seminar related ppt for 15minutes for cracks

1. Seminar On :
CAUSES & PREVENTION OF CRACKS IN
BUILDINGS
BY : BHAVEK SHARMA
BTCE

2. 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 design
o Faulty construction
o Overloading
o Internal induced stress
in building material

3. Classification of Cracks
Type Width
Thin
Medium
Wide
< 1 mm
1-2 mm
> 2 mm
Vertical
Horizontal
Diagonal
Straight
Toothed
Stepped
Map pattern
Random
Uniform
throughout
Narrow at
one end and
gradually
widening at
the other
Based on width Based on sight of crack

4. Outline
Introduction1
Causes of cracks2
Solutions & measures3
Techniques4

5. Internal stress in Building component
oCompressive
oTensile
oShear
oBuilding material
• Masonry, Concrete, Mortar
• Weak in tension/shear
• Causing tension/shear crack

6. 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

7. 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 :

8. 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.

9. Shear cracks

10. 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.

11. Shrinkage cracks

12. 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.

13. 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.

14. 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.

15. 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
BHAVEK SHARMA

16. EPOXY INJECTION
o Epoxy Grout Consists Of Epoxy Resin,
Epoxy Hardener And Sand/Aggregates.
oEpoxy Grout Is Non-porous And
Wouldn’t Absorb Any Contaminant Or
Stains

17. 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

18. 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

19. 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

20. Thank you
"SOMEWHERE, SOMETHING INCREDIBLE IS WAITING TO BE KNOWN."