This document discusses techniques for repairing, rehabilitating, and retrofitting structures. It covers strengthening structural elements, repairing structures damaged by corrosion, fire, leakage, or earthquakes. Specific techniques addressed include repairing fire-damaged concrete, sealing leaks, repairing cracks, jacketing structural members, and dry packing. The document also covers engineered demolition methods like mechanical demolition, implosion, and deconstruction for taking down structures.

1. UNIT V
REPAIR, REHABILITATION AND
RETROFITTING OF STRUCTURES
PREPARED BY
MYTHILI D
AP CIVIL
EXCEL ENGINEERING COLLEGE

2. Strengthening of Structural elements, Repair of
structures distressed due to corrosion, fire,
Leakage, earthquake – DEMOLITION
TECHNIQUES - Engineered demolition
methods - Case studies.

3. Need for Strengthening
• Load increases due to higher live loads, increased wheel
loads, installations of heavy machinery or vibrations
• Damage to structural parts due to aging of construction
materials or fire damage, corrosion of the steel
reinforcement, and impact of vehicles
• Improvements insatiably for use due to limitation of
deflections, reduction of stress in steel reinforcement and
reduction of crack widths
• Special Modification of structural system due to the
elimination of walls/columns and openings cut through
slabs.
• Errors in planning or construction due to insufficient design
dimensions and insufficient reinforcing steel.

7. Restoration of fire Damaged Elements
• The eccentrically loaded columns fail when
reinforcement bars in tension heat up.
• The fire resistance of such elements can be increased
by increasing the thickness of protective layer.
• Heat transmission and temperature of bottom
reinforcement are keys to the behavior of reinforced
concrete slab exposed to fire.
• The reinforcing bars are assumed to retain one half of
their original strength. Carrying capacity of slabs can be
enhanced by increasing their thickness. For beams,
depth and width can be increased.

8. Restoration of fire Damaged Elements
• It should be kept in mind that in beams,
weakening of bond between transverse
reinforcement and concrete on account of
heating reduces the residual shear load carrying
capacity considerably. The carrying capacity of
axially loaded depends upon the cross section of
the column coefficient of change in strength of
concrete under high temperature and
corresponding critical temperature. The carrying
capacity can be restored by increasing the cross
section with suitable increase in the longitudinal
steel.

9. Leakages in the concrete structures
• It causes inevitable damage to the reinforcement.
Construction joints, shrinkage and restraint cracks may
form leak paths. The amounts of water involved vary from
damp-patches which tend to evaporate as they are formed,
to running –leaks which may eventually form undrained
surfaces.
• Damp patches may also be formed when water passes
through the voids along reinforcing bars formed due to
plastic settlement. The other common routes for larger
volume leaks are honeycombed concrete, movements
joints like expansion and contraction joints. In case of
water-retaining structures, the extent of leakage may be
measured by monitoring loss of liquid from the structure.

10. Techniques
• Conventional leak-sealing methods
• Leak-sealing by injection techniques

11. Conventional leak-sealing methods
• Surface preparations
• Filling of surface imperfections with resin-
based grouts
• Application of primer
• Application of two coats of high-build paint

12. Injection Sealing
• From liquid flow and pressure considerations the
simplest and most cost effective way is to seal the
leakage from the water-retaining side of the
structure. When the wet side is inaccessible, the
leakage must be tackled from the dry side which
is considerably more difficult.Successfull leak
sealing requires injection of sealant to fill water
passages completely, and it is necessary to attain
a relatively high flow velocity to achieve this,
because of short pot-life or working time of the
typical repair material.

13. Marine exposure
• Durability of concrete exposed to sea-water
again stresses that of all chemical and physical
properties, permeability of concrete is the
most important factor influencing
performance. Concrete are achieved by using
mixes having high cement contents and low
water: cement ratios, through consolidation
and control of thermal and shrinkage cracking,
and limiting cracks due to mechanical loading.

14. techniques required for repairing
cracks
• Bonding with epoxies
• Routing and sealing
• Stitching
• Blanketing
• External stressing
• Grouting
• Autogenous healing

15. Bonding with epoxies
• These are organic compound which when
activated with suitable hardening agents form
strong chemically resistant structures having
excellent adhesive properties. They are used
as binders or adhesives to bond new concrete
patches to existing surfaces or hand together
cracked portions. Once hardened, this
compound will not melt, flow or bleed. Care
should be taken to place the epoxy within the
pot life period after mixing.

16. Routing and sealing
• This method involves enlarging the cracks
along its exposed surface, filling and finally
sealing it with a suitable material. This is the
simplest and most common technique for
sealing cracks and is applicable for sealing
both fine pattern cracks and larger isolated.

17. Stitching
• The tensile strength of a cracked concrete
section can be restored by stitching in a
manner similar to sewing cloth.

18. Blanketing
• This is the simplest and most common
technique for sealing cracks and is applicable
for sealing both fine pattern cracks and larger
isolated. The cracks should be dormant unless
they are opened up enough to put in a
substantial paten in which case the repair may
be more property termed as “Blanketing”.

19. External stressing
• Development of cracking in concrete is due to
tensile stress and can be arrested by removing
these stresses. Further the cracks can be
closed by including a compressive force
sufficient to over come the tension a residual
compression.

20. Grouting
• Grouting can be performed in a similar
manner as the injection of an epoxy. However
the use of an epoxy is the better solution
except where considerations for the resistance
of cold weather prevent such use in which
case grouting is the comparable alternative.

21. Autogenous healing
• The inherent ability of concrete to heal cracks
within “autogenous healing”. This is used for
sealing dormant cracks such as precast units
cracked in handling of cracks developed
during the precast pilling sealing of cracks in
water hands and sealing of cracks results of
temporary conditions.

22. Jacketing
• It consists of restoring or increasing the
section of an existing member by encasing it
in a new concrete. This method is useful for
protection of section against further
deterioration by providing additional to in
member.

23. Dry packing
• Dry packing is the hand placement of a very
dry mortar and subsequent tamping or
ramming of the mortar into place producing
an intimate contact between the old and new
concrete work.

24. causes of cracks
• Use of unsound material
• Poor & bad workmanship
• Use of high water-cement ratio
• Freezing & thawing
• Thermal effects
• Shrinkage stresses

25. types of cracks
• a) Class-1: Cracks leading to structural failure
b) Class-2: Cracks causing corrosion
• c) Class-3: Cracks affecting function
• d) Class-4: Cracks affecting appearance

26. Demolition techniques
• Non Engineering Demolition
Manual Demolition
• Engineering Demolition
Mechanical Method
Implosion
Deconstruction Method

27. Non Engineering Demolition
• This is normally carried out by contractors
using manual tool which is portable, tools
used are Sledge Hammer, Jack Hammers and
Drillers.

28. Jack Hammer Sledge Hammer Driller

29. Engineering Demolition
• Wrecking Ball Method
• Pusher Arm technique
• Thermic Lance Technique
• Non – Explosive Demolition
• Concrete Sawing Method
• Deliberate Collapse Method
• Pressure Jetting

30. Wrecking Ball Method
• A Steel ball anti spin device which is
suspended by a steel rope and swung by a
drag rope, the weight of the ball is around 500
to 1000 Kg used with suitable fittings attached
to a crane of adequate capacity, the building is
dismantled by making the steel ball to hit the
structure this method is much faster than
manual method

31. Wrecking Ball Method

32. Pusher Arm Technique:
• A Hydraulically powered pusher arm machine
is mounted on tracked or wheeled chassis, this
method is not recommended for large
building but it is good for small masonry
structure, the building is demolished by using
the pusher arm.
•

33. Pusher Arm Technique:

34. Thermic Lace Technique
• Flame is produced by having supply with pure
oxygen with a temperature of 2500 degree
centigrade to melt the reinforcement.

35. Thermic Lace Technique

36. Non- Explosive Demolition
• A Number of holes is drilled along the desired
line of separation and are filled with slurry
which is a special material when the slurry is
filled in the holes water is poured into the
drilled holes after few hours the slurry
expands as a result cracking will appear on the
structures which help in easy demolition of
structure.

37. Concrete Sawing Method
• Using the concrete saw the structure is been
demolished which works on a high power
supply helps in destruction of structure in an
easy way.

38. Concrete Sawing Method

39. Deliberate Collapse Method
• The Collapse is usually achieved by either by
removing key structural elements (e.g. with
explosive charges) or by wire rope pulling at a
high level of overturn this method is not
suitable for pre stressed concrete structures.

40. Pressure Jetting
• The Jet heads are generally small and so
action of jet is mainly to loosen the aggregate
by washing out softer mortar (water with high
pressure).

42. Implosion
• Collapsing the structure inward, gravity makes
the structure to collapse. If the supporting
structure of a building at a certain point is
removed the building may get damaged and the
structure can be easily demolished. The
procedure is followed by analysing the blue print
of the building and the explosives is used on the
key components of the building at different level
from bottom to top i.e. from explosion should
take place from lower level internal component
then step by step to the top level by sequential
order which result in demolition of building.

44. Deconstruction Method
• A slow and careful process that is almost the
reverse process of construction. Non
Structural Method: Dismantling of doors,
windows, flooring etc.
• Structural Method: Dismantling of beams,
Columns, Floors, walls.

45. House Demolition
• Step 1: Get the building inspected.
• Step 2: Acquire the necessary permits.
• Step 3: Disconnect existing services.
• Step 4: Tear down the house.
• Step 5: Haul away the debris.
• Traditional Mechanical Demolition.
• Deconstruction.