cracks in-buildings-3568

CRACKS IN CRACKS IN BUILDINGS:BUILDINGS:

Some Remedial Some Remedial MeasuresMeasures

Dr. J. N.JhaDr. J. N.JhaProfessor 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 IS THAT CRACK SERIOUS?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 Prof. Mealcom Hollis-”Surveying

buildings is an art, verifying the buildings is an art, verifying the cause of failure is a science”cause of failure is a science”

Classification of Cracks Classification of Cracks Structural crack Structural crack Non structural crack Non structural crack

Incorrect designIncorrect design

Faulty constructionFaulty construction

OverloadingOverloading

Internal induced Internal induced stress in building stress in building materialmaterial

Continue…Continue…

• Non Structural Crack Non Structural Crack Penetration of moisture through Penetration of moisture through

crackcrackWeathering actionWeathering actionResult in corrosion of reinforcementResult in corrosion of reinforcementStructure become unsafe (structural Structure become unsafe (structural

crack)crack)

Classification of cracks Classification 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

Uniform Uniform throughoutthroughout

Narrow at Narrow at one end and one end and gradually gradually widening at widening at the other the other

Internal stress in Building Internal stress in Building component component

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

Mortar Mortar

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

Present trend in Present trend in constructionconstruction

• 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 Cause of cracks in buildingsbuildings

• Moisture changeMoisture change• Thermal variationThermal variation• Elastic deformationElastic deformation• CreepCreep• Chemical reactionChemical reaction• Foundation movement and Foundation movement and

settlement of soilsettlement of soil• Vegetation Vegetation

Moisture Movement Moisture Movement

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

moisture content moisture content - Shrinks on drying Shrinks on drying • Irreversible movement Irreversible movement

-- Material undergo some irreversible Material undergo some irreversible movement due to initial moisture movement due to initial moisture change change

Types and causes of cracks Types and causes of cracks in Concretein Concrete

• Before hardeningBefore hardeningDrying Drying - Plastic shrinkagePlastic shrinkage- Settlement shrinkageSettlement shrinkage- BleedingBleeding- Delayed curingDelayed curing


ConstructionalConstructional- Formwork movementFormwork movement- Excess vibrationExcess vibration- Subgrade settlementSubgrade settlement- FinishingFinishingEarly frost damage Early 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 reinforcement Corrosion of reinforcement

Plastic shrinkage cracksPlastic shrinkage cracks

• Concrete surface loses water faster Concrete surface loses water faster than the bleeding action brings it to than the bleeding action brings it to toptop

• Quick drying of concrete at the surface Quick drying of concrete at the surface results in shrinkageresults in shrinkage

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

• 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 Measure to reduce plastic crack plastic crack

• Moisture the sub grade and form Moisture the sub grade and form workwork

• Erect the temporary wind breakerErect the temporary wind breaker• Erect the temporary roof to protect Erect the temporary roof to protect

green concrete from hot sungreen concrete from hot sun• Reduce the time between placing & Reduce the time between placing &

finishingfinishing• In case of delay in finishing cover the In case of delay in finishing cover the

concrete with polytheneconcrete with polythene

Settlement shrinkage Settlement shrinkage

• If concrete is free to settle If concrete is free to settle uniformly, no crack occursuniformly, no crack occurs

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

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

MeasureMeasure

• Pouring of concrete in layers with Pouring of concrete in layers with proper compactionproper compaction

• Revibration, if possibleRevibration, if possible

BleedingBleeding

• Upward movement of water when concrete Upward movement of water when concrete settle downssettle downs

• Internal bleedingInternal bleeding- Bleeding water trapped below reinforcement Bleeding water trapped below reinforcement

& aggregate& aggregate- Affects bonds between reinforcement and Affects bonds between reinforcement and

concrete 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 Upward movement of water

emerged at top surfaceemerged at top surface- After evaporation : surface – Porous After evaporation : surface – Porous

and abrasion resistance very little.and abrasion resistance very little.

General 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 aggregate- Upward movement of fine particles (cement and Upward movement of fine particles (cement and

water)water)• Top surface Top surface - Presence of fine materials develops crack and Presence of fine materials develops crack and

craziness craziness

(Craziness: occurrence of closely spaced crack at (Craziness: occurrence of closely spaced crack at surface) surface)

Delayed CuringDelayed Curing

• Common practice Common practice - Delayed 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 shrinkage• Minimum 7 to 10 days curing Minimum 7 to 10 days curing

required required

Constructional Effects Constructional Effects

• Crack/Deformation of plastic concrete (After Crack/Deformation of plastic concrete (After Compaction)Compaction)

-Lack of rigidity of formwork (Remains -Lack of rigidity of formwork (Remains unnoticed) unnoticed)

-Use of high consistency concrete (present -Use of high consistency concrete (present trend)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 high Segregated 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, - Interfere with setting time,

Shrinkage andShrinkage and Bond Bond

• Maximum %age of fine = 3% (Coarse Maximum %age of fine = 3% (Coarse aggregate) aggregate)

Some measures to avoid Some measures to avoid crackscracks

Thermal expansion and Thermal expansion and shrinkageshrinkage

• Assume characteristics compressive Assume characteristics compressive strength of concrete -25 MPastrength of concrete -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/mm N/mm22

• Flexural strength = 0.7 x √fck = 3.5 Flexural strength = 0.7 x √fck = 3.5 N/mmN/mm22

• Coefficient of thermal expansion of Coefficient of thermal expansion of concrete = 10 x 10-concrete = 10 x 10-66/◦c/◦c

• Diurnal Variation in temperature = 20 ◦cDiurnal Variation in temperature = 20 ◦c


• Thermal shrinkage strain = 20 x 10 x Thermal shrinkage strain = 20 x 10 x 1010-6-6

• Modulus of elasticity = Stress/StrainModulus of elasticity = Stress/Strain• 2.5 x 10 2.5 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 Tensile Strength of concrete = 3.5 N/mmN/mm22

• Sure to cause crack Sure to cause crack

Foundation settlement…Foundation settlement…

Crack due to Crack due to vegetation…vegetation…

Thanks…..Thanks…..

cracks in-buildings-3568

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