Cracks in Concrete

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Cracks in Concrete



2
-
Classifications



3
-
Concrete removal, preparation



4
-
References

Cracks in Concrete



1
-
lntroduction



1
-
lntroduction







the concrete cracks are caused due to many reasons as
repeated thermal cycle, accidental overloading, drying
shrinkage, inadequate design or construction, or some
other causes .

This seminar is to provide guidance on classification of
concrete cracks and discusses removal of the existing
concrete ,preparation of concrete surface to receive repair
materials and methods for repairing the reinforcement
bars .

2
-
Classifications



2
-
1
SHRINKAGE CRACKS.


2
-
2
CRACKS DUE TO CARBONATION OF CONCRETE.


2
-
3
CRACKS IN REINFORCED SLABS.


2
-
4
CRACKS IN BEAMS.


2
-
5
CRACKS IN COLOUMNS.


2
-
6
CRACKS IN REINFORCED

WALL .


2
-
7
CRACKS DUE TO STRUCTURAL PROBLEMS.



2
-
Classifications



2
-
1
SHRINKAGE CRACKS.

Common crack is shown widely in walls and slabs so must
put joint every
12
m ,

And for cover of reinforcement bars when it is more than
4
cm or less than
1
cm so must put mesh of wires and
improve the mix.

2
-
Classifications



2
-
2
CRACKS DUE TO CARBONATION OF CONCRETE.

Especially in coastal area the carbonation of concrete allows
humidity to reach to the bars then corrosion will occur.

So must make cover of bars more than
4
cm and paint the
concrete and improve the mix.

2
-
Classifications



2
-
3
CRACKS IN BEAMS.

2
-
3
-
1
thermal Cracks :

As vertical cracks through total

height of beam and same thickness


and in L/
5
of beam near support ;




2
-
3
-
2
Bending Cracks :

These cracks exist in maximum


moment zones at middle of span

and at support

2
-
Classifications



2
-
3
CRACKS IN BEAMS.

2
-
3
-
3
shear Cracks :

Cracks at
45
with horizontal axis


(diagonal tension )

Reason : shear reinforcement is less than required.



2
-
3
-
4
Torsion Cracks :

Continuous Cracks at
45
with horizontal axis


(diagonal tension )


2
-
Classifications



2
-
4
CRACKS IN COLOUMNS.

2
-
4
-
1
Bending Cracks :

These cracks exist in maximum


moment zones


2
-
4
-
2
Cracks due to stirrups :

Vertical Cracks

Reason : lateral tension




2
-
4
-
3
Cracks due to settlement :

Horizontal Cracks

Reason : tension force because

Horizontal or vertical movement

Of foundation.


2
-
Classifications



2
-
5
CRACKS IN REINFORCED SLABS.


Reason : the reinforcement bars is

less than required .



2
-
Classifications



2
-
6
CRACKS IN REINFORCED

WALL .


2
-
6
-
1
Bending Cracks :

These cracks exist in maximum


moment zones when wall does as beam


2
-
6
-
2
shear Cracks :

Cracks at
45
with horizontal axis


(diagonal tension )




2
-
6
-
3
Cracks due to weight :

Horizontal Cracks


2
-
Classifications



2
-
7
CRACKS due to structural problems .


3
-
Concrete removal, preparation


3.1
-
Surface preparation

Methods of surface preparation
-
Typical methods

a)
Chemical cleaning
.


In most cases chemical cleaning methods of surface preparation are not appropriate for
use with the Concrete repair materials. However, with certain coatings under certain
conditions, it may be possible to use detergents, phosphate, and various proprietary
concrete cleaners.

it is important that all traces of the cleaning agent be removed after the contaminating
material is removed.

b)
Acid etching
. Acid etching of concrete surfaces has long been used to remove

laitance and normal amounts of dirt. The acid will remove enough cement paste


to provide a roughened surface which will improve the bond of replacement materials.


c)
Mechanical preparation
. This technique consists of mechanically removing thin

layers of surface concrete

using such equipment as impacting tools (breakers.

scabblers), grinders, and scarifier. Depending on the equipment used, a variety of


surfaces may be obtained.

d)
Abrasive preparation
. This technique consists of removing thin layers of

surface concrete using abrasive equipment such as sandblasters, shotblasters,


or high pressure water blasters.

3
-
Concrete removal, preparation

3.1
-
surface preparation

3.2
-
Reinforcement repair

3.2.1
Removal of concrete surrounding steel

removal of the deteriorated concrete surrounding the reinforcement.


3.2.2
Quantity to remove.


All weak, damaged and easily removable concrete should be chipped
away.


3.2.3
Inspection of reinforcing steel

steel is capable of performing as intended by the designer.


3.2.4
Cleaning of reinforcement steel .


4
-
References


1
-
CONCRETE REPAIR MANUAL VOLUME
1
….ACI,ICRI,BRE,CS.
2003
USA


2
-
DETERIORATION AND REPAIR OF REINFORCED CONCRETE


IN THE ARABIAN GULF VOLUME
1
1989
. Bahrain


3
-
CRACKS IN REINFORCED CONCRETE

STRUCTURES
1997
EYGPT



4
-
REASONS OF BUILDINGS COLLAPSE
1999
EYGPT



5
-
STRUCTURAL EVALUATION

1998

SYRIA


6
-
REHABILITATION OF BUILDING

2000

SYRIA