The document provides an introduction to the repair and rehabilitation of structures. It discusses factors contributing to damages in buildings from construction through use. Common causes of distress in concrete structures are then outlined, including construction errors, environmental factors, and chemical reactions. The objectives of conducting a condition survey of a distressed structure are presented, including identifying causes and assessing the extent of damage. The stages of a condition survey are described, beginning with a preliminary inspection, planning, visual inspection, and potentially field and laboratory testing. Classification of damage into different classes is also covered to help assess repair needs.

1. INTRODUCTION TO
REPAIR AND
REHABILITATION OF
STRUCTURES
Prepared By:
Assistant Professor Ankit Patel

2.  Since 1950s, the construction activity in India has been
increasing geometrically without matching increase in the
availability of quality inputs, in terms of materials and skilled
workmen. The gap between the quality planned and the quality
achieved continues to become wider. The factors contributing
to damages/distresses in buildings have, thus, become intrinsic
right from the construction stage. Construction documents
contain adequate specifications and instructions required to
execute quality works. However, they remain as written
document without achieving the desired level of results,
because of lack of understanding of their significance by the
field engineers. Standard cube test results are taken as a
measure of quality in the construction.
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3.  Whereas the factors such as method of placing, compaction and
curing of concrete, which have significant influence on the
quality achieved in the hardened concrete, are given scant
attention. Many a times, the quality of concrete as placed and
hardened in position has no correlation to the cube test results,
which are used for quality control measures. Procedures,
mandatory or otherwise, for periodic inspection of buildings
and documenting defects in logical manner, and recording of
structural repairs already carried out, are generally not followed
or maintained.
 The word ‘repair’ normally conveys small and ordinary repairs,
which are not of structural significance. But the aim of
rehabilitation is to restore a distressed structure back to its
original durability.
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4. Repair, Rehabilitation and Maintenance
• Repair: Repair is the process of restoring something is
damaged or deteriorated or broken, to good condition.
• Rehabilitation: Rehabilitation is the process of returning a
building or an area to its previous good conditions.
• Maintenance: Maintenance is the act of keeping something in
good condition by checking or repairing it regularly.
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5. CHAPTER-1 REPAIR
STRATEGIES
Prepared By:
Assistant Professor Ankit Patel

6. Distress In Structures:
Distress in Structure: Damage in Structure
Concrete may suffer distress or damage during its life period due
to number of reasons. Because of varying conditions under which
it is produced at various locations, the quality of concrete suffers
occasionally either during production or during service conditions
resulting in distress.
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7. Causes of Distress(Damage) in Concrete
• Structural causes ie (Externally applied loads, Environmental
loads, Accidents)
• Construction Errors & Design Errors
• Poor Construction Practices
• Construction Overloads
• Drying Shrinkage
• Thermal Stress
• Chemical Reactions
• Weathering
• Corrosion
• Acid attack
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8. Causes of Distress(Damage) in Concrete
For Plastic Concrete Distress:
Plastic Shrinkage
Early Removal Formwork
Improper design of formwork
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9. Defects, Causes, & Precautions
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10. Defects, Causes, & Precautions
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11. Causes of Distress(Damage) in Concrete
Voids in concrete
Rust Stain
Drying Shrinkage
Plastic Shrinkage
scaling
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12. Blow holes in concrete
Blow holes are individual, generally rounded, cavities on vertical surfaces of
concrete, generally less than 10 mm across. They are caused by air in the
concrete being trapped against the form face, sometimes due to insufficient
vibration. Some blow holes are almost inevitable unless a permeable formwork
material is used. The occurrence of blow holes can be minimized by the use of a
suitable release agent on the surface of the formwork and the use of adequate
vibration. In addition the concrete should have adequate workability. Blow holes
are a cosmetic problem only and will not affect the long-term performance of the
concrete structure
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13. Plucked Surface in concrete
• This appears as surface material lost upon striking the formwork
• Normally occurs when the concrete surface is not of sufficient strength when
striking the formwork. Could be due to cold weather, retarded surface, high
cement replacement or a combination thereof.
• Allowing the concrete to gain sufficient strength reduces the risk of its
occurrence and is generally accepted as being 5MPa.
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14. Distress(Damage) in Concrete
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15. Construction Errors and Design Deficiencies:
Poor construction practices and negligence can cause defects that lead to the
cracking and concrete deterioration. These include:
 Scaling, Dusting of concrete
 Improper alignment of formwork
 Movement of formwork
 Improper location of reinforcing steel
 Improper curing
Errors made during construction such as adding improper amounts of water to
the concrete mix, improper curing cause distress and deterioration of the
concrete. Proper mix design , placement and curing of the concrete, as well as
an experienced contractor are essential to prevent constructing errors from
occurring. Construction errors can lead to some of the problem such as scaling
and cracking. Honeycombing and bug holes can be observed after
construction. Honeycombing can be recognized by expose coarse aggregate on
the surface without any mortar covering or surrounding the aggregate particles.
The honeycombing may extend deep into the concrete. Honeycombing can be
caused by a poorly graded concrete mix, by too large of aggregates, or
insufficient vibration at the time of placement .
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16. Construction Errors and Design Deficiencies:
Bug holes is the term used to describe small holes that are noticeable on the
surface of the concrete. Bug holes are generally caused by too much sand in a
mix, a mix that is too lean or excessive amplitude of vibration during placement.
Bug holes may cause durability problems with the concrete should be monitors.
Design Errors:
It is broadly divided into two parts
1. Inadequate structural design:
The failure mechanism is due to over stressing of concrete beyond its capacity.
These defects will me manifested in the concrete either by cracking or spalling. If
the concrete experience high compressive stresses then spalling will occur. If
concrete expose to high torsional or shearing stresses then spalling or cracking
may occur and high tensile stresses will cause the concrete to crack. Such defects
will be present in the areas where high stresses are expected. Through visual
inspection engineer should decide weather to proceed for detail analysis. These
problems can be prevented with a careful review of design calculations and
detailing.
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17. Construction Errors and Design Deficiencies:
2. Poor Design Detail:
An adequate design does not guarantee a satisfactory function without
including design detailing. Detailing is an important component of
structural design. Poor detailing may or may not directly lead to a
structural failure but it may contribute to the deterioration of the concrete.
In order to fix a detailing defect it is necessary to correct the detailing and
not to respond to the symptoms only. Some of the design and detailing
defects include:
1. Abrupt Changes in the section
2. Insufficient reinforcement at corners and openings
3. Inadequate provision of drainage
4. Inadequate expansion joint
5. Material incompatibility
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18. Condition Survey
Condition Survey is an examination of concrete for the purpose of
identifying and defining area of distress. While it is referred in
connection with survey of concrete and embedded reinforcement that is
showing some degree of distress, its application is recommended for all
buildings and structures. The system is designed to be used for recording
the history of the project from its inception to completion and
subsequent life.
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19. Objectives of Condition Survey
• The objective of Condition Survey of a building structure is
• To identify Causes of distress and Their sources;
• To assess The extent of distress occurred due to corrosion, fire,
earthquake or anyother reason, The residual strength of the structure
and Its rehabilitability;
• To prioritise the distressed elements according to seriousness for
repairs and
• To select and plan the effective remedy.
• “Find the cause, the remedy will suggest itself”. Sometimes, the
source of the cause of distress is different than what is apparently
seen. It is, therefore, essential that the engineers conducting condition
survey determine the source(s) of cause so as to effectively deal with
it and minimize their effects by proper treatment.
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20. Stages of Condition Survey
Stages for carrying out Condition Survey largely depend on field
conditions, user habits, maintenance, etc. Condition Survey of a
building/structure is generally undertaken in four different stages to
identify the actual problem so as to ensure that a fruitful outcome is
achieved with minimum efforts & at the least cost. The four stages of
Condition Survey described are:
Preliminary Inspection,
Planning,
Visual Inspection,
Field and Laboratory testing
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21. 1. Preliminary Inspection
A.The primary objective of the preliminary inspection is:
1. To assess and collect following necessary information for a thoughtful
planning before a condition survey is physically undertaken:
 Background history of the distressed structure From the
Owners/Clients From the occupants of building, general public, etc
based on personal enquiries;
 Notes and records of earlier repairs, if carried out,
 All possible relevant data and information;
 The safety requirements for condition survey team;
 Necessary site preparations including access scaffolds, working
platforms, etc, if any;
 The approx. time required for survey;BITS Edu Campus
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22. 1. Preliminary Inspection
 The extent and quantum of survey work;
 The requirement of field-testing equipment's, Tools for sampling.
2. To advise the client/owner of the building in regard to take immediate
safety measures.
3. To define the scope of work of field investigations with the
Clients/Owners.
B. Basic Information Gathering: A programme has to be evolved to
obtain as much information as possible about the distressed structure at
reasonable cost and in a reasonable time. Accordingly, the information
required from the owner/client has to be listed out. Even though; many
construction details and other related information may not be available
with the owners/clients, yet as much as information and details as
possible be gathered during the Preliminary Site Visit. Before
undertaking a Condition Survey of a building/structure, the following
essential information is required and be obtained from the clients/owners:
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23. 1. Preliminary Inspection
 Period of construction;
 Construction details including architectural, structural and as built
drawings;
 Exposure conditions of structure;
 Present use of structure;
 Previous changes in use, if any;
 Record of structural changes made, if any;
 Record of first occurrence of deterioration, if any;
 Details of repairs, if carried out in the past;
 Reports of previous investigations/condition surveys, if any;
 Photographs of distressed portions of structure.BITS Edu Campus
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24. 1. Preliminary Inspection
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25. 1. Preliminary Inspection
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26. 1. Preliminary Inspection
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27. 1. Preliminary Inspection
C. Photographic Record: It is always necessary to carry a camera with
flash during such ‘Preliminary inspection’ and take necessary photographs
of the distressed structure and its members. Preliminary Inspection and
collection of data would be helpful in planning, the Condition Survey for
field investigations. This allows a reasonably sufficient understanding of
the cause of distress for an experienced Rehabilitation Engineer.
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28. General approach for pre-repair
evaluation of distress concrete
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29. 2. Planning Stage
Planning stage involves preparation of field documents, grouping of
structural members and classification of damage as under:
• Preparation of Field Documents:
• For condition survey, the following are required to be prepared:
 Survey objective;
 Scope of work;
 Method of survey;
 The field and laboratory testing requirements and field
equipment's & tools required for the same;
 Maintenance and repair records.
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30. 2. Planning Stage
 Required number of photo copy of available drawings;
 Floor plans based on field measurements;
 Work sheets and tables for recording in a logical manner all
information, test results including field data gathered;
 Previous Condition Survey results and Investigation Reports, if
any;
 Maintenance and repair records.
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31. 2. Planning Stage
Grouping of the Structural members:
Soon after the preliminary site visit and on obtaining of building plans,
the structural members shall be grouped as per their type and based on
similarity of exposure conditions for proper appreciation of the cause of
distress. For example in a building subjected to normal environmental
attack, the grouping could be done as under:
 External columns/beams would be subjected to more severe
environmental attack than the internal structural members of a
building and could be grouped in two broad groups.
 Even from amongst the external columns, those at corners or projected
out are likely to be exposed more due to adjacent faces being exposed
than those not at corners or un-projected columns. Hence to be
grouped separately.BITS Edu Campus
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32. 2. Planning Stage
 The members subjected to dampness/wetting/drying located in or
around the toilet shafts are likely to undergo similar class of distress
and be grouped separately.
 Structural members with different protective finishes have to be
grouped separately.
• Classification of Damage:
• Based on the preliminary data collected and site visit, the
rehabilitation engineer should interpret rules and subdivide the repair
classification broadly in to five classes as ‘Class 0’ to ‘Class 4’ named
as Cosmetic Repair, Superficial Repair, Patch, Repair, Principal
Repair and Major Repair.
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33. Classification of Damage
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34. Classification of Damage
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35. 3. Visual Inspection
1. Visual Inspection and observations:
Visual examination of a structure is the most effective qualitative
method of evaluation of structural soundness and identifying the
typical distress symptoms together with the associated problems.
 This provides valuable information to an experienced engineer in
regard to its workmanship, structural serviceability and material
deterioration mechanism.
 It is meant to give a quick scan of the structure to assess its state
of general health.
 The record of visual inspection is an essential requirement for
preparation of realistic bill of quantities of various repair items.
 Experienced engineers should carry out this work as these forms
the basis for detailing out the plan of action to complete the
diagnosis of problems and to quantify the extent of distress.BITS Edu Campus
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36. 3. Visual Inspection
 Simple tools and Instruments like camera with flash, magnifying
glass, binoculars, and gauge for crack width measurement, chisel
and hammer are usually needed. Occasionally, a light
platform/scaffold tower can be used for access to advantage.
 The study of crack pattern leads to the primary cause of damage.
The mesh pattern generally suggests that the distress in a structure
could be due to drying shrinkage, frost action or alkali aggregate
reaction.
 The cracking along the reinforcement indicates that the damage
could be due to corrosion of reinforcement.
 The study of colour and texture of the concrete and condition of
fixtures is very much useful in investigation of fire damage
structure.
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37. 3. Visual Inspection
2. Questioning of personnel/Scrutiny of field data and records:
The questioning of personnel and the scrutiny of field data and records is
carried out for the following:
 Grade of concrete adopted
 Cube test results
 Type of materials and sources
 Construction details
 Environmental conditions
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38. 3. Visual Inspection
Commonly
Observed Order
Location of RCC component
Deterioration of RCC Building
First Wet / water stagnating areas with RCC elements located on external
direct exposed walls/slabs and frequented with alternate wetting/drying
cycle.
Second Thin exposed non structural RCC elements e.g. chhajjas, railings etc.
Third Terrace RCC slab with ineffective insulation, water proofing and
drainage systems
Fourth Wet areas with RCC elements located on inner unexposed walls and
frequented with alternate wetting/drying cycle
Fifth Beams/columns with one face exposed direct to sun and rain and the
other face unexposed.
Sixth Beams/Columns exposed to rain and sun from all sides.
Last Beams/Columns/Slabs located in the interior of building.
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39. 3. Visual Inspection
Types of cracks in concrete structures:
 Structural cracks.
 Non Structural 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 and their inmates.
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.
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40. 3. Visual Inspection
Defects in Concrete:
• Concrete defects can be broadly classified into two categories :
• 1. Macro Defects:
• If these defects are present, concrete has low strength and will rapidly
deteriorate due to easy ingress of water and other chemicals.
Invariably, structure will require repairs within a few years of its
construction. Causes will have to be analysed and defects removed
before doing any additional protective treatment. Often,
waterproofing of concrete slabs is carried out superficially and it fails
to give the desired benefit because the defective concrete below this
waterproofing layer has not been treated to seal the macro/micro
defects which existed within the concrete slab. The main causes of
these defects are generally due to inadequacies in design and / or
construction practices.BITS Edu Campus
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41. 3. Visual Inspection
• 2 Micro Defects:
• These defects are not visible to the naked eye. They are usually very
fine voids caused by large capillary pores resulting from the use of
low grades (strength) of concrete with high water to cement ratio.
• They could also occur due to addition of excess water or high water
to cement ratio of concrete mix. Fine cracks are generally present in
concrete and can occur due to various reasons. They do not pose a
serious threat to concrete deterioration initially as they are generally
not deep and are discontinuous. With lapse of time due to variations
in temperatures, changes in weather conditions, changes in loading
conditions they increase in depth, length and width and combine with
other fine cracks to create continuous passage for moisture, chlorides,
sulphates and other chemicals from the environment to enter and start
corrosion of steel in concrete and other deleterious reactions.BITS Edu Campus
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42. 3. Visual Inspection
To conclude, macro defects and micro defects in concrete are both
harmful to the health of buildings and can cause deterioration of
concrete depending on the extent of their presence, environmental
conditions around the building and maintenance done during its life
cycle. However macro defects by virtue of being larger can cause faster
deterioration and more damage to the structure than the micro defects
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43. 3. Visual Inspection
Obstructions to visual inspection:
 Recently done paints, patch work of replaster, false ceiling etc. are
likely to create obstructions to visual inspection. Carefully analyze
such areas
 Insufficient light inside the building.
 The access height from within and from outside during visual
inspection could also be a major problem.
Types of cracks and their pattern:
 It is generally easy to differentiate various types of cracks and relate
them with the cause of distress. The location of cracks and their
pattern give the first indication of the problem.
 Cracking and spalling, or rust staning are visual indication of the
corrosion of steel in concrete. Corrosion cracks run along the
reinforcement location.
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44. 3. Visual Inspection
 A mesh pattern of cracks suggests drying shrinkage, alkali aggregate
reaction or frost attack,
 Cracks at right angle to main reinforcement are generally associated
with structural deficiency.
 Cracking along the bar can be an important indication that the
reinforcements are subjected to corrosion.
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45. 3. Visual Inspection
.
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46. 3. Visual Inspection
Worksheet
The visual inspection shall largely cover:
• Recording of Areas of high distress;
• Cracks & their location;
• Excessive deflection;
• Exposure conditions of various distressed areas;
• Moisture, leakage/ seepage & dampness locations;
• Abnormal vibrations in structure, if any;
• Algae, fungus growth and/or efflorescence etc and their locations;
• Photographic records,
Visual inspection is, therefore, the best way of qualitative assessment of
any structure. BITS Edu Campus
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47. 4. Field/laboratory Testing Stage
• Objective:
 It may neither be feasible nor is the practice to conduct field/laboratory
testing on every structural member in an existing distressed building.
 The field/laboratory testing of structural concrete and reinforcement is to
be undertaken, basically for validating the findings of visual inspection.
 These may be undertaken on selective basis on representative structural
members from each of the various groups based on exposure conditions
as explained in the preceding sections.
 The programme of such testing has to be chalked out based on the record
of visual inspection.
 After identification of weak zones in a structure, detailed assessment of
insitu quality of material is done. A number of test have been developed
for different properties of concrete.
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48. Considerations for Repair Strategy
In the Condition Survey Report, before arriving at the Repair Strategy, it
shall include the following considerations:
 Identification of the cause of problem and its source is the fundamental
to the success or failure of the repair. A lack of attention at this point can
put at risk the whole job.
 For arriving at an effective and economical solution, systematic
documentation of all observations is essential.
 Available space and accessibility will determine the selection of repair
method and repair strategy.
 Depending upon the scope and scale of repairs, the repair strategy has to
suit the on-going activities in the building.
 The prioritization of repairs and their sequencing are important
components for deciding the repair strategy.
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49. Considerations for Repair Strategy
 Major repair procedure may demand propping the structural members to
relieve a part or full component of the load acting on the member. If the
building requires extensive propping, vacating the building may become
the pre-requisite.
 Safety measures to prevent any immediate major mishap shall be
prescribed without loosing further time.
 The report should also include requirements on safety measures to be
adopted during execution of repair jobs.
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50. NON DESTRUCTIVE EVALUATION
TESTSA number of non-destructive evaluation (NDE) tests for concrete
members are available to determine in-situ strength and quality of
concrete. Some of these tests are very useful in assessment of damage to
RCC structures subjected to corrosion, chemical attack, and fire and due
to other reasons. The term ‘non destructive’ is used to indicate that it
does not impair the intended performance of the structural member
being tested/investigated. The non-destructive evaluation has been
broadly classified under two broad categories via ‘in-situ field test’ and
‘laboratory test’. These tests have been put under four categories
depending on the purpose of test as under:
 In-situ Concrete Strength
 Chemical Attack
 Corrosion Activity
 Fire DamageBITS Edu Campus
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51. Concrete Strength Assessment
A. Objective:
 Generally, in-situ non-destructive evaluation of concrete is to have an
overall idea of the quality of concrete.
 In some cases, a sufficiently accurate estimate of quantitative value of
concrete strength is required for assessment of load carrying capacity of
a structural member. The need for such an estimate may arise during
evaluation of change in usage of structure, modification or extension of
the original structure or damage due to fire, earthquake, etc
B. Limitations:
 The accuracy is not very high as most of the non-destructive methods of
evaluation of concrete strength are based on indirect measurement of
concrete strength.
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52. Rebound Hammer Test
 The operation of Rebound Hammer (also called Schmidt’s Hammer)
is illustrated in Figure When the plunger of rebound hammer is
pressed against the surface of concrete, a spring controlled mass with
a constant energy is made to hit concrete surface to rebound back.
This test is conducted to assess the relative strength of concrete based
on the hardness at or near its exposed surface and to identify relative
surface weaknesses in cover concrete and also can be used to
determine the relative compressive strength of concrete. Locations
possessing very low rebound numbers will be identified as weak
surface concrete and such locations will be identified for further
investigations like corrosion distress, fire damage and/or any other
reason including original construction defects of concrete. 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 (a rebound index). A concrete with low strength and low
stiffness will absorb more energy to yield in a lower rebound value.
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53. Rebound Hammer Test
• The results are significantly affected by the following factors:
 a. Mix characteristics:
 i. Cement type,
 ii. Cement Content,
 iii. Course aggregate type:
 b. Angle of Inclination of direction of hammer with reference to
horizontal
 c. Member Characteristics,
 ii. Compaction,
 iii. Surface type,
 iv. Age, rate of hardening and curing type,
 v. Surface carbonation,
 vi. Moisture Condition,
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54. Rebound Hammer Test
Average Rebound Quality of Concrete
>40 Very Good
30-40 Good
20-30 Fair
<20 Poor and/or delaminated
0 Very Poor and/or delaminated
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55. Rebound Hammer Test
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56. Ultrasonic Pulse Velocity Test
 The ultrasonic pulse velocity method basically involves the
measurement of velocity electronics pulses passing through concrete
from a transmitting transducer to a receiving transducer. The density
and elastic properties are in turn related to the quality and the
strength of material. The pulse velocities ranges from about 3 to 5
km/s.
 An Ultrasonic pulse apparatus consists of a transmitter and a receiver
which are held again two faces of concrete. The apparatus generates
pulses of ultrasonic frequency which are transmitted through
concrete by the transmitter. On the other face, the receiver receives
the pulses and the apparatus records them. The time of travel
between initial onset and the reception of the pulse is measured
electronically. The path length between the transducer and the
receiver, divided by the time of travel gives the average velocity of
wave propagation. The velocity of pulses is correlated to the strength
of concrete. Higher the velocity of pulses greater the strength of
concrete.
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57. Ultrasonic Pulse Velocity Test
Pulse Velocity Concrete quality
> 4.0 km/s Very good to excellent
3.5-4.0 km/s Good to very good, slight porosity may exist.
3.0- 3.5 km/s Satisfactory but loss of integrity is suspected
<3.0 km/s Poor and loss of integrity exist
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58. Penetration Resistance (‘Windsor Probe’
and ‘PNR Tester’)
 The determination of the resistance of concrete to penetration by a steel
rode or probe, driven by a fixed amount of energy can be assess the
compressive strength of concrete. The Principal is that, the depth of
penetration is inversely proportional to the compressive strength. The
relation between strength of concrete and the depth of penetration
greatly depends on the hardness of the aggregate because the coarse
aggregate particles become fractured in the penetration tests.
 This technique offers a means of determining relative strengths of
concrete in the same structure or relative strength of different structures.
Because of the nature of equipment, it can not, and should not be
expected to yield absolute values of strength. ‘Windsor Probe’, as
commercially known, is penetration resistance measurement equipment,
which consists of a gun powder actuated driver, hardened alloy rod
probe, loaded cartridges, a depth gauge and other related accessories.BITS Edu Campus
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59. Penetration Resistance (‘Windsor Probe’
and ‘PNR Tester’)
 In this technique, a gunpowder-actuated drivers used to fire a
hardened alloy probe into the concrete. During testing, it is the
exposed length of probe, which is measured by a calibration depth
gauge.. Being a low energy device, sensitivity is reduced at higher
strengths. Hence, it is not recommended for testing concrete having
strength above 28 N/sqmm. The penetration of pin creates a small
indentation (or hole) on the surface of concrete. The pin is removed
from the hole, the hole is cleaned with an air jet and the whole depth
is measured with a suitable depth gauge. Each time a new pin is
required as the pin gets blunted after use. The strength properties of
both mortar and stone aggregate influence the penetration depth of
the probe in a concrete. It is claimed an average coefficient of
variation for a series of groups of three readings on similar concrete
of the order of 4% may be expected.BITS Edu Campus
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60. Penetration Resistance (‘Windsor Probe’
and ‘PNR Tester’)
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61. Pull out Testing
As the name suggests, this method involves the measurement of the
force required to pull out a specially shaped steel rod or some similar
device from a concrete surface. There two basic categories one which
involves an insert having to be cast into the concrete is called cast-in
method and another where the insert is fixed into a hole drilling into
hardened concrete is called drilled hole method and it is more
appropriate for field survey of hardened concrete.
1. Cast-in Method (LOK Test):
The main aim of this technique is to measure the tensile force required
to pull-out the a metal insert which has been cast into the fresh concrete.
This test is commercially known as LOK-test. In this system the insert is
directly attached to the formwork. The basic geometry of insert contains
25mm diameter disc attach to a removable steam which locates the disc
25mm below the concrete surface. To prevent the disc rotating when the
stem is being removed a 15mm notch is provided on one side of the
disc.
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62. Pull out Testing
The load is applied to the disc through a removable pull-bolt using a
hydraulic jack which has a constant loading rate. From the peak tensile load
recorded by the jack the cube compressive strength is estimated.
2. Drilled-hole method (CAPO Test):
It is observed that one of the main limitations of the cast-in method was
that the inserts needed to be place before or at least during concreting
process. To overcome this problem another type of pull out test was
developed which would be completed on existing structures. The basic
geometry of this is same as the cast-in method. The main advantage of this
method is extremely valuable for in situ strength assessment. The CAPO is
based on the expression cut and pull out. The basic procedure for this test
consists of drilling a 45mm deep, 18mm dia hole after which a 25mm dia
groove is cut at a depth of 25mm using portable reaming machine.
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63. Pull out Testing
An expanding ring is than placed and expanded into grove using a pull bolt
assembly. The convenient LOK Test pulling equipment is then attach to the
pull bolt continues until the cone of concrete is removed to allow retrieval
of the pull bolt.
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64. Chemical Test
Some of the chemical test are as follows:
 Depth of carbonation
 Chloride content
 Cement content
 Sulphate content
 Alkali content
1. Depth of carbonation:
This test is carried out to determine the depth of concrete affected due to
combines attack of atmospheric carbon dioxide and moisture causing g
a reduction level of alkanity of concrete.
A spray of 0.2% solution of phenolphthalein is used as pH indicator of
concrete. The change of color of concrete to pink indicates that the
concrete is in a good health, where no change in color takes place, it is
suggestive of carbonation affected concrete.
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65. Chemical Test
The i-situ test is conducted by drilling a hole on the concrete surface
upto cover concrete thickness, removing dust by air blowing spraying
0.2% solution of phenolphthalein with physician’s injection syringe and
needle on such freshly drilled concrete and observing the color change.
2. Chloride content:
It is important to know the level of chloride near the steel concrete
interface. Chloride present in concrete are fixed as well as free. Though
it is free chloride ions which are importance from corrosion risk point of
view. Chloride contents are determined and compared with the limiting
values specified for the concrete to assess the rise of corrosion in
concrete.
As per IS code the test consists of obtaining powdered samples by
drilling and collecting from different depths ie 5mm and mixing the
sample with a special chloride extraction liquid and measuring the
electrical potential of the liquid by chloride ion sensitive electrode.
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66. Corrosion Assessment (test)
1. Cover meter survey:
The main purpose of providing concrete cover to reinforcement is to
protect it from corrosion. A Cover thickness survey is useful to
determine existing cover thickness in a specific location where a
damage has been identified and elsewhere for comparison on same
structure. A cover meter is use to measure the thickness of cover, dia of
rebar and spacing of rebars.
2. Half cell potential survey:
The corrosion of steel in concrete is an electrochemical process.
Depending on the corrosion activity the electrode potential of steel rebar
undergoes changes with reference to a standard electrode. By making
measurements on well defined grid points over the whole surface, a
distinction can be made between corroding and non-corroding locations.
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67. Corrosion Assessment (test)
The various standard electrodes used are:
Copper-copper sulphate electrode
Silver-silver chloride electrode
A reference electrode is connected to the rebar and voltage difference is
measured between the rebar and the reference electrode. Generally, the
voltage potential becomes more and more negative as the corrosion
becomes more and more active.
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68. Fire Damage Assessment
The current practice is to assess fire rating of building rather than fire
resistance of materials although fire resistance has a significant
contribution to fire rating.
Generally fire resistance of a material or fire rating of an element
depends on:
 Properties of materials
 Temperatures generated during fire
 Duration of fire exposure
Concrete can resist fire up to about 200-300 degree Celsius. It is non
combustible material and does not give out smoke or fumes when
expose to fire.
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69. Fire Damage Assessment
The factor affecting the fire resistance of concrete are:
1. Type of aggregate: Igneous stone aggregate will be more stable
against fire. Light weight aggregates offer vary good fire resistance.
2. Lean Concrete: Lean concrete having low cement content show
better resistance to fire.
3. Admixtures: Concrete with admixtures like fly ash, ground furnace
slag also have better fire resistance.
4. Moisture content in concrete: Moist concrete disintegrates faster
than dry concrete.
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70. Fire Damage Assessment
DTA- Differential Thermal Analysis:
This technique is use to study the physical and chemical changes that
occur in a material when it is heated. It is concerned with the rate of
change of temperature of a sample as it is heated at a constant rate of
heat flow. Its principle is based on “when a material is slowly heated its
temperature rises but when the material undergoes any endothermic
reaction ie losing water, losing carbon dioxide its temperature remains
constant.” In DTA study the sample and an inert material are heated
separately and the difference of temp between the two is recorded by
means of thermocouples which generated an electrical signal whenever
there is temp differences between the reference and the sample. When
there is no endothermic reaction in the sample there would not be any
differences of temp between the reference and the sample and hence no
electrical signal would occur.
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71. Fire Damage Assessment
The results of DTA are presented in the form of DTA curves. The
occurrence of any pulse appears as a peak in the DTA curve which is a
plot of temp versus electrical signal generated. Qualitative composition
of the sample can be judged by measuring the size of the peak in the
DTA curve. The peak size is directly related with the amount of heat
involved in the transition.
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72. THANKYOU
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Prof. Ankit Patel