The document discusses different types of cracks that can occur in concrete structures, including cracks in fresh/plastic concrete caused by shrinkage or formwork movement, and cracks in hardened concrete caused by drying shrinkage, thermal stresses, chemical reactions, corrosion of reinforcement, poor construction practices, errors in design/detailing, or external loads. It classifies cracks by width and effect, and explains some common causes of cracks like plastic shrinkage, corrosion, overloading, and thermal stresses.

2.  All structures will develop some cracks both structural and non structural.
 Most of them are non essential and no need to worry about that. But some
cracks may be an indication of a larger problem underneath and can be
corrected.
“A crack is a complete or incomplete
separation of concrete into two or
more parts produced by breaking or
fracturing”

6. Fine < 0.1mm
Thin 0.1 to 0.3mm
Medium 0.3 to 0.7mm
Wide 0.7 to 2mm
Very wide > 2mm
Classification of cracks based on their crack width:

7. Classification of cracks based on their effects:
Class I-Cracks leading to Structural Failure
Class II Cracks causing Corrosion
Class III-cracks affecting Function
Class IV-cracks affecting appearance

10. Cracks in Fresh or Plastic Concrete
1. Plastic shrinkage Cracks
2. Plastic Settlement Cracks
3. Cracks caused by formwork movement
Cracks in Hardened Concrete
1. Drying Shrinkage Cracks
2. Cracks due to Thermal Stresses
3. Cracks due to Chemical Reaction
4. Weathering Cracks
5. Corrosion of Reinforcement
6. Poor Construction Practices
7. Construction Overloads
8. Errors in Design and Detailing
9. Externally Applied Loads

11. Cracks in Fresh or Plastic Concrete
1. Plastic shrinkage Cracks
 It arises when the rate of evaporation of water from top layer of freshly laid
concrete is greater than bleed water provided by underlying concrete, due to
this surface concrete contracts.
 This leads to shallow crack formation of polygonal shape or parallel to one
another. These are minor cracks and does not harm the structure.

14. 2. Plastic Settlement Cracks
Cracks in Fresh or Plastic Concrete

15. After initial placement, vibration, and finishing, concrete has a tendency to continue to
consolidate. During this period, the plastic concrete may be locally restrained by reinforcing
steel, a prior concrete placement, or formwork. This local restraint may result in voids
and/or cracks adjacent to the restraining element

16. 3. Cracks caused by formwork movement
Cracks in Fresh or Plastic Concrete

17. Cracks in Hardened Concrete
1. Drying Shrinkage Cracks

21.  Crazing is the development of fine networks of random
cracks on the surface of concrete caused by shrinkage of
surface layer.
 Crazing of concrete develop at an early age and its very hard
to detect unless wet and beginning to dry.
 They do not affect the structural integrity of the structure or
durability of the concrete.
Crazing

23. 2. Cracks due to Thermal Stresses

26. 3. Cracks due to Chemical Reaction

28. 4. Weathering Cracks

29. 5. Corrosion of Reinforcement
 In most of the cases the damage of concrete is due to
corrosion of reinforcement. Corrosion process in concrete
begins with penetration of various aggressive agents, low
permeability is the key to solve this problem.
 Concrete permeability depends upon water-cement ratio,
curing and correct compaction. A well designed concrete is
water tight and adequate cover gives good protection to
reinforcements from corrosion.
 Reinforcement corrosion is very hard to repair and corrosion
of reinforcement causes severe cracks with a brownish color.
This leads to loss of strength and finally collapse.

30. 6. Poor Construction Practices

31.  Loads induced during construction can often be far more severe than those experienced
in service. Unfortunately, these conditions may occur at early ages when the concrete is
most susceptible to damage and they often result in permanent cracks.
 Precast members, such as beams and panels, are most frequently subject to this
abuse, but cast-in-place concrete can also be affected. A common error occurs when
precast members are not properly supported during transport and erection. The use of
arbitrary or convenient lifting points may cause severe damage.
7. Construction Overloads

32.  The effects of improper design and/or detailing range from
poor appearance to lack of serviceability to catastrophic
failure. These problems can be minimized only by a thorough
understanding of structural behavior
 Errors in design and detailing that may result in unacceptable
cracking include use of poorly detailed reentrant corners in
walls, precast members and slabs, improper selection and/or
detailing of reinforcement, restraint of members subjected to
volume changes caused by variations in temperature and
moisture, lack of adequate contraction joints, and improper
design of foundations, resulting in differential movement
within the structure.
8. Errors in Design and Detailing

34.  Most concrete structures are susceptible to external loads that induce tensile stresses
through their concrete members.
 It is important to deal with these loads in the most effective way, so try to disperse the
load evenly across the individual members to reduce the risk of uncontrolled
cracking.
 Factors that can reduce cracks’ widths are an increased amount of steel
reinforcement and larger concrete sections to disperse the loads more evenly.
9. Externally Applied Loads