleeding water stillMason floats concrete when bleeding water still
standing.standing.
• ResultsResults
-- Downward movement of coarse aggregateDownward movement of coarse aggregate
- Upward movement of fine particles (cement and water)Upward movement of fine particles (cement and water)
• Top surfaceTop surface
- Presence of fine materials develops crack and crazinessPresence of fine materials develops crack and craziness
(Craziness: occurrence of closely spaced crack at surface)(Craziness: occurrence of closely spaced crack at surface)

Delayed CuringDelayed Curing
• Common practiceCommon practice
- Delayed curingDelayed curing
- Interruption in continuous curingInterruption in continuous curing
- Curing not done for required periodCuring not done for required period
• Major cause for shrinkageMajor cause for shrinkage
• Minimum 7 to 10 days curing requiredMinimum 7 to 10 days curing required

Constructional EffectsConstructional Effects
• Crack/Deformation of plastic concrete (AfterCrack/Deformation of plastic concrete (After
Compaction)Compaction)
-Lack of rigidity of formwork (Remains unnoticed)-Lack of rigidity of formwork (Remains unnoticed)
-Use of high consistency concrete (present trend)-Use of high consistency concrete (present trend)
: Pumping requirement, Use of superplasticizer: Pumping requirement, Use of superplasticizer
-Avoid segregation by proper vibration-Avoid segregation by proper vibration
• Segregated Concrete Mix- Exhibits highSegregated Concrete Mix- Exhibits high
shrinkage crackshrinkage crack

Unsound MaterialUnsound Material
• Use of crushed sand very common nowUse of crushed sand very common now
• Amount of dust (<75 micron): Very highAmount of dust (<75 micron): Very high
• Presence of excess dust :Presence of excess dust :
- Causes crack formation- Causes crack formation
- Interfere with setting time, Shrinkage and- Interfere with setting time, Shrinkage and
BondBond
• Maximum %age of fine = 3% (Coarse aggregate)Maximum %age of fine = 3% (Coarse aggregate)

Some measures to avoid cracksSome measures to avoid cracks

Thermal expansion and shrinkageThermal expansion and shrinkage
• Assume characteristics compressive strength ofAssume characteristics compressive strength of
concrete -25 MPaconcrete -25 MPa
• Modulus of elasticity – 5000x √fck N/mmModulus of elasticity – 5000x √fck N/mm22
- 5000 x √25 = 25 x 10- 5000 x √25 = 25 x 1044
N/mmN/mm22
• Flexural strength = 0.7 x √fck = 3.5 N/mmFlexural strength = 0.7 x √fck = 3.5 N/mm22
• Coefficient of thermal expansion of concrete =Coefficient of thermal expansion of concrete =
10 x 10-10 x 10-66
/◦c/◦c
• Diurnal Variation in temperature = 20 ◦cDiurnal Variation in temperature = 20 ◦c

• Thermal shrinkage strain = 20 x 10 x 10Thermal shrinkage strain = 20 x 10 x 10-6-6
• Modulus of elasticity = Stress/StrainModulus of elasticity = Stress/Strain
• 2.5 x 102.5 x 10 44
= Stress/200x10= Stress/200x10-6-6
• Tensile Stress = 5.0 N/mmTensile Stress = 5.0 N/mm22
• Tensile Strength of concrete = 3.5 N/mmTensile Strength of concrete = 3.5 N/mm22
• Sure to cause crackSure to cause crack

Foundation settlement…Foundation settlement…

Crack due to vegetation…Crack due to vegetation…

Cracks in-buildings-3568

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