Amit Payal

1. Submitted By:-
Amit Payal-TO
Types of cracks and
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 totalling 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. Nonstructuralcracks
•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
Stitching
Routing and sealing
Resin injection
Dry packing
Polymer impregnation
Vacuum impregnation
Autogenously healing
Flexible sealing
Drilling and plugging
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:
The surface of cracks is cleaned and all the loose materials are removed. These are then filled
with quick setting cement mortar.
 For cracks which are very large, filler materials such as stone chips can be used.
 Additional reinforcement and shear reinforcements can be used for heavily damaged concrete
members or wherever necessary based on requirements.
 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.