Seminar On : CAUSES & PREVENTION OF CRACKS IN BUILDINGS
BY : BHAVEK SHARMABTCE
About CRACKS Cracks in buildings are common occurrence. It develops when the stress in a component exceeds the strength.
Classification of Cracks
Structural crack Non Structural crack
o Incorrect designo Faulty constructiono Overloading
o Internal induced stress in building material
Classification of Cracks
Type Width
ThinMediumWide
< 1 mm1-2 mm> 2 mm
VerticalHorizontalDiagonal
StraightToothedSteppedMap patternRandom
Uniform throughoutNarrow at one end and gradually widening at the other
Based on width Based on sight of crack
Outline
Introduction1
Causes of cracks2
Solutions & measures3
Techniques4
Internal stress in Building component
oCompressive oTensileoShearoBuilding material
• Masonry, Concrete, Mortar
• Weak in tension/shear
• Causing tension/shear crack
PRINCIPAL CAUSES OF CRACKS IN BUILDING (Non structural) Thermal variation
Chemical reaction
Moisture movement
Elastic deformation
Creep
Foundation movement & settlement of soil
Vegetation
Manufacturing defects
Details in next few slides
Thermal variation It depends upon: temperature variation, dimensions, co-efficient of expansion, colour, surface
characteristic, thermal conductivity, insulation, internally generated heat etc.
When concreting is done in summer at high temperature, contraction due to drop in temperature in winter is high leading to thermal cracks.
When roof in a load bearing structure
undergoes expansion, horizontal cracks occur
in cross walls as shown :
To prevent thermal variation cracks:
Provision of expansion joints, slip joints, control joints
Slab should be provided thermal insulation.
Span of the slab should not be large.
Slab should either project beyond the wall or rest only partially on the supporting wall.
Shear cracks
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 e.g. Shrinkage of cement on initial drying.
• Initial shrinkage in cement concrete and mortar depends upon: cement & water content, maximum size-grading-quality of aggregates, duration-method-temperature of curing, presence of excessive fines in aggregates, humidity, type of cement, temperature of fresh concrete etc.
Shrinkage cracks
Control shrinkage cracks:
→ Curing for at least 10 days, drying shrinkage is much less.
→ Presence of excessive silt, dust etc in sand and stone aggregates should not exceed 3%.
→ Shrinkage is much less in coastal areas due to high humidity
→ PPC and low grade OPC have much less shrinkage.
→ The ideal temperature range for concreting is 100C to 300C.
→ Sometimes cracks appear on freshly laid concrete even before it sets. This happens when rate of evaporation is higher than bleeding. In such circumstances, concrete should be covered with plastic sheet immediately after concreting and flood cured after initial set has occurred.
Measures to Control cracks (before construction)
In structural concrete shrinkage cracks are controlled by using temperature reinforcement. Even in plain concrete a minimum 0.12% steel is recommended by IS: Codes. It is more effective if smaller diameter bars- closely spaced are used.
Cracks in masonry can be minimized by using rich mortar and delaying plaster work till masonry has dried after curing.
Cement plaster richer than 1:6 is harmful for external wall exposed to high temperature variations, since it will create a stronger membrane than the surface of brick.
Coarse well graded sand should be used for plaster. Fine sand will result in crazy cracks.
Measures to Control cracks (before construction)Strong bond between concrete and plaster prevents shrinkage cracks, if rendering is done as
early as possible after removal of shuttering. Key to plaster is provided by hacking and applying cement slurry just before rendering
Shrinkage cracks affect the appearance and finish and not the structural stability.
Cracks in walls generally get localized at weak sections, such as doors and window openings or staircase walls. In external walls shrinkage cracks generally run downwards from window sill to the lintel of the lower storey.
Construction joint should be avoided in concrete. However if necessary it should be located at one-fourth of span away from preceding beam.
BHAVEK SHARMA
STRUCTURAL CRACKS:
1. Epoxy injection
2. Polyurethane injection
3. Stitching of cracks
Problem Identification & techniques for repairing cracks
Selection of suitable solution for cracks : AFTER CONSTRUCTION
EPOXY INJECTIONo Epoxy Grout Consists Of Epoxy Resin,
Epoxy Hardener And Sand/Aggregates.
oEpoxy Grout Is Non-porous And
Wouldn’t Absorb Any Contaminant Or
Stains
STRUCTURAL CRACKS:
1. Epoxy injection
3. Stitching of cracks
2. Polyurethane Injection
BHAVEK SHARMA
Problem Identification & techniques for repairing cracks
Selection of suitable solution for cracks : AFTER CONSTRUCTION
POLYURETHANE INJECTION Polyurethane injection involves a high
pressure (typically 1500-3200 psi) injection of activated polyurethane through injection packers hammered into drilled holes.
These fast-setting foams are effective alternatives for applications involving only crack sealing (waterproofing) and not structural repair.
Installed Injection Packer
Polyurethane Crack Injection
STRUCTURAL CRACKS:
1. Epoxy injection
2. Polyurethane Injection
3. Stitching of cracks
BHAVEK SHARMA
Problem Identification & techniques for repairing cracks
Selection of suitable solution for cracks : AFTER CONSTRUCTION
Stitching of cracks
Thank you
"SOMEWHERE, SOMETHING INCREDIBLE IS WAITING TO BE KNOWN."
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