The document discusses various types of damages that can occur in concrete structures such as aggregate expansion, corrosion of reinforcement bars, chemical damage from carbonation and chlorides, leaching, and structural defects from design or construction issues. It then describes methods to investigate existing structures including visual inspection, non-destructive tests like rebound hammer and ultrasonic pulse velocity tests, coring concrete samples, and half-cell potential testing. Maintenance and repair of damaged concrete structures is also discussed.

1. Harminder kaur taraithia
Mtech structural engineering
11904060
Retrofitting and rehabilitation of structure
Sudhir Arora
HOD (civil dept.)
Submitted to

2. DAMAGES IN CONCRETE

3. Aggregate expansion
Various types of aggregate undergo chemical reactions in concrete, leading to
damaging expansive phenomena.
Far less common are pop-outs caused by the presence of pyrite, an iron
sulfide that generates expansion by forming iron oxide and ettringite
Among the more reactive mineral
components of some aggregates
are opal, chalcedony, flint and
strained quartz. Following the alkali-silica
reaction (ASR), an expansive gel forms,
that creates extensive cracks and damage
on structural members.

4. Corrosion of reinforcement bars
The expansion of the corrosion products
(iron oxides) of carbon steel reinforcement
structures may induce mechanical
stress that can cause the formation of
cracks and disrupt the concrete structure.
If rebars have been improperly installed or have inadequate concrete cover at
surfaces exposed to the elements, oxide jacking and spalling can occur during the
structure's lifetime: flat fragments of concrete are detached from the concrete mass
as a result of the rebar's corrosion.

5. Chemical damage
Carbon dioxide from air can react with the calcium hydroxide in concrete to form calcium
carbonate. This process is called carbonation.Carbonation of concrete is a slow and continuous
process progressing from the outer surface inward, but slows down with increasing diffusion depth.
Carbonation has two effects: it increases mechanical strength of concrete, but it also
decreases alkalinity, which is essential for corrosion prevention of the reinforcement steel.[2]
Below a pH of 10, the steel's thin layer of surface passivation dissolves and corrosion is promoted.

6. Chlorides
Chlorides, particularly calcium chloride, have been used to shorten the setting
time of concrete.[5] However, calcium chloride and (to a lesser extent) sodium
chloride have been shown to leach calcium hydroxide and cause chemical
changes in Portland cement, leading to loss of strength,[6] as well as attacking
the steel reinforcement present in most concrete.
The ten-storey Queen
Elizabeth hospital in Kota
Kinabalu contained a high
percentage of chloride causing
early failure.

7. Leaching
When water flows through cracks present in concrete, water may dissolve various minerals present
in the hardened cement paste or in the aggregates, if the solution is unsaturated with respect to
them. Dissolved ions, such as calcium (Ca2+), are leached out and transported in solution some
distance.
If the physico-chemical conditions prevailing in the seeping water evolve with distance along the
water path and water becomes supersaturated with respect to certain minerals, they can further
precipitate, making calthemite deposits (predominately calcium carbonate) inside the cracks, or at
the concrete outer surface. This process can cause the self-healing of fractures in particular
conditions.

8. In such case, the
design is required to
be reviewed in detail
and remedial
measures worked out
by the design team.
Once this is done the
methods of carrying
out the remedial
measures will be
similar to those arising
out of other defects.
Structural Defects due to Design
and Detailing

9. Structural Deficiency due to Construction Defects
Defective construction
methods form the largest
segment of source of distress
to the beams. Such defects
can be broadly subdivided as
follows:
1.Defects due to the quality of raw materials.
2.Non adoption of designed concrete mix.
3.Use of defective construction plant for producing, transporting, and placing the concrete
4.Defective workmanship.
5.Inadequate quality detailing.

10. Cracks are formed in concrete due to many reasons but when these
cracks are very deep, it is unsafe to use that concrete structure.
Various reasons for cracking are improper mix design, insufficient curing,
omission of expansion and contraction joints, use of high slump concrete
mix, unsuitable sub-grade etc.
Cracking

11. Crazing also called as pattern cracking or map cracking,
is the formation of closely spaced shallow cracks in an
uneven manner.
Crazing occurs due to rapid hardening of top surface of
concrete due to high temperatures or if the mix contains
excess water content or due to insufficient curing.
Crazing
Pattern cracking can be avoided by
proper curing, by dampening the sub-
grade to resist absorption of water from
concrete, by providing protection to the
surface from rapid temperature changes.

12. Blistering is the formation of hollow bumps of different sizes on concrete surface due to
entrapped air under the finished concrete surface.
It may cause due to excessive vibration of concrete mix or presence of excess entrapped
air in mix or due to improper finishing. Excessive evaporation of water on the top surface of
concrete will also cause blistering.
Blistering
It can be prevented by using good proportion of
ingredients in concrete mix, by covering the top
surface which reduces evaporation and using
appropriate techniques for placing and finishing.

13. Delamination is also similar to blistering. In
this case also, top surface of concrete
gets separated from underlying concrete.
Hardening of top layer of concrete before
the hardening of underlying concrete will
lead to delamination.
It is because the water and air bleeding
from underlying concrete are struck
between these two surfaces, hence space
will be formed.
Delamination
Like blistering, delamination can also be
prevented by using proper finishing techniques.
It is better to start the finishing after bleeding
process has run its course.

14. Dusting, also called as chalking is the formation of fine and loose
powdered concrete on the hardened concrete by disintegration.Dusting
To avoid dusting, use low slump concrete mix to obtain hard concrete surface with good wear resistance. Use
water reducing admixtures to obtain adequate slump. It is also recommended to use better finishing techniques
and finishing should be started after removing the bleed water from concrete surface.
Presence of
excess amount of
water in
concrete
Causes bleeding
of water from
concrete
Fine particles like
cement or sand
will rise to top
•Consequent
wear causes
dust at top
surface

15. When a concrete slab is distorted
into curved shape by upward or
downward movement of edges or
corners, it is called curling.
Curling
Top surface is dried
Cooled before bottom
surface
The surface begins to
shrink Upward curling
takes place
When bottom surface is dried
and cooled due to high
moisture and temperature,
Downward curling occurs

16. Efflorescence is the formation of deposits of salts on the
concrete surface. Formed salts generally white in color.Efflorescence
It can be prevented by using clean and pure
water for mixing, using chemically ineffective
aggregates etc. And make sure that cement
should not contain alkalis more than 1% of its
weight.
It is due to the presence of soluble salts
in the water which is used in making
concrete mix.
When concrete is hardening, these
soluble salts gets lifted to the top
surface by hydro static pressure and
after complete drying salt deposits are
formed on the surface.

17. Scaling and spalling, in both the cases
concrete surface gets deteriorated and
flaking of concrete occurs.
The main cause for this type of cases is
penetration of water through concrete
surface. This makes steel gets corroded
and spalling or scaling may occurs.
Scaling and Spalling

18. Determined the structural condition,
the need for repair or maintenance
and provided an indication as to the
safety and expected remaining service
life of the structure. The testing
consisted of:
Visual
inspection
It is done to the
exterior exposed
elements
for signs of distress
, deflection or
deterioration in
structure.
Thorough
inspection
To determine the
internal condition
of structure
Structure could be
suffering distress o
the inside whilst in
good condition.
Evaluation of the Structure

19. objective of the
investigation carried out
for the building
to obtain an up to date
account of the health
condition of the structure
so that appropriate repair
measures
To assess the
existing condition
of the structural
elements
Determine the extent
of damages in
the structure
so as to undertake
remedial measures for
rehabilitation of the
structure.
Planning Lanning of
Investigation and
Methodology
Walk over survey
to gather readily
available information
about the structure in
question
careful visual
observation of typical
crack pattern and the
nature of the spalling
Selection of tests
Tests are selected on
the basis of the
requirements of the
overall objectives of the
investigation
following in-situ and
laboratory tests were
considered
Investigation of structure

20. Chemical Tests on concrete
in the laboratory
Non-Destructive Tests
Ultrasonic Pulse
Velocity Test.
Corrosion Potential
Assessment by
conducting half-cell
potential test
Drilling out
Concrete Cores
(65mm dia),
. Rebound Hammer
Test

21. An ultrasonic pulse
velocity (UPV) test is
an insitu, nondestructive te
st to check the quality
of concrete and natural
rocks.
In this test, the strength
and quality of
concrete or rock is
assessed by measuring the
velocity of an ultrasonic
pulse passing through a
concrete structure or
natural rock formation.
• The test is conducted by passing a
pulse of ultrasonic through concrete
• Higher velocities indicate good
quality and continuity of material
• Slower velocities indicate concrete
with many cracks or voids

22. Ultra sonic pulse velocity testing
It consist of travel time, T of ultrasonic
pulse of 50 to 54 kHz, produced by an
electro-acoustical transducer, held in
contact with one surface of the concrete
member under test and receiving the
same by a similar transducer in contact
with the surface at the other end.
With the path length L, and time of
travel T, the pulse velocity (V=L/T) is
calculated.

23. Rebound Hammer test
Non-destructive testing method of concrete
which provide a convenient and rapid
indication of the compressive strength of
the concrete.
. The rebound hammer is also called as
Schmidt hammer that consist of a spring
controlled mass that slides on a plunger
within a tubular housing.
Rebound hammer test method is based on the principle that the rebound of an elastic
mass depends on the hardness of the concrete surface against which the mass strikes.

24. The plunger of rebound
hammer is pressed
against the surface of
concrete
spring controlled
mass with a constant
energy is made to hit
concrete surface to
rebound back.
The extent of rebound,
which is a measure of
surface hardness, is
measured on a
graduated scale.
This measured value is
designated as Rebound
Number (rebound
index)
concrete with low
strength and low stiffness
will absorb more energy
to yield in a lower
rebound value.

25. The half-cell potential test is the only corrosion monitoring technique
standardized by ASTM. It is used to determine the probability of corrosion
within the rebar in reinforced concrete structures.
Half cell potential test

26. It represents a cell
where each side is
referred to as a
half-cell.
Each half-cell is
represented by an
electrode in a solution
(electrolyte) and both
half-cells are
connected together.
Since one of the electrodes
has a higher tendency to
corrode compared to the
other, that electrode
(anode) will oxidize and in
turn will donate electrons.
To keep the system in
equilibrium and balance the
charges in the electrolytes,
there will be an exchange of
ions through the salt bridge.
The voltmeter will measure
the potential difference
(voltage) between both
electrodes, which indicates
the rate of dissolution of the
anode.

27. Concrete cores are usually cut by means of a rotary cutting
tool with diamond bits. In this manner, a cylindrical specimen
is obtained usually with its ends being uneven, parallel and
square and sometimes with embedded pieces of
reinforcement.
The cores are visually described and photographed, giving
specific attention to compaction, distribution of aggregates,
presence of steel etc.
Core cutter method

28. Carbonation and pH
value for concrete
The relative humidity has been shown as a deciding factor of
carbonation rate, which is at a maximum within range
between 50% and 70% of relative humidity.
Ca (OH) 2 + CO2 – CaCO3 + H2O
involve a physiochemical reaction
between atmospheric CO2 and Ca
(OH) 2 generated in cement
hydration
Step1: H20+ CO2 – (HCO3) – + H +
HCO3 - CO3 2- + H+
Step2: Ca (OH) 2 + 2H + + CO3 2- –
CaCO3 + 2H2O
The neutralization penetrates
gradually into concrete surface.
The atmospheric CO2 diffuses into
hardened concrete through pores
and when carbonation takes, the
alkanity of concrete reduces from
10 to below 9.
Carbonation test is done to
establish whether there is
sufficient thickness of un-
carbonated concrete to protect
the reinforcement for the
reminder of design life of the
structure.
even if concrete is carbonated
deeper than the reinforcement,
the reinforcement will only
corrode if there is enough
moisture in the concrete.

29. Observe the color and the depth up to
which no color is marked, and note it
down. This depth is carbonation dept.
Spray the
Phenolphthalein
indicator on the
exposed drilled
surface of
concrete
Drill the
concrete block
using a drilling
machine
Pour
phenolphthalein
indicator
solutions in 1%
quantity into
spray bottle
Carbonation test

30. This test method covers determination
of the strain of the embedment RCC
column. The subject evaluation is
focused on determining change in strain
of RCC column before load removal and
after load removal.
STRAIN GAUGE TESTS
Summary of Method: Strain is
used in converting the strain
into stress occurring in column
at different loading positions
Strain
gauge test
to determine where
the column has
released specified level
of strain after load
removal or not
Column has
tension and
moment force
resistance
capacity
Behavior of
column
under axial
loading

31. Modern concrete is a very durable
construction material and, if properly
proportioned and placed, will give
very long service under normal
conditions.
Maintenance of concrete
Many concrete structures, however,
were constructed using early concrete
technology, and they have already
provided well over 50 years of service
under harsh conditions.
Such concrete must
be inspected
regularly to ensure
that it is receiving
the maintenance
necessary to retain
serviceability.

32. How to Investigate and diagnose cracks?
appearance of cracks in RCC
structural members, it is
necessary to diagnose the root
cause
the cracks in concrete have occurred due to
corrosion of steel, further field investigation
and testing are required such as destructive
(core testing) and non-destructive testing
(Rebound Hammer, Ultrasonic pulse velocity
method and rebar location etc.).
Determine the condition of concrete i.e.
porosity, segregation, and thickness and
condition of cover.
Specify the extent of damage to the
reinforcement bars.

33. Procedure
Wrong or ineffective repair
or construction
procedures, coupled with
poor workmanship, lead to
inferior repairs. Repairs
made on new or old
concrete should be made
as soon as possible after
such need is realized and
evaluated.
Materials.—​Materials to be used in
concrete repair must be high quality,
relatively fresh, and capable of meeting
specifications requirements for the
particular application or intended use.
Mill reports or testing laboratory reports
should be required of the supplier or
manufacturer as an indication of quality
and suitability.
Workmanship
​It is the obligation of the
construction contractor or
operation and maintenance
crew to repair imperfections
or damage in concrete so that
repairs will be maintenance of
the necessary standards of
workmanship.
Well trained, competent
workmen are particularly
essential when epoxy,
polyurethane, or other resinous
materials are used in repair of
concrete.

34. The durability of the concrete can also be increased particularly on the surface by
applications of different materials which make it waterproof, hardened and resistant to
chemical attack.
Surface Treatment to Concrete
Sodium
silicate,
magnesium
or zinc
fluoride
Drying oils
like Tung or
Linseed oil
Chlorinated
rubber
paints and
neoprene
paints
Epoxy
paints
Silicon
Fluoride
treatment

36. Joint sealants should
ensure structural integrity
and serviceability.
Sealants
In the case of repair of a
cracked surface, the cracks
are first enlarged along their
exposed face and are
pointed up with the
sealants.

37. Epoxy resin systems find application in civil engineering works such as grouting of
cracks, repairs of eroded concrete structures, emergency repairs of bridges, aqueducts,
chemically corroded columns and beams.
Epoxy Resins for Concrete Repair
The chemical reaction begins as soon as the resin and hardener are combined. Most
combinations have a pot-life between 30 and 60 minutes. They develop excellent
strength and adhesive properties and are resistant to many chemicals besides
possessing good water proofing.

38. Locating the
cracks
Cleaning of the cracked
surface
Drilling and fixing of
nozzles for grouting at
suitable intervals with
epoxy putty
Grouting of epoxy
mixture with the help of
the grout pump
Sealing of nozzles
through which grouting
is done
A pre-mixed resin + hardener
is filled in the grouting vessel
and through the nozzle the
activated resin is pumped in
the cracks.
When cracks get filled
in, the grouting is
carried in the next
nozzle and so on till all
the cracks are filled in.
When cured, the epoxy
resin improves the load
carrying capacity of the
cracked structure.
Procedure of epoxy resin grouting

39. Repair Operation Material Comments
Sealing of fine cracks Epoxy resins
– Good bonding properties
even in the presence of
moisture
Sealing of large cracks and
joints
Portland cement Mortar
Polymer mortar
Putties and caulks
– Well – compacted
– Good bonding properties
– Based on synthetic
polymers and tars
General sealing of surface
Synthetic polymers and
asphalt coatings
Localized patching of
surfaces
– Concrete or mortar using
Portland cement
– Rapid-setting cements
– Polymer resins; epoxies;
polyesters
– Calcium aluminate and
regulated-set cements
– Good bonding
Overlays and shotcrete
– Portland cement concrete
– Steel fiber reinforced
concrete
– Latex modified concrete
– Polymer concrete
– Asphaltic concrete
– Quick-setting admixtures
– Resistance to cracking
– Good bonding

40. Shot Crete, gunite or sprayed
concrete is concrete or mortar conv
eyed through a hose
and pneumatically projected at
high velocity onto a surface, as a
construction technique, first used in
1914.[1]:7 It is typically reinforced by
conventional steel rods, steel mesh,
or fibers.
Shot Crete is usually an all-inclusive term for both the
wet-mix and dry-mix versions. In pool construction,
however, shotcrete refers to wet mix and gunite to dry
mix. In this context, these terms are not
interchangeable.

41. Polymer concrete composites are
relatively new developments and
have been used in structural
applications since 1950.
They possess very high strengths and are more
durable and resistant to most chemicals and acids.
PIC
polymer
impregnated
concretes
PC
polymer
concretes
PCC or
PMC
polymer cement
concretes or
polymer modified
concretes
Polymer Concrete Composites

42. Grouting
Grout is generally a mixture of water, cement, and sand and is employed in pressure
grouting, embedding rebar in masonry walls, connecting sections of pre-cast concrete,
filling voids, and sealing joints such as those between tiles.
Unlike other structural pastes such as plaster or joint compound, correctly mixed and
applied grout forms a water resistant seal.

43. Use of small diameter steel fibers in concrete has been found to improve several
properties of concrete and particularly its tensile strength and impact and wear
resistance. One of the uses of steel fiber reinforced concrete (SFRC) is in the area of
repairs and restoration of concrete structures.
The damaged
portions of a
concrete structure
can be removed and
can be made good
by placing of SFRC
to the sides and
bottom of damaged
structures by
guiniting or
shotcrete
techniques.
Steel Fiber Reinforced Concrete

44. The same treatment to columns up to the
height affected by aggressive environment
may also be carried out. Wherever the
reinforcements have corroded, the loose
particles shall have to be removed up to a
depth of 25 mm beyond the reinforcement
and epoxy treatment provided. Where the
depth of cracks extends beyond the
reinforcement, epoxy may be injected
for grouting the cracks.
Repairs of Columns:

45. Repairs of Corroded R.C.C. Slabs:
Protective coating of reinforcing steel
is applied to protect further corrosion
of the rods, with additional bars
welded on, if necessary.
The removed portions of the
concrete are then made good with a
new cement plaster/new
concrete/gunite layer as required to
fill the depth of removed concrete.
Prior to concreting, a
coat of epoxy
compound for bonding
new to old concrete
formulation to ensure
monolithic bond, shall
be applied.
As an alternative to new
concrete/gunite layer/cement
plaster, epoxy mortar of about 5
mm thickness can also be
applied.
Subsequently, protective
coating based, on epoxy
coal tar or pure epoxy
coating is applied to avoid
further corrosion.

46. Retrofitting of RCC structural members is carried
out to regain the strength of deteriorated structural concrete
elements and to prevent further distress in concrete. Strength
deficiency of concrete structural members can be due to poor
workmanship, design errors, and deterioration due to the
aggression of harmful agents.
When do RCC Structural Members
Need Retrofitting?
Structural cracks.
Damage to
structural members
Modification of
structural system.
Seismic damage.
Corrosion due to
penetration-
honey combs
Excessive
loading.
Errors in design
or construction

47. Retrofit Severely
Damaged
Concrete
Provide the
required supporting
system to the
structure
Remove
weak
concrete
Clean the surface
and clean the rust of
steel
Provide
required
formwork
Provide
additional steel
all around the
section
Apply rust
removers and
rust preventers
Provide a polymer
based bonding coat
between old and new
concrete
Place the concrete of
required thickness
and grade and
workability admixed
with plasticizers

48. Structure-Level Retrofit Structure-
level retrofits are commonly used to enhance
the lateral resistance of existing structures.
Such retrofits for RC buildings include steel
braces, post-tensioned cables, infill walls,
shear walls, masonry infill’s, and base
isolators.
Addition of RC Structural Walls
Adding structural walls is one of the most
common structure-level retrofitting methods
to strengthen existing structures. In order to
reduce time and cost, shotcrete or precast
panels can be used.

49. Steel Bracing Concentric or
eccentric bracing schemes can be used
in the selected bays of an RC frame to increase
the lateral resistance of the structure. The
advantage of this method is that an
intervention of the foundation may not be
required because steel bracings are usually
installed between existing members.
Column Jacketing Column
retrofitting is often critical to the seismic
performance of a structure. column jacketing
may be used to increase column shear and
flexural strength so that columns are not
damaged. Fiber reinforced polymer (FRC)
material is used for jackets when retrofitting
columns.

50. Slab-Column Connection Retrofits In slab-column connections, punching
shear failure due to the transfer of unbalanced moments is the most critical type of
structural damage. The retrofitting of slab-column connections is beneficial for the
prevention of punching shear failures and much research into retrofitting slab-column
connections has been conducted and reported that adding concrete capitals or steel
plates on both sides strength to self-weight ratio and do not corrode.