Repairs and rehabilitation of structuresRepairs and rehabilitation of structures

1. REPAIRS AND REHABILITATION OF
STRUCTURES
MATERIALS AND TECHNIQUES FOR
REPAIR

2. SPECIAL TYPES OF CONCRETE:
-with out-of-the-ordinary properties or
those produced by unusual techniques.
Light: Transparent Concrete

3. STRUCTURAL LIGHTWEIGHT CONCRETE
Structural lightweight concrete is similar to
normal- weight concrete except that
-it has a lower density.
-it is made with lightweight
aggregates or
-it is made with a combination of
lightweight and normal- weight aggregates.
Lightweight concrete

4. The term "sand lightweight“ - made with
coarse lightweight aggregate and natural
sand.
Structural lightweight concrete has
-air-dry density in the range of 1350 to
1850 kg/m3
-28-day compressive strength in excess of
17 MPa
sand sandwich board light weight concrete

5. -for comparison, normal-weight concrete
containing regular sand, gravel, or crushed
stone has a dry density in the range of 2080
to 2480 kg/m3
Structural lightweight concrete is used
primarily to reduce the dead-load weight in
concrete members, such as floors in high-
rise buildings.

6. Structural Lightweight Aggregates
-usually classified
according to their production process
because various processes produce
aggregates with somewhat different
properties, which includes:
•Rotary kiln expanded clays, shales, and
slates
Chipped ShaleExpanded clay Expanded slate

7. •Sintering grate expanded shale and slates
•Pelletized or extruded fly ash
•Expanded slag
Fly ash Pellet Expanded slag

8. •Structural lightweight aggregates can also be
produced by processing other types of
material, such as naturally occurring pumice
and scoria.
Pumice scoria

9. •Structural lightweight aggregates have
densities significantly lower than normal-
weight aggregates, ranging from 560 to 1120
kg/m3
, compared to 1200 to 1760 kg/m3
for
normal-weight aggregates.
•These aggregates may absorb 5% to 20%
water by weight of dry material.
•To control the uniformity of structural
lightweight concrete mixtures, the aggregates
are pre wetted (but not saturated) prior to
batching.

10. HIGH-DENSITY CONCRETE
High-density (heavyweight) concrete has a density of up
to about 6400 kg/m3
.
Heavyweight concrete used for radiation shielding
As a shielding material, heavyweight concrete protects
against the harmful effects of X-rays, gamma rays, and
neutron radiation.
Heavyweight concrete to protect & shield places with
greater risk of radiation.

11. Selection of concrete for radiation shielding
is based on space requirements and on the type
and intensity of radiation.
Where space requirements are not important,
normal-weight concrete will generally produce
the most economical shield;
Where space is limited, heavyweight
concrete will allow for reductions in shield
thickness without sacrificing shielding
effectiveness.

12. Properties of High-Density Concrete
•Both the freshly mixed and hardened states can meet
job conditions and shielding requirements by proper
selection of materials and mixture proportions.
•Except density, the physical properties are similar to
normal-weight concrete.
•Strength is a function of water-cement ratio; thus, for
any particular set of materials, strengths comparable
to those of normal-weight concretes can be achieved.
•radiation shield has special requirements, trial
mixtures should be made with job materials and
under job conditions to determine suitable mixture
proportions.

13. EXPANSIVE CEMENT:
Concrete made with ordinary Portland cement shrinks
due to loss of free water. Concrete also shrinks continuously
for long time. This is known as drying shrinkage.
Cement used for
-grouting anchor bolts or
-grouting machine foundations or
-grouting the prestress concrete ducts, if
shrinks,
There has been a search for such type of cement which
will not shrink while hardening and thereafter.
As a matter of fact, a slight expansion with time will
prove to be advantageous for grouting purpose.
This type of cement which suffers no overall change in
volume on drying is known as expansive cement.

14. Cement of this type has been developed by using an
expanding agent and a stabilizer very carefully.
Proper material and controlled proportioning are necessary
in order to obtain the desired expansion.
One type of expansive cement is known as shrinkage
compensating cement.
This cement when used in concrete, with restrained
expansion, induces compressive stresses which approximately
offset the tensile stress induced by shrinkage.
Another similar type of cement is known as self-stressing
cement. This cement when used in concrete induces
significant compressive stresses after the drying shrinkage has
occurred. Fibre content :0.5 to 2.5% by volume of mix

15. POLYMER CONCRETE:
Continuous research by technologists to understand,
improve and develop the properties of concrete has resulted
in a new type of concrete known as “polymer concrete”.
This concrete is porous in nature and this porosity due to
air-voids, water voids or due to the inherent porosity of gel
structure itself.
The development of concrete-polymer composite
material is directed at producing a new material by
combining the ancient technology of cement concrete with
the modern technology of polymer chemistry.

16. TYPES OF POLYMER CONCRETE:
Four types of polymer concrete materials are
being developed,
•Polymer Impregnated Concrete(PIC)
•Polymer Cement Concrete(PCC)
•Polymer Concrete(PC)
•Partially Impregnated and Surface coated
polymer concrete

17. POLYMER IMPREGNATED CONCRETE (PIC):
The monomers used in this type are,
•Methylmethacrylate(MMA)
•Styrene
•Acrylonitrile
•t-butyl styrene
•Other thermoplastic monomers
POLYMER CEMENT CONCRETE (PCC)
The monomers that are used in PCC are,
•Polyster-styrene
•Epoxy-styrene
•Furans
•Vinylidene chloride

18. APPLICATIONS OF POLYMER
IMPREGNATED CONCRETE:
The following are the application of the PIC,
•Prefabricated structural elements
•Prestressed concrete
•Marine works
•Desalination plants
•Nuclear power plants
•Sewage works-pipe and disposal works
• Ferrocement products
•For water proofing of structure
•Industrial applications

19. •SULPHUR-INFILTERATED CONCRETE:
•New types of composites have been produced by the recently developed
techniques of impregnating porous materials like concrete with sulphur.
Sulphur impregnation has shown great improvement in strength.
•In the past, some attempts have been made to use sulphur as a binding
material instead of cement.
•Sulphur is heated to bring it into molten condition to which cores and
fine aggregates are pored and mixed together.
•On cooling, this mixture gave fairly good strength, exhibited acid
resistance and also other chemical resistance, but it proved to be costlier
than ordinary cement concrete.
•Recently, use of sulphur was made to impregnate lean porous concrete
to improve its strength and other useful properties considerably.
•In this method, the quantity of sulphur used is also comparatively less
and thereby the processes is made economical.
•It is reported that compressive strength of about 100MPa
could be
achieved in about two days time.

20. •Two procedures are adapted “A” after 24hours of moist curing, the
specimen is dried in heating cabinet for 24hours at 1210
C.
•Then the dried specimens are placed in a container of molten
sulphur at 1210
C for 3 hours.
•Specimens are removed from the container, wiped clean of sulphur
and cooled to room temperature for 1hour and weighed to determine
the weight of sulphur in filtrated concrete.
•In procedure “B”, the dried concrete specimen is placed in an
airtight container and subjected to vacuum pressure of 2mm mercury
for 2hours.
•After removing the vacuum, the specimens are soaked in the molten
sulphur at atmospheric pressure for another half an hour.
• The specimen is taken out, wiped clean and cooled to room
temperature in about 1hour.The specimen is weighed and the
weight of sulphur-impregnated concrete is determined.

21. FERROCEMENT CONCRETE:
• Ferro-cement technique though of recent origin, have been
extensively used in many countries, notably in U.K., New Zealand and
China.
•There is a growing awareness of the advantages of this technique of
construction all over the world.
•It is well known that conventional reinforced concrete members are too
heavy, brittle cannot be satisfactorily repaired if damaged, develop
cracks and reinforcements are
liable to be corroded.
•Ferrocement is a relatively new material consisting of wire meshes and
cement mortar. It consists of closely spaced wire meshes which are
impregnated with rich cement
mortar mix.
•The wire mesh is usually of 0.5 to 1.0mm dia wire at 10mm spacing and
cement mortar is of sand ratio of 1:2 or 1:3 with water /cement ratio of
0.4 to 0.45.

22. •The ferrocement elements are usually of the order of 2 to 3cm in
thickness with 2 to 3mm external cover to the reinforcement.
•The steel content varies between 300kg to 500kg per cubic meter of
mortar.
•The main advantages are simplicity of its construction, lesser dead
weight of the elements due to their small thickness, its high tensile
strength, less crack widths compared to conventional concrete, easy
reparability, non corrosive nature and easier mould ability to any
required shape.
•There also saving in basic materials namely cement and steel. This
material is more suitable to special structures like shells which have
strength through forms and structures like roofs, silos, water tanks and
pipelines.
•The development of ferrocement depends on suitable casting techniques
for the required shape. Development of proper prefabrication techniques
for ferrocement is still not a widely explored area and gap needs to be
filled.

23. FIBRE REINFORCED CONRETE:
•Plain concrete possess a very low tensile strength, limited
ductility and little resistance to cracking.
•Internal micro cracks are inherently present in the concrete
and its poor tensile strength due to the propagation of such
micro cracks, eventually leading to brittle fracture of the
concrete.
•In plain concrete and similar brittle materials, structural
cracks(micro-cracks) develop even before loading, particularly
due to drying shrinkage or other causes of volume change.
•When loaded, the micro cracks propagate and open up, and
owing to the effect of stress concentration, additional cracks
form in places of minor defects.
•The development of such microcracks is the main cause of
inelastic deformations in concrete.

24. •It has been recognized that the addition of small,
closely spaced and uniformly dispersed fibres to
concrete would act as crack arrester and would
substantially improve its static and dynamic
properties. This type of concrete is known as Fibre
Reinforced Concrete.
•Fibre Reinforced Concrete can be defined as a
composite material consisting of mixture of cement,
mortar or concrete and discontinuous, discrete,
uniformly dispersed suitable fibres.
•Continuous meshes, woven fabrics and long wires or
rods are not considered to be discrete fibres

25. FIBRES USED:
•Many types of fibres used in cement and concrete,
not all of them can be effectively and economically
used. Each type of fibre has its characteristics
properties and limitations.
•Some of the fibres that could be used are steel fibres,
polypropylene, nylons, asbestos, coir, glass and
carbon.
•The fibre is often described by a convenient
parameter called “Aspect ratio”. The aspect ratio of
the fibre is the ratio of its length to its diameter. It
ranges from 30 to 150.

26. •Steel fibres are most commonly used and the diameter may
vary from 0.25 to 0.75mm.
•Glass fibre is a recent introduction in making fibre
concrete. It has tensile strength of about 1020 to
4080N/mm²
•Polypropylene and nylon fibres are found to be suitable to
increase the impact strength. They posses high tensile
strength, but their low modulus of elasticity and higher
elongation do not contribute to the flexural strength.
•Asbestos is a mineral fibre and has proved to be most
successful of all fibres as it can be mixed with Portland
Cement. Tensile strength would be from 560 to 980N/mm².
•Carbon fibres perhaps posses very high tensile strength
2110 to 2815N/mm².