this presentation deals with the different types of cracks generated in concrete during its usage and after its application and also methods to retrofit these cracks

1. cracks
Introduction
Types of cracks
Repairing techniques

2. introduction
• If this stress and the restrained strain are allowed
to develop to such an extent that they exceed the
strength or strain capacity of concrete, then cracks
will take place.
• Generally, 1/16 to 1/4-inch-wide cracks is
acceptable limits (if its not leaking water).
• A 100-foot-long regular-weight concrete slab
normally would shrink by about 3/4 inch. In other
words, you should expect cracks totaling in
widths up to 3/4 inch in every 100 feet of
concrete.

3. TYPES OF CRACKS
Structural Cracks
Structural cracks are those which result from
incorrect design, faulty construction or overloading
and these may endanger the safety of a building.
Non-Structural Cracks
Non Structural cracks occur mostly due to internally
induced stresses in building materials. These cracks
normally do not endanger the safety but may look
unsightly, create an impression of faulty work or
give a feeling of instability.

4. Non structural cracks
• Plastic shrinkage cracks
• Cracking caused by plastic shrinkage in concrete occurs
most commonly on the exposed surfaces of freshly placed
floors and slabs with large surface areas when they are
subjected to a very rapid loss of moisture caused by low
humidity and wind or high temperature or both.
• Plastic shrinkage usually occurs prior to final finishing,
before curing starts. When moisture evaporates from the
surface of freshly placed concrete faster than it is placed by
curing water, the surface concrete shrinks.
• In most cases, these cracks are wide at the surface. They
range from a few millimeters to many meters in length and
are spaced from a few centimeters to as much as 3 m apart.

5. Hairline cracks
• cracks may develop in concrete foundations as
the concrete cures is called hairline cracks.
• If the cracks appear shortly after pouring the
concrete foundation, concrete may have been
mixed poorly or poured too quickly. In poured
concrete foundations, hairline crack
frequently appear in the center of the walls
because the wall corners have a greater
stability.

6. Settlement cracks
• They appear when the underlying ground has
not been compacted or prepared properly or
if the subsoil was not of the proper
consistency.
• Settlement cracks are usually wider at the top
of the crack than the bottom as the
foundation "bends" over a single point,
allowing differential settlement.

7. Thermal Cracking of Concrete
• Temperature difference within a concrete structure
may be caused by portions of the structure losing heat
of hydration at different rates or by the weather
conditions cooling or heating one portion of the
structure to a different degree or at a different rate
than another portion of the structure.
• These temperature differences result in differential
volume change, leading to cracks. This is normally
associated with mass concrete including large and
thicker sections of column, beams and slabs

8. Repairing techniques
i) Stitching
ii) Routing and sealing
iii) Resin injection
iv) Dry packing
v) Polymer impregnation
vi) Vacuum impregnation
vii) Autogenous healing
viii) Flexible sealing
ix) Drilling and plugging
x) Bandaging

9. STITCHING
 In this technique, the crack is bridged with U-shaped metal units
called stitching dogs before being repaired with a rigid resin material.
 A non- shrink grout or an epoxy resin based adhesive should be used
to anchor the legs of the dogs.
 Stitching is suitable when tensile strength must be
re established across major cracks.
 Stitching dogs should be of variable length and orientation.
• The stitching of cracks is not a method of crack repair or to gain the lost
strength, this method is used to prevent the cracks from propagating and
widening.

10. ROUTING AND SEALING
 This is the simplest and most common method of crack repair.
 It can be executed with relatively unskilled labor and can be
used to seal both fine pattern cracks and larger isolated cracks.
 This involves enlarging the crack along its exposed
face(routing) and sealing it with crack fillers.
 Care should be taken to ensure that the entire crack is routed
and sealed.

11. RESIN INJECTION
• The smaller cracks less than 0.75 mm width can be
effectively repair by using pressure injection of epoxy.
• Surface of the member near cracks is thoroughly cleaned.
• Loose materials are removed and plastic injection ports are
placed along the length of crack.
• These ports are placed on both sides of the member and
secured in placed with the help of epoxy seal.
• Low viscosity resin is injected into one port at a time
starting from the port at lowest level and moving upwards.
• This method can be used for all types of structural members
such are beams, columns, walls and slabs.

12. Repair of Large Cracks Concrete:
• 1)The surface of cracks is cleaned and all the
loose materials are removed. These are then
filled with quick setting cement mortar.
• 2) For cracks which are very large, filler
materials such as stone chips can be used.
• 3) Additional reinforcement and shear
reinforcements can be used for heavily
damaged concrete members or wherever
necessary based on requirements.

13. Cont….
• 4) For damaged walls and roofs, additional
reinforcement in the form of mesh is used on
one side or both sides of the members. These
mesh should sufficiently tied with existing
members.