cracks in buildings

CRACKS IN BUILDINGS:CRACKS IN BUILDINGS:CRACKS IN BUILDINGS:CRACKS IN BUILDINGS:Some Remedial MeasuresSome Remedial Measures

Dr. J. N.JhaDr. J. N.JhaJ JJ JProfessor and Dean (Consultancy)Professor and Dean (Consultancy)Department of Civil EngineeringDepartment of Civil Engineering

Guru Nanak Dev Engineering College,Guru Nanak Dev Engineering College,Ludhiana Ludhiana

IS THAT CRACK SERIOUS?IS THAT CRACK SERIOUS?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.One of the most difficult to answer.One of the most difficult to answer.•• Prof. Mealcom HollisProf. Mealcom Hollis--”Surveying buildings is an ”Surveying buildings is an

if i h f f il i i ”if i h f f il i i ”art, verifying the cause of failure is a science”art, verifying the cause of failure is a science”

Classification of CracksClassification of CracksClassification of Cracks Classification of Cracks

Structural crackStructural crack Non structural crackNon structural crackStructural crack Structural crack Non structural crack Non structural crack

Incorrect designIncorrect design Internal induced stress inInternal induced stress inIncorrect designIncorrect designFaulty constructionFaulty constructionO l diO l di

Internal induced stress in Internal induced stress in building materialbuilding material

OverloadingOverloading

ContinueContinueContinue…Continue…

•• Non Structural Crack Non Structural Crack Penetration of moisture through crackPenetration of moisture through crackPenetration of moisture through crackPenetration of moisture through crackWeathering actionWeathering actionResult in corrosion of reinforcementResult in corrosion of reinforcementStructure become unsafe (structural crack)Structure become unsafe (structural crack)Structure become unsafe (structural crack)Structure become unsafe (structural crack)

Classification of cracks Classification of cracks (Based on width)(Based on width)

TypeType WidthWidth

ThinThin < 1 mm< 1 mmThinThinMediumMediumWidWid

1 mm 1 mm11--2 mm2 mm> 2> 2WideWide > 2 mm> 2 mm

Common sight of crackCommon sight of crackCommon sight of crackCommon sight of crack

VerticalVerticalHorizontalHorizontal

StraightStraightToothedToothed

Uniform Uniform throughoutthroughout

DiagonalDiagonal SteppedSteppedMap patternMap pattern

Narrow at one Narrow at one end and gradually end and gradually Map patternMap pattern

RandomRandom

ggwidening at the widening at the other other

Internal stress in Building Internal stress in Building component component

•• Compressive Compressive •• TensileTensile•• ShearShear•• Building materialBuilding material•• Building materialBuilding material•• 1. Masonry, Concrete, Mortar 1. Masonry, Concrete, Mortar

2. Weak in tension/shear 2. Weak in tension/shear 3. Causing tension/shear crack 3. Causing tension/shear crack

Present trend in constructionPresent trend in constructionPresent trend in constructionPresent trend in construction

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

Cause of cracks in buildingsCause of cracks in buildingsCause of cracks in buildingsCause of cracks in buildings

•• Moisture changeMoisture change•• Thermal variationThermal variationThermal variationThermal variation•• Elastic deformationElastic deformation•• CreepCreep•• Chemical reactionChemical reactionChemical reactionChemical reaction•• Foundation movement and settlement of soilFoundation movement and settlement of soil•• Vegetation Vegetation

Moisture MovementMoisture MovementMoisture Movement Moisture Movement

•• Reversible Movement Reversible Movement -- Material expands on absorbing moistureMaterial expands on absorbing moistureMaterial expands on absorbing moisture Material expands on absorbing moisture

content content Sh i k d iSh i k d i-- Shrinks on drying Shrinks on drying

•• Irreversible movement Irreversible movement -- Material undergo some irreversible movement Material undergo some irreversible movement

d t i iti l i t hd t i iti l i t hdue to initial moisture change due to initial moisture change

Types and causes of cracks in Types and causes of cracks in ConcreteConcrete

•• Before hardeningBefore hardeningDryingDryingDrying Drying

-- Plastic shrinkagePlastic shrinkage-- Settlement shrinkageSettlement shrinkage-- BleedingBleeding-- BleedingBleeding-- Delayed curingDelayed curing


ConstructionalConstructional-- Formwork movementFormwork movementFormwork movementFormwork movement-- Excess vibrationExcess vibration-- Subgrade settlementSubgrade settlement-- FinishingFinishing-- FinishingFinishing

Early frost damage Early frost damage


Af h d iAf h d i•• After hardeningAfter hardeningUnsound materialUnsound materialLong term drying shrinkageLong term drying shrinkageThermalThermalMoisture movementMoisture movementBiologicalBiologicalo og cao og caStructural design deficienciesStructural design deficienciesChemicalChemicalChemicalChemicalCorrosion of reinforcement Corrosion of reinforcement

Plastic shrinkage cracksPlastic shrinkage cracksPlastic shrinkage cracksPlastic shrinkage cracks

•• Concrete surface loses water faster than the Concrete surface loses water faster than the bleeding action brings it to topbleeding action brings it to topg g pg g p

•• Quick drying of concrete at the surface results in Quick drying of concrete at the surface results in shrinkageshrinkageshrinkageshrinkage

•• Concrete at the plastic state can not resist Concrete at the plastic state can not resist tension tension

•• Crack Depth 5 to 10 cm width 3 mmCrack Depth 5 to 10 cm width 3 mm•• 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 crackMeasure to reduce plastic crack Measure 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 breakerErect the temporary wind breakerErect the temporary wind breaker•• Erect the temporary roof to protect green Erect the temporary roof to protect green

f hf hconcrete from hot sunconcrete from hot sun•• Reduce the time between placing & finishingReduce the time between placing & finishingp g gp g g•• In case of delay in finishing cover the concrete In case of delay in finishing cover the concrete

ith l thith l thwith polythenewith polythene

Settlement shrinkageSettlement shrinkageSettlement shrinkage Settlement shrinkage

•• If concrete is free to settle uniformly, no crack If concrete is free to settle uniformly, no crack occursoccurs

•• Obstruction to uniform settlement creates Obstruction to uniform settlement creates voids/cracks (Reinforcement/Aggregate)voids/cracks (Reinforcement/Aggregate)voids/cracks (Reinforcement/Aggregate)voids/cracks (Reinforcement/Aggregate)

•• Settlement crack (common in deep beam) Settlement crack (common in deep beam)

MeasureMeasureMeasureMeasure

•• Pouring of concrete in layers with proper Pouring of concrete in layers with proper compactioncompactionpp

•• Revibration, if possibleRevibration, if possible

BleedingBleedingBleedingBleeding

•• Upward movement of water when concrete settle Upward movement of water when concrete settle downsdowns

•• Internal bleedingInternal bleeding-- Bleeding water trapped below reinforcement & Bleeding water trapped below reinforcement & eed g wa e apped be ow e o ce e &eed g wa e apped be ow e o ce e &

aggregateaggregateAffects bonds between reinforcement and concreteAffects bonds between reinforcement and concrete-- Affects bonds between reinforcement and concrete Affects bonds between reinforcement and concrete

-- Interface, prone to micro crackingInterface, prone to micro cracking-- Weak link in concreteWeak link in concrete-- Further loading propagate cracking Further loading propagate cracking


•• External BleedingExternal Bleeding-- Upward movement of water emerged at topUpward movement of water emerged at topUpward movement of water emerged at top Upward movement of water emerged at top

surfacesurfaceAf i fAf i f P dP d-- After evaporation : surface After evaporation : surface –– Porous and Porous and abrasion resistance very little.abrasion resistance very little.

General ObservationsGeneral ObservationsGeneral Observations General Observations

•• Mason floats concrete when bleeding water still Mason floats concrete when bleeding water still standing.standing.

•• Results Results -- Downward movement of coarse aggregateDownward movement of coarse aggregateow wa d ove e o coa se agg ega eow wa d ove e o coa se agg ega e-- Upward movement of fine particles (cement and water)Upward movement of fine particles (cement and water)

T fT f•• Top surface Top surface -- Presence of fine materials develops crack and craziness Presence 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 CuringDelayed CuringDelayed Curing

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

Constructional EffectsConstructional EffectsConstructional Effects Constructional Effects

•• Crack/Deformation of plastic concrete (After Crack/Deformation of plastic concrete (After Compaction)Compaction)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: Pumping requirement, Use of superplasticizer: Pumping requirement, Use of superplasticizer--Avoid segregation by proper vibrationAvoid segregation by proper vibration•• Segregated Concrete MixSegregated Concrete Mix-- Exhibits high Exhibits high

shrinkage crackshrinkage cracksh age c acsh age c ac

Unsound MaterialUnsound MaterialUnsound MaterialUnsound Material

f h d df h d d•• 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( ) y g( ) y g•• Presence of excess dust :Presence of excess dust :

Ca ses crack formationCa ses crack formation-- Causes crack formationCauses crack formation-- Interfere with setting time, Shrinkage andInterfere with setting time, Shrinkage and

Bond Bond •• Maximum %age of fine = 3% (CoarseMaximum %age of fine = 3% (CoarseMaximum %age of fine 3% (Coarse Maximum %age of fine 3% (Coarse

aggregate) aggregate)

Some measures to avoid cracksSome measures to avoid cracksSome measures to avoid cracksSome measures to avoid cracks

Thermal expansion and shrinkageThermal expansion and shrinkage

•• Assume characteristics compressive strength of Assume characteristics compressive strength of concrete concrete --25 MPa25 MPa

•• Modulus of elasticity Modulus of elasticity –– 5000x √fck N/mm5000x √fck N/mm22

5000 √25 25 105000 √25 25 1044 N/N/ 22-- 5000 x √25 = 25 x 105000 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/mm22g /g /•• Coefficient of thermal expansion of concrete = Coefficient of thermal expansion of concrete =

10 1010 10 66//10 x 1010 x 10--66//◦◦cc•• Diurnal Variation in temperature = 20 Diurnal Variation in temperature = 20 ◦◦ccpp


•• Thermal shrinkage strain = 20 x 10 x 10Thermal shrinkage strain = 20 x 10 x 10--66

•• Modulus of elasticity = Stress/StrainModulus of elasticity = Stress/StrainModulus of elasticity Stress/StrainModulus of elasticity Stress/Strain•• 2.5 x 10 2.5 x 10 44 = Stress/200x10= Stress/200x10--66

•• 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/mm22Tensile Strength of concrete = 3.5 N/mmTensile Strength of concrete = 3.5 N/mm•• Sure to cause crack Sure to cause crack

Foundation settlementFoundation settlementFoundation settlement…Foundation settlement…

Crack due to vegetationCrack due to vegetationCrack due to vegetation…Crack due to vegetation…

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cracks in buildings

Documents

shrinkage concrete

plastic crack moisture

concrete mix

concrete interface

spaced crack

crack serious

green concrete f

g g p quick drying of