IS THAT CRACK SERIOUS Simplest questions to ask

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

Cracks: --these are the defects in the construction. • • • Due to movement of ground. Temperature variation Moisture changes Chemical reaction Creep & elastic deformation Vegetation.

Classification of Cracks Structural crack Non structural crack Incorrect design Faulty construction Overloading Internal induced stress in building material

e… • Non Structural Crack v. Penetration of moisture through crack v. Weathering action v. Result in corrosion of reinforcement v. Structure become unsafe (structural crack)

Classification of cracks (Based on width) Type Width Thin Medium Wide < 1 mm 1 -2 mm > 2 mm

Common sight of crack Vertical Horizontal Diagonal Straight Toothed Stepped Map pattern Random Uniform throughout Narrow at one end and gradually widening at the other

Internal stress in Building component • • • Compressive Tensile Shear Building material 1. Masonry, Concrete, Mortar 2. Weak in tension/shear 3. Causing tension/shear crack

Present trend in construction • • Modern Structure Tall, slender, thin wall Designed for higher stress Constructed at fast pace More crack prone

Cause of cracks in buildings • • Movement of ground and settlement of soil Moisture changes Temp. variation Elastic deformation Creep Chemical reaction Vegetation

Moisture Movement • Reversible Movement - Material expands on absorbing moisture content - Shrinks on drying • Irreversible movement - Material undergo some irreversible movement due to initial moisture change

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Some measures to avoid cracks

Foundation settlement…

Crack due to vegetation…

Identification of cracks: • Careful study of location, width, depthdiagnosis • Observation –stable or temp. • Detection of change of width of cracks due to temp. ---telltales. • Glass piece of flat glass is spanned a/c & tuck to the wall at ends with mortar. • If crack widens it is shown by glass • If shortens then glass will cracks. • Check-super facial /deep. • Fine wire is used to measure the depth.

Repairs of cracks: A) Gunting: • Cleaning of cracks • Filling with thick paste. • Inverted “v” Groove” 10 mm • Mortar of 1: 2

B) Grouting: C) Use of epoxy /polyepoxides.

Types and causes of cracks in Concrete • Before hardening Ø Drying - Plastic shrinkage - Settlement shrinkage - Bleeding - Delayed curing

e… Ø Constructional - Formwork movement - Excess vibration - Subgrade settlement - Finishing Ø Early frost damage

… • After hardening Ø Unsound material Ø Long term drying shrinkage Ø Thermal Ø Moisture movement Ø Biological Ø Structural design deficiencies Ø Chemical Ø Corrosion of reinforcement

Constructional Effects • Crack/Deformation of plastic concrete (After Compaction) -Lack of rigidity of formwork (Remains unnoticed) -Use of high consistency concrete (present trend) : Pumping requirement, Use of superplasticizer -Avoid segregation by proper vibration

Thanks…. .