CRACKS IN CONCRETE STRUCTURE AND THEIR CAUSES What is crack Classification of Cracks - Structural cracks - Non structural cracks

1. Maintenance &
Rehabilitation of Structures
Subject code: 3360605

2. CRACKS IN CONCRETE
STRUCTURE AND THEIR
CAUSES
SEMINAR ON:

3. About CRACKS
What is CRACK?
Break or cause to break without a complete
separation of the parts.
• Cracks in the building are common occurrence.
• It develops hen the stress in a component exceeds the
strength.

4. Classification of Cracks

5. Non-Structural Cracks
Non-structural cracks are not of so much
significance as far as safety is considered but it deals more
with aesthetic point of view.
Cause:
 Due to stresses produced in a member, mainly
• Tensile stresses
• Shear stresses

6. Tensile Cracks

7. Shear Cracks

8. Cracks in Concrete
 Causes of cracking:
A. Cracking which occurs in plastic concrete
• Plastic shrinkage cracking
• Settlement cracking
B. Cracking which occurs in hardened concrete
• Drying shrinkage
• Thermal stress
• Chemical reaction
• Weathering
• Corrosion of Reinforcement
• Poor construction Practice
• Structural Overload
• Error in Design and Detailing

9. Plastic Shrinkage Cracking
• Occurs due to very rapid loss of moisture
• Factors including air and concrete temperature, relative
humidity and wind velocity
• It occurs prior to final setting

10. Settlement Cracking
• Occurs when the settlement of
concrete is blocked by
reinforcement, framework etc.
• Due to restraints; cracks
develops in structure which
are adjacent to restraining
element
• It increase with increase in bar
size, inadequate vibration and
increase in slump
• It decreases with increase in
size of cover and addition of
fibers in concrete.

11. Drying Shrinkage
• Caused by loss of moisture
form the cement paste
constituent
• It is the combination of
shrinkage and restraint that
causes tensile stress
• Contraction joints and
correct detailing of the
reinforcement reduces
shrinkage cracking.

12. Chemical Reactions
• Occur due to reaction of concrete in its firm state with
materials used to make concrete or by materials that
came in contact with it
• Concrete get cracked when concrete react with
aggregate containing active-silica and alkalis resulting
from cement hydration
• Mainly due to alkalis, active silica and sulfates
Weathering
• Weathering is wear and tear of structures caused by
freezing, drying and wetting of concrete
• Concrete can be protected against weathering by use of
the low w/c ratio, tough aggregate and adequate curing
of concrete.

13. Corrosion of reinforcement
• Due to oxidation of reinforcement bars in existence of
moisture which increases its volume
• A bursting radial stresses are produced around bars which
result in local radial cracks around bars.
• Remedial technique comprises of epoxy coating of bars,
use of richer grade of concrete and by use of corrosion
inhibitors.

14. Poor Construction Practice
• In this the most common is additional of water to
increase workability
• It plays an important role in decreasing concrete
strength, increasing concrete settlement and increasing
drying shrinkage of concrete.
• Another problem which comes under this is when less
curing is done or curing is eliminated early stages.
Weathering
• Weathering is wear and tear of structures caused by
freezing, drying and wetting of concrete
• Concrete can be protected against weathering by use of
the low w/c ratio, tough aggregate and adequate curing
of concrete.

15. Structural Overloads
• Concrete gets damaged due to structural overload which
are very easy to detect.
• Precast member like beam and are generally subjected
to this type of load.
• These types of cracks can be prevented if designer limit
the load on structure.
Errors in Design and Detailing
• Errors in detailing & designing result in cracking of
concrete
• It include incorrect detailing of reinforcement steel bars
and others problems like restraint of members, lack of
adequate contraction joints and incorrect design of
foundations etc.

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