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Cracks in-buildings-3568
Cracks in buildings can be either structural or non-structural. Structural cracks indicate failure or overloading of the building, while non-structural cracks do not compromise safety but can allow water penetration. Cracks are classified based on their width as thin, medium, or wide. Their appearance can take different forms like vertical, horizontal, diagonal, or irregular patterns. Cracks have various causes including moisture changes, thermal effects, material issues, foundation movement, or vegetation. The document provides details on specific crack types like plastic shrinkage cracks, settlement cracks, bleeding cracks, and those due to delayed curing or constructional defects. It also discusses cracks in concrete in more depth and suggests measures to prevent or minimize cracking in
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Cracks in-buildings-3568
- 1. CRACKS IN BUILDINGS:CRACKSIN 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
- 2. IS THAT CRACKSERIOUS?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”
- 3. Classification of CracksClassificationof 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
- 4. Continue…Continue… • Non StructuralCrackNon 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)
- 5. Classification of cracksClassificationof 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
- 6. Common sight ofcrackCommon 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
- 7. Internal stress inBuildingInternal 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
- 8. Present trend inconstructionPresent 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
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- 13. Cause of cracksin 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
- 14. 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
- 15. Types and causesof cracks inTypes and causes of cracks in ConcreteConcrete • Before hardeningBefore hardening DryingDrying - Plastic shrinkagePlastic shrinkage - Settlement shrinkageSettlement shrinkage - BleedingBleeding - Delayed curingDelayed curing
- 16. Continue…Continue… ConstructionalConstructional - Formwork movementFormworkmovement - Excess vibrationExcess vibration - Subgrade settlementSubgrade settlement - FinishingFinishing Early frost damageEarly frost damage
- 17. Continue…Continue… • After hardeningAfterhardening 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
- 18. Plastic shrinkage cracksPlasticshrinkage 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
- 19. Measure to reduceplastic 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
- 20. 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)
- 21. MeasureMeasure • Pouring ofconcrete in layers with properPouring of concrete in layers with proper compactioncompaction • Revibration, if possibleRevibration, if possible
- 22. BleedingBleeding • Upward movementof 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
- 23. Continue…Continue… • External BleedingExternalBleeding - 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.
- 24. 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)
- 25. 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
- 26. 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
- 27. 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)
- 28. Some measures toavoid cracksSome measures to avoid cracks
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- 40. Thermal expansion andshrinkageThermal 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
- 41. Continue…Continue… • Thermal shrinkagestrain = 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
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- 49. Crack due tovegetation…Crack due to vegetation…
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