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Module 2

Damage diagnosis and assessment - Various aspects of Inspection, Assessment

procedure for
evaluating a damaged structure, Visual inspection, Non Destructive Testing using
Rebound hammer, Ultra sonic pulse velocity, Semi destructive testing, Probe test, Pull
out test, Chloride penetration test, Carbonation, Carbonation depth testing, Corrosion
activity measurement, Core test, Load test.

Various aspects of Inspection

inspection is the process of careful examination to understand the defects or problems.

There are four types of inspection for reinforced concrete structure namely:

Types of Reinforced Concrete Structure Inspections

1. Inventory Inspection
Inventory inspection is carried out when the construction of a structure is ended and it
becomes ready to be delivered, when a change in configuration is applied, or when a
structure is ready back to service after a major intervention. The results of inventory
inspection is used as a baseline for other inspections that may be conducted in the future.

2. Routine Inspection
Routine inspection is the periodic and quick examination of the general conditions of
concrete structure which is carried out by competent and qualified engineers.

Each inspection should be recorded accurately and properly. Primarily, the inspector
carries out visual assessment, and may employ simple instrumental aids to specify the
condition of the concrete structure.

The principal purpose of routine inspection is to discover all indications of deterioration

or damage such as texture or color of concrete, exudation, cracks, spalling, delamination,
leaching, rust streaks, deformation, loss of camber, and salt build-up.
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3. Detailed Inspection
Detailed or comprehensive inspection is a more intensive, time consuming, and thorough
inspection than the routine inspection. It is performed between certain number of routine
inspection and is scheduled based on the importance of the structure.

The inspector should closely examine all the details of the structure such as structural,
mechanical, environmental, durability, material, and electrical details.

If necessary, specialized tools, such as hammer sound testing or any other non-destructive
test, would be used to accurately determine the state of the structure. The detailed
inspection should be carried out by specially trained engineers who can plan
comprehensive repairs.

4. Special Inspection
Special inspection of concrete structures is done in special conditions after the occurrence
of unusual events. So, special inspection is need-based and is carried out as and when
required. Special inspection may require supplementary testing and structural
analysis and may require detailed involvement of a structural engineer.

The outcomes of this type of inspection should be enough to make a proper decision
about the next action to be undertaken for the structure under considerations. Conditions
in which special inspection is required may include but not limited to the following
circumstances:

 When signs of weaknesses discovered during routine or detailed inspection or by

any other observation.
 When the structure loading is to be increased due to revised or increased loading
standard.
 Distressed concrete structures.
 When subsidence occurs in areas of mineral or coal extraction.
 When settlement of foundation takes place.
 When seismic activity takes place.
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 In case of exceptional events for example flood, storm, fire, accidents, etc.

Assessment procedure for evaluating a damaged structure

For assessment of damage of a structure the following general considerations have to be

take account.

1) Physical inspection of damaged structure. –visual inspection

2) Presentation and documenting the damage.

3) Collection of samples and carrying out tests both in situ and in lab.

4) Studying the documents including structural aspects.

5) Estimation of loads acting on the structure.

6) Estimate of environmental effects including soil structure interaction.

7) Diagnosis.

8) Taking preventive steps not to cause further damage.

9) Retrospective analysis to get the diagnosis confirmed.

10) Assessment of structural adequacy.

11) Estimation of future use.

12) Remedial measures necessary to strengthen and repairing the structure.

13) Post repair evaluation through tests.

14) Load test to study the behavior.

15) Choice of course of action for the restoration of structure.

A simple flow chart incorporating the above points is presented in fig 1.1.
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Visual inspection

Visual inspection is one of the most versatile and powerful tools to evaluate the
condition of a concrete structure. Visual inspection can provide detailed information
that may lead to positive identification of the cause of distress.

 Visual testing is the most important of all non-destructive tests.

 Extensive information can be gathered from visual inspection to give a
preliminary indication of the condition of the structure and allow formulation of a
subsequent testing programme.
 The visual inspection however should not be confined only to the structure being
investigated. It should also include neighbouring structures, the surrounding
environment and the climatic condition.
TOOLS AND EQUIPMENT FOR VISUAL INSPECTION
 common accessories such as measuring tapes or rulers, markers, thermometers,
anemometers and others. Binoculars, telescopes, borescopes and endoscopes or the
more expensive fibre scopes may be useful where access is difficult.
 A crack width microscope or a crack width gauge is useful, while a magnifying
glass or portable microscope is handy for close up examination.
 A good camera with the necessary zoom and micro lenses and other accessories,
such as polarized filters, facilitates pictorial documentation of defects,
 a portable colour chart is helpful in identifying variation in the colour of the
concrete.
 A complete set of relevant drawings showing plan views, elevations and typical
structural details allows recording of observations to be made.
GENERAL PROCEDURE
 Before visual inspection, the engineer must peruse all relevant structural drawings,
plans and elevations to become familiar with the structure. Available documents
must also be examined and these include technical specification, past reports of
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tests or inspection made, construction records, details of materials used, methods

and dates of construction, etc.
 The survey should be carried out systematically and cover the defects present, the
current and past use of the structure, the condition of adjacent structures and
environmental condition.
 All defects must be identified, the degree classified, similar to those used for fire
damaged concrete and, where possible, the causes identified.
 The distribution and extent of defects need to be clearly recognized. For example
whether the defects are random or appear in a specific pattern and whether the
defect is confined to certain locations of members or is present all over the
structure.
 Visual comparison of similar members is particularly valuable as a preliminary to
testing to determine the extent of the problems in such cases.
 A study of similar structures or other structures in the local area constructed with
similar materials can also be helpful in providing ‘case study’ evidence,
particularly if those other structures vary in age from the one under investigation.
 There is a need to identify associated or accompanying defects, especially which
particular defect predominates.
 Segregation or excessive bleeding at shutter joints may reflect problems with the
concrete mix, as might plastic shrinkage cracking, whereas honeycombing may be
an indication of a low standard of construction workmanship. Lack of structural
adequacy may show itself by excessive deflection or flexural cracking and this
may frequently be the reason for an in situ assessment of a structure.
 Long term creep defections, thermal movements or structural movements may
cause distortion of doorframes, cracking of windows, or cracking of a structure or
its finishes.
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 Material deterioration is often indicated by surface cracking and spalling of the

concrete and examination of crack patterns may provide a preliminary indication
of the cause.
 Visual inspection is not confined to the surface but may also include examination
of bearings, expansion joints, drainage channels and similar features of a structure.
 Any misuse of the structure can be identified when compared to the original
designed purpose of the structure.
 An assessment may also need to be made of the particular environmental
conditions to which each part of the structure has been exposed. In particular the
wetting and drying frequency and temperature variation that an element is
subjected to should be recorded because these factors influence various
mechanisms of deterioration in concrete. For example, in marine structures it is
important to identify the splash zone. Settlement of surrounding soil or
geotechnical failures need to be recorded.
 Account must also be taken of climatic and other external environmental factors
at the location, since factors such as freeze thaw conditions may be of considerable
importance when assessing the causes of deterioration.
 A careful and detailed record of all observations should be made as the inspection
proceeds.
 Drawings can be marked, coloured or shaded to indicate the local severity of each
feature.

Defects that commonly need recording include:

 cracking which can vary widely in nature and style depending on the causative
Mechanism
 surface pitting and spalling
 surface staining
 differential movements or displacements
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 variation in algal or vegetative growths

 surface voids
 honeycombing
 bleed marks
 constructional and lift joints
 exudation of efflorescence.

.Non Destructive Testing

Non-destructive tests of concrete is a method to obtain the properties of concrete from the
existing structures. This test provides immediate results.

Non destructive techniques can be used for the following purposes:

➢ Test on actual structures

➢ Test on various stages

➢ Assess the quality control of actual structures

➢ Assess the uniformity of concrete

➢ Assess the materials used and workmanship with specification

➢ Assess the poor construction practices

➢ Assessment of the extent of cracks, voids, honeycomb

➢ Confirmation of suspected distress due to poor design

➢ Assessment of partial durability

➢ Monitoring of progressive changes in structure

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METHODS OF NON-DESTRUCTIVE TESTING

➢ Surface Hardness Method

➢ Ultrasonic Pulse Velocity Method

➢ Resonant Frequency Method

➢ Dynamic or vibration method

➢ Pulse Attenuation Method

➢ Pulse Echo Method

➢ Radioactive Method

➢ Nuclear Methods

➢ Magnetic Methods

➢ Electro magnetic methods

➢ Electrical methods

➢ Acoustic Emission Technique

➢ Radar Technique

➢ Radiography Methods

Rebound hammer

SCHMIDT REBOUND HAMMER TEST

PRINCIPLE

This is principally a surface hardness tester. It works on the principle that the rebound of
an elastic mass depends on the hardness of the surface against which the mass
strikes.
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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.
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).

Objective
As per the Indian code IS: 13311(2)-1992, the rebound hammer test have the following
objectives:

1. To determine the compressive strength of the concrete by relating the rebound

index and the compressive strength
2. To assess the uniformity of the concrete
3. To assess the quality of the concrete based on the standard specifications
4. To relate one concrete element with other in terms of quality

PROCEDURE
The hammer weighs about 1.8 kg and is suitable for use both in a laboratory and in the
field.

 With the hammer pushed hard against the concrete.

 The plunger is then held perpendicular to the concrete surface and the body
pushed
towards the concrete.
 The mass hits the shoulder of the plunger rod and rebounds.
 During rebound the slide indicator travels with the hammer mass and stops at the
maximum distance the mass reaches after rebounding.
 A button on the side of the body is pushed to lock the plunger into the retracted
position and the rebound number is read from a scale on the body.
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APPLICATIONS OF SCHMIDT REBOUND HAMMER TEST

 The hammer can be used in the horizontal, vertically overhead or vertically
downward positions as well as at any intermediate angle, provided the hammer is
perpendicular to the surface under test.
 The position of the mass relative to the vertical, however, affects the rebound
number due to the action of gravity on the mass in the hammer. Thus the rebound
number of a floor would be expected to be smaller than that of a soffit and inclined
and vertical surfaces would yield intermediate results.
 A high rebound number represents concrete with a higher compressive strength.
 A correlation can be developed between the rebound number and concrete.
 The concrete surface should be smooth, clean and dry.

 Any loose particles should be rubbed off from the concrete surface with a grinding
wheel or stone, before hammer testing.

 Rebound hammer test should not be conducted on rough surfaces as a result of

incomplete compaction, loss of grout, spalled or tooled concrete surface.

 The point of impact of rebound hammer on concrete surface should be at least

20mm away from edge or shape discontinuity.

 Six readings of rebound number is taken at each point of testing and an average of
value of the readings is taken as rebound index for the corresponding point of
observation on concrete surface.
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Quality of Concrete for different values of rebound number

The advantages of Rebound hammer tests are:

1. Apparatus is easy to use

2. Determines uniformity properties of the surface
3. The equipment used is inexpensive
4. Used for the rehabilitation of old monuments

The disadvantages of Rebound Hammer Test

1. The results obtained is based on a local point

2. The test results are not directly related to the strength and the deformation
property of the surface
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3. The probe and spring arrangement will require regular cleaning and maintenance
4. Flaws cannot be detected with accuracy

Factors Influencing

Below mentioned are the important factors that influence rebound hammer test:

1. Type of Aggregate
2. Type of Cement
3. Surface and moisture condition of the concrete
4. Curing and Age of concrete
5. Carbonation of concrete surface

ULTRASONIC PULSE VELOCITY

This test is done to assess the quality of concrete by ultrasonic pulse velocity method as
per IS: 13311 (Part 1) – 1992.

Principle of this test is – The method consists of measuring the time of travel of an
ultrasonic pulse passing through the concrete being tested. Comparatively higher velocity
is obtained when concrete quality is good in terms of density, uniformity, homogeneity
etc.
Longitudinal pulse velocity (in km/s or m/s) is given by:

v = L/T

where
v is the longitudinal pulse velocity,
L is the path length,

T is the time taken by the pulse to traverse that length.

Equipment for pulse velocity test

The equipment consists essentially of:
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 Electrical pulse generator

 A pair of transducers
 An amplifier
 An electronic timing device for measuring the time interval between the initiation
of a pulse generated at the transmitting transducer and its arrival at the receiving
transducer.

Applications
Measurement of the velocity of ultrasonic pulses of longitudinal vibrations passing
through concrete may be used for the following applications:

 determination of the uniformity of concrete in and between members

 measurement of changes occurring with time in the properties of concrete
 correlation of pulse velocity and strength as a measure of concrete quality.
 determination of the modulus of elasticity and dynamic Poisson's ratio of the
concrete.

Determination of pulse velocity

Transducer arrangement:
The receiving transducer detects the arrival of the pulse. To make measurements of pulse
velocity by placing the two transducers on either:

 opposite faces (direct transmission)

 adjacent faces (semi-direct transmission): or
 the same face (indirect or surface transmission).
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Among the above methods direct transmission will give most desirable results.

Interpretation of Results:
The quality of concrete in terms of uniformity, incidence or absence of internal flaws,
cracks and segregation, etc, indicative of the level of workmanship employed, can thus be
assessed using the guidelines given below
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Factors influencing pulse velocity measurements

 Moisture content

 Temperature of the concrete

 Path length

 Effect of reinforcing bars

 Determination of concrete uniformity

SEMI DISTRUCTIVE TESTING

The semi-destructive testing of concrete is a partial destructive test, where samples are
required for testing. Here small area of the concrete will be damaged during testing.

Chloride penetration test /Rapid Chloride Permeability Test (RCPT)

The rapid chloride permeability test of concrete is an in-situ test to check concrete
permeability. The rapid chloride permeability test of concrete is conducted to check
the Concrete’s Ability to Resist Chloride Ion Penetration.

 This test is very simple and gives results very fast.

 Rapid Chloride Permeability test is done by AASHTO T 277 or ASTM C 1202.

 This test enables the prediction of the service life of concrete structures.

 It can also be utilized for durability-based quality control purposes.

 In this test, the steady voltage (V) is applied to a concrete specimen for 6 hours,
and the current (i) going through the concrete is recorded to find the coulombs.
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 Electric Current is measured in amperes. A coulomb is an ampere – second;

which implies 1 ampere passed through the concrete specimen in 1 second is a 1
coulomb, and the charge passed in 60 seconds would be 60 coulombs.

 The more permeable the concrete, the higher the coulombs; the less porous the
concrete, the lower the coulombs.

Apparatus:

This test apparatus comprises two reservoirs. One of them has 3 % of NaCl solution and
another reservoir has 0.3 M NaOH Solution, Concrete having a thickness of 50
millimeters and diameter 90 to 100 millimeters is used as a test specimen.

Test Procedure:

1. The concrete specimen having a diameter of 100 millimeters and thickness of 50

millimeters is cast and saturated.
2. The concrete sample is placed in between the two reservoirs having NaCl solution
in one reservoir and NaOH solution in the other reservoir.
3. These reservoirs are connected to the DC supply and the voltage of 60 Volts is
applied to the concrete specimen at both ends for six hours.
4. Now measure the current going through the concrete at various time intervals.
5. The current going through the concrete is calculated by an LCD which is
connected to the cell.
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Table for test results:

Charge (Coulombs) Chloride Permeability

>4000 High Permeable Concrete

2000 – 4000 Moderate

1000 – 2000 Low

100 – 1000 Very Low

<100 Negligible

Carbonation;

Carbonation of concrete is a process by which carbon dioxide from the air penetrates
into concrete through pores and reacts with calcium hydroxide to form calcium
carbonates. The conversion of Ca(OH)2 into CaCO3 by the action of CO2 results in a
small shrinkage.

CO2 by itself is not reactive. In the presence of moisture, CO2 changes into dilute
carbonic acid, which attacks the concrete and also reduces alkalinity of concrete (i.e. pH
value reduces).
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The pH value of pore water in the hardened concrete is generally between 12.5 to 13.5
depending upon the alkali content of cement. The high alkalinity forms a thin passivating
layer around steel reinforcement and protect it from action of oxygen and water. As long
as steel is placed in a highly alkaline condition, it is not going to corrode. Such condition
is known as passivation.
The carbonation process is also called depassivation.
In actual practice CO2 present in atmosphere in smaller or greater concentration,
permeates into concrete and carbonates the concrete and reduces the alkalinity of
concrete. The pH value of pore water in the hardened cement paste, which was around
13, will be reduced to around 9.0. When all the Ca (OH)2 has become carbonated, the pH
value will reduce up to about 8.3. In such a low pH value, the protective layer gets
destroyed and the steel is exposed to corrosion. The carbonation of concrete is one of
the main reasons for corrosion of reinforcement.

Factors affecting the carbonation in concrete are:

o Relative humidity (pore water content)

o Grade of concrete
o Permeability of concrete
o Depth of cover of concrete
o Time

Carbonation in concrete can be prevented by:

o Using good quality concrete

o Using dense concrete
o Using a lower water-cement ratio
o Reducing the permeability of concrete
o Increasing the strength of concrete
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Carbonation depth testing

To physically measure the extent of carbonation it can be determined easily by spraying a

freshly exposed surface of the concrete with a 1% phenolphthalein solution. The calcium
hydroxide is coloured pink while the carbonated portion is uncoloured.

The time required for carbonation can be estimated knowing the concrete grade and using
the following equation:

The significance of carbonation is that the usual protection of the reinforcing steel present
in concrete due to the alkaline conditions caused by hydrated cement paste is neutralized
by carbonation. Thus, if the entire concrete cover over the reinforcing steel is carbonated,
corrosion of the steel would occur if moisture and oxygen could reach the steel.

The 1% phenolthalein solution is made by dissolving 1gm of phenolthalein in 90 cc of

ethanol. The solution is then made up to 100 cc by adding distilled water.
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The concrete core is sprayed with phenolphthalein solution, the depth of the uncoloured
layer (the carbonated layer) from the external surface is measured to the nearest mm at 4
or 8 positions, and the average taken.

If the test is to be done in a drilled hole, the dust is first removed from the hole using an
air brush and again the depth of the uncoloured layer measured at 4 or 8 positions and the
average taken. If the concrete still retains its alkaline characteristic the colour of the
concrete will change to purple. If carbonation has taken place the pH will have changed
to 7 (i.e. neutral condition) and there will be no colour change.

RANGE AND LIMITATIONS OF CARBONATION DEPTH MEASUREMENT

TEST

The only limitation is the minor amount of damage done to the concrete surface by
drilling or coring.

Corrosion activity measurement

Several tests for corrosion measurement are given below.

Resistivity Meter
The corrosion of steel in concrete is an electrochemical process that generates a flow of
current. The resistivity of the concrete influences the flow of this current. The lower the
electric resistance, the more easily corrosion current flows through the concrete and the
greater is the probability of corrosion. Thus, the resistivity of concrete is a good
indication of the probability of corrosion.

Resistivity meter can be used to assess the corrosion of steel reinforcement embedded in
concrete. It is a very simple technique and can be adopted easily in the field.
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Open circuit potential (OCP) measurements;

 In reinforced concrete structures, concrete acts, as an electrolyte and the

reinforcement will develop a potential depending on the concrete
environment, which may vary from place to place.
 In this technique, electric potential value (in mV or V) is measured between steel
reinforcement of RC and reference electrode by means of potential electrode,
voltmeter, and connecting wire.
 It indicates the corrosion potential of steel inside RC).
 Thus, the result obtained is a single value that gives an indication of the steel
condition. But, as compared to other NDT for assessment of corrosion in rebars,
this technique is time consuming.

Surface potential (SP) measurements:

 During corrosion process, an electric current flow between the cathodic and
anodic sites through the concrete and this flow can be detected by
measurement of potential drop in the concrete.
 Hence, surface potential measurement is used as a non-destructive testing for
identifying anodic and cathodic regions in concrete structure and indirectly
detecting the probability of corrosion of rebar in concrete.
 This is another useful NDT technique to know the condition of steel rebar
embedded inside the concrete .

Concrete resistivity measurement

 The resistivity method is another electrochemical method, which relies upon the
principle that corrosion is an electrochemical process.
 An ionic current must pass between the anode and cathode areas for corrosion
monitoring of RC structures
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 The resistivity is an indirect indication of active corrosion of the steel

reinforcement.
 The corrosion process will be slower if the resistivity of the concrete is high.
 The resistivity of concrete exposed to chloride indicates the risk of early corrosion
damage, because low resistivity is always associated with rapid chloride
penetration.
 In this technique, the resistivity (ñ) of reinforced concrete, which the current can
easily pass between anode and cathode areas of the concrete is measured (in ohm-
metre) by an equipment consisting of current and potential electrodes, voltmeter or
resistivity unit, and insulated wire.
 This technique for assessment of corrosion level is easy, fast, portable and
inexpensive and thus, can be used for routine inspection

Linear polarization resistance (LPR) measurement

 In this technique, the change in potential during reactions (polarization) is

recorded using an electrode plate on the concrete surface.
 The equipment essentially consists of a reference electrode, counter electrode,
voltmeter, ammeter, and connecting wires.
 The corrosion is evaluated in terms of corrosion current (A/cm2).
 this method requires short time for measurement

Tafel extrapolation

 The Tafel extrapolation technique (TP) is another electrochemical method for

calculating corrosion rate based on the intensity of the corrosion current (Icorr)
and the Tafel slopes.
 Tafel slopes also could be used to calculate corrosion rate with LPR
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Core test

The testing of concrete cores is carried out according to the ASTM Standard C 42.

Testing of Concrete Cores for Strength

 The diameter of core specimens for the determination of concrete compressive

strength should preferably be at least three times the nominal maximum size of
the coarse aggregate used in the concrete or 50 mm.
 The length of the specimen, twice its diameter.
 A core having a maximum height of less than 95% of its diameter before capping
or a height less than its diameter after capping must be rejected. It is preferable to
test the cores in moist condition.
 The ASTM standard prescribes the following procedure: “Submerge the test
specimens in lime-saturated water at 23.0 +/- 1.7° C for at least 40 h immediately
prior to making the compression test.
 Test the specimens after removing from water .
 If the ratio of the length to diameter of the specimen is less than 1.94 apply
correction factors shown in the Table 1.

Table-1: Correction Factor for Ratio of Length of Cone to its Diameter

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The following guidelines are of particular importance in core sampling:

 The number, size, and location of core samples should be carefully selected to
permit all necessary laboratory tests.

 Reinforcing steel should not be included in a core to be tested for strength.

 It is better to drill core through full depth of member to avoid the need of its
breaking for extraction. An extra 50 mm is usually drilled to allow for possible
damage at the base of the core.

 At least three cores must be removed at each location in the structure for strength
determination.
 The hole drilled to take the core is filled by packaged repair material. The material
must not fall down under gravity. In some cases, a precast cylinder of concrete
may be fitted in the core hole by using cement grout or epoxy resin.
 Minimum core diameter is 100 mm but 75 mm and 50mm diameters may be used
in special cases.
 The number of 50 mm diameter cores must be three times the number of 100 mm
diameter cores to get the same accuracy. The 20 percent top portion of member
with a minimum of 50 mm and maximum of 300 mm and a side cover of 50 mm
within the member is preferably not included in the portion of the core to be
tested.

the effect of the length to diameter ratio of the core (R) on the strength is given as under:

For horizontally drilled cores:

Corrected cylinder strength = Core strength x[(2.5x0.8)/(1+(1/R))]
For vertically drilled cores:
Corrected cylinder strength = Core strength x[(2.3x0.8)/(1+(1/R))]
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Load test.
Load test.
Mainly 2 types
 Load test on specimens
 Load test on structure

Load test on specimens

 Compression test
 Split tensile strength test
 Flexural strength test

1. Compression test

The test to find compressive strength of concrete.

Specimens: cubical (15 x 15 x 15 cm )or cylindrical (15 cm in diameter and 30 cm long)

in shape.

Procedure:
 This concrete is poured in the mold and appropriately tempered so as not to have any
voids.

 After 24 hours, moulds are removed, and test specimens are put in water for curing.

 The top surface of these specimen should be made even and smooth. This is done by
placing cement paste and spreading smoothly on the whole area of the specimen.

 These specimens are tested by compression testing machine after seven days curing or 28
days curing.

 Load should be applied gradually at the rate of 140 kg/cm2 per minute till the Specimens
fails.

 Load at the failure divided by area of specimen gives the compressive strength of
concrete.

2. Split tensile strength test

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To find tensile strength of concrete.

Specimens: cylindrical (15 cm in diameter and 30 cm long) in shape.

Procedure

 wet specimen from water after 28 of curing is used for tensile strength estimatimation.
 record the weight and dimension of the specimen.
 Set the compression testing machine for the required range.
 Place plywood strip on the lower plate and place the specimen.
 Align the specimen
 Place the other plywood strip above the specimen.
 Bring down the upper plate so that it just touch the plywood strip.
 Apply the load continuously without shock at a rate within the range 0.7 to 1.4 MPa/min (1.2
to 2.4 MPa/min based on IS 5816 1999)
 Finally, note down the breaking load(P)

3. Flexural strength test

Specimen: The standard size of the specimens are 15 x 15 x 70 cm. Alternatively, if the largest
nominal size of the aggregate does not exceed 20 mm, specimens 10 x 10 x 50 cm may be used.

Loading :
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Procedure:
 The specimen is then placed in the machine in such a manner that the load is applied to
the uppermost surface as cast in the mould, along two lines spaced 20.0 or 13.3 cm apart.
 The axis of the specimen is carefully aligned with the axis of the loading device.
 The load is applied without shock and increasing continuously, at a rate of loading of 400
kg/min for the 15.0 cm specimens and at a rate of 180 kg/min for the 10.0 cm specimens.
 The load is increased until the specimen fails, and the maximum load applied to the
specimen during the test is recorded.
 The appearance of the fractured faces of concrete and any unusual features in the type of
failure is noted.
The flexural strength of the specimen is expressed as the modulus of rupture fb . if
‘a’ equals the distance between the line of fracture and the nearer support, measured on the
centre line of the tensile side of the specimen, in cm,

fb When ‘a’ is greater than 20.0 cm for 15.0 cm specimen or greater than 13.3 cm for a10.0 cm
specimen, or

when ‘a’ is less than 20.0 cm but greater than 17.0 cm for 15.0 specimen, or less than 13.3cm but
greater than 11.0 cm for a 10.0 cm specimen where b = measured width in cm of the specimen,
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Load test on structure

The procedure basically involves loading the structure in a monotonic manner by

gradually applying the load until reaching the test load magnitude, which is maintained
for 24 hours.

The procedure of load test on concrete structures presented here depends on ACI -2008
Chapter 20.
A load test is usually not made until the portion of the structure to be subjected to load is
at least 56 days old. If a load test is decided as a means of the strength evaluation process
for a particular project, the first step is that
 all the involved parties decide and
 agree upon the region to be loaded,
 the magnitude of the load,
 the physical load test procedure, and
 acceptance criteria.
the loads, extra concrete strength and multi-directional sharing of the loads not
considered in ordinary designs.

 Load Arrangement for Physical Load Test on Concrete Structures

a) The spans and panels having more doubt during survey are considered.

b) The number and arrangement of spans or panels loaded are selected to maximize the
deflection and stresses in the critical regions of the structural elements to be tested.
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c) The load is applied at locations where its effect on the suspected defect is a maximum.

2. Load intensity for Physical Load Test

The total test load is taken larger of the following three values:

(a) 1.15D + 1.5L + 0.4(Lr or S or R) – De

(b) (b) 1.15D + 0.9L + 1.5(Lr or S or R) – De
(c) (c) 1.3D – De

Where, D is the total dead load,

L is the live load on floors,
Lr is the roof live load,
S is the snow load,
R is the rain load and
De is the dead load already in place.
The live load L can be reduced as allowed by the building code.
The load factor on the live load L in (b) is allowed to be reduced to 0.45
except for garages, areas occupied as places of public assembly, and all areas
where L is greater than 4.8 kN/m2.

 Loading criteria

1. Before conducting the test, it must be made sure that the structure does not fully
collapse under the test load and sufficient safety measures must be taken to save the
working people and other parts of the building in case of an unexpected sudden
failure. Safety measures adopted for the testing must not interfere with load test
procedures and these must not affect results.

2. Establish failure criteria before the test.

3. Carefully think about the types of expected cracks, method of measuring the width and
length of expected cracks, expected locations where the cracks will be measured, and
approximate limits for opening and development of cracks.

4. Deflection gages are installed on all critical sections. Measurements must be made at
locations where maximum response is expected. Additional measurements can be made if
required.
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5. The initial value for all applicable response measurements (such as deflection, rotation,
strain, slip, crack widths) are recorded not more than 1 hour before application of the first
load increment.

6. A load equal to service dead load D that is not already present, such as for partitions,
false ceilings and ducts, must be applied and it should remain in place until the
completion of the load test. Deflection readings are taken immediately after the
application of this additional load. The test can be started after an interval of 48 hours.
After dead load deflections have stabilized, existing cracks and other defects must be
observed, marked, and recorded.

7. Test load defined above is applied in approximately four or more equal increments. It
is better to carry out visual inspection of the structure after each load increment.

8. Uniform test load is applied in a manner to ensure uniform distribution of the load to
the portion of the structure being tested. The loading units placed on the surface must not
have bridging or arching between them because this may make the load non-uniform with
reduction of load near the mid-span.

9. All response measurements are made after each load increment.

10. If the measured deflections exceed expected values, the test must either be stopped or
a written permission must be taken from the supervising engineer.

11. After each increment of the load, the formation or worsening of cracking and distress,
and the presence of excessive deformations, rotations, etc., must be carefully observed.
The investigator must approximately analyze the observed data and determine whether it
is safe to proceed with the next increment. It is advantageous that load-deflection curves
are developed during the load test for all critical points of deflection measurements.

12. Maintain the full test load on the structure for at least 24 hours and record all response
measurement after this time interval.

13. Total test load is removed in the least possible time after all response measurements
are made in the above step.

14. Wait for 24 hours after the removal of the entire test load. All the response
measurements are made after 24 hours again.

15. Physical load testing is basically used only for evaluating the strength of a structure
for vertical gravity loads. Leaving some exceptions, in-situ load testing is not used for
evaluating the strength of a structure against lateral loads.
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Pullout test:
The fundamental principle behind pull out testing is to correlate to the compressive strength of
concrete. This correlation is achieved by measuring the force required to pull a steel disc or ring,
embedded in fresh concrete, against a circular counter pressure placed on the concrete surface
concentric with the disc/ring.
Depending upon the placement of disc/ring in he fresh concrete, pull out test can be divided into
2 types,

1. LOK test

2. CAPO test

LOK Test:
The LOK-TEST system is used to obtain a reliable estimate of the in-place strength of concrete
in newly cast structures in accordance with the pullout test method described in ASTM C900, BS
1881:207, or EN 12504-3.

 A steel disc, 25 mm in diameter at a depth of 25 mm, is pulled centrally against a 55 mm

diameter counter pressure ring bearing on the surface.
 The force F required to pullout the insert is measured.
 The concrete in the strut between the disc and the counter pressure ring is subjected to a
compressive load. Therefore the pullout force F is related directly to the compressive
strength.
CAPO test (Cut and Pull out Test)
 The CAPO-TEST permits performing pullout tests on existing structures without the
need of preinstalled inserts.
 CAPO-TEST provides accurate on-site estimates of compressive strength. Procedures
for CAPO-TEST, are included in ASTM C900 and EN 12504-3.
 When selecting the location for a CAPO-TEST, ensure that reinforcing bars are not
within the failure region.
 The surface at the test location is ground using a planing tool and a 18.4 mm hole is made
perpendicular to the surface using a diamond-studded core bit.
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 A recess (slot) is routed in the hole to a diameter of 25 mm and at a depth of 25 mm.

 A split ring is expanded in the recess and pulled out using a pull machine reacting
against a 55 mm diameter counter pressure ring.
 the ultimate pullout force F is related directly to compressive strength.

PENETRATIONRESISTANCE OR WINDSOR PROBE TEST

The Windsor probe, like the rebound hammer, is a hardness tester that the penetration of the
probe reflects the compressive strength.

Purpose of Penetration Resistance Test

1. Determine the uniformity of concrete

2. Specify exact locations of poor quality or deteriorated concrete zones
3. Assess in-place strength of concrete

The Windsor probe consists of

 a powder-actuated gun or driver
 hardened alloy steel probes
 loaded cartridges
 a depth gauge for measuring the penetration of probes
 other related equipment.

PROCEDURE FOR WINDSOR PROBE TEST

1. Place the positioning device on the surface of the concrete at the location to be tested.
2. Mount a probe in the driver unit
3. Position the driver in the positioning device
4. Fire the probe into the concrete.
5. Remove the positioning device and tap the probe on the exposed end with a small
hammer to ensure that it has not rebounded and to confirm that it is firmly embedded.
6. Place the measuring base plate over the probe and position it so that it bears firmly on the
surface of the concrete without rocking or other movement.

Results
The penetration resistance of concrete is computed by measuring the exposed length of
probes driven into concrete. In order to estimate concrete strength, it is necessary to
establish a relationship between penetration resistance and concrete strength.
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