Study on soundness of reinforced concrete structures by ndt approach

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Special Issue: 06 | May-2014 | RRDCE - 2014, Available @ http://www.ijret.org 265
STUDY ON SOUNDNESS OF REINFORCED CONCRETE STRUCTURES
BY NDT APPROACH
Lokesh V1
, B. Shivakumara Swamy2
, S.Vijaya3
1
PG Student, civil engineering dept., Dr.AIT Bangalore, Karnataka, India
2
Head of the department, Civil engineering department, Dr.AIT, Bangalore, Karnataka, India
3
Prof., Civil engineering department, Dr.AIT, Bangalore, Karnataka, India
Abstract
Non-Destructive Evaluation (NDE) techniques, are being used for Structural Health Evaluation. Structures are assemblies of load
carrying member capable of safely transferring the superimposed loads to the foundations. Their main and most looked after property
is the strength of the material that they are made of. Concrete, as we all know, is an integral material used for construction purposes.
Thus, strength of concrete used, is required to be ‘known’ before starting with any kind of analysis. The various methods and
techniques, called as NDT. In recent years, innovative NDT methods, which can be used for the assessment of existing structures, have
become available for concrete structures, but are still not established for regular inspections. Therefore, the objective of this project is
to study the applicability, performance, availability, complexity and restrictions of NDT.
Key Words: Non Destructive Evaluation(NDE), Structural Health Evaluation, profometer half cell potentiometer,
carbonation test, quality/strength, Structural health and reinforcement etc…
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1. INTRODUCTION
Structural health monitoring is at the forefront of structural
and materials research. Structural health monitoring systems
enable inspectors and engineers to gather material data of
structures and structural elements used for analysis. Ultrasonic
can be applied to structural monitoring programs to obtain
such data, which would be especially valuable since the wave
properties could be used to obtain material properties.
Any structure that is in use for which it is intended to, shows
some structural disorder, requires to be assessed for its quality,
structural integrity and in place concrete compressive strength.
Standing structure can not be assessed by conventional
methods adopted to evaluate structural integrity and in place
concrete compressive strength same as by testing standard
specimens up to failure. Hence for structures, standing decades
together, an efficient system of assessment of structure for in
place strength is urgently required. It is also true to the new
structures, as more and more clients and their consultants are
well aware of the quality assurance in booming infrastructure
sector in India. Non Destructive Testing ( NDT ) has the
potential of becoming an effective tool for quality assurance
and damage assessment.
2. NON-DESTRUCTIVE METHODS
The objective of a non destructive test is to obtain an estimate
of properties of material by measuring certain quantities which
are empirically related to it. To make a strength estimation, it
is necessary to know the relationship between the result of the
non destructive test and strength of material. The accuracy of
interpretation of results depends directly on the correlation
between strength of material and measured quantity. Thus, the
user of NDT should have an understanding of what quantity is
measured by the test and how this quantity is related to the
strength of material. Test methods range widely in reliability
and complexity. Hence, appropriate experience is necessary in
selection of the proper tests and corrects interpretation. The
following NDT techniques are generally employed -
1. Schmidt‟s Rebound Hammer test for assessing the concrete
compressive strength.
2. Ultrasound pulse Velocity tests for establishing quality of
concrete.
3. Coring for taking out concrete cores for laboratory testing
for determining compressive strength.
4. Rebar locator tests for locating reinforcement bars and for
determining their diameters and spacing.
5. Carbonation test for determining the depth of carbonation of
concrete.
6. Half- cell potential test for determining the likelihood of
corrosion.
7. Determination of chloride contents of concrete
In the present paper, health assessment methods such as A)
Rebar locator test B) Carbonation test and C) Half- cell
potential test are closely scrutinized to explore some
fundamental aspects of R. C. structure health monitoring.

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2.1 Profometer/Rebar Locator
It is used for detecting location and size of the reinforcement,
and the concrete cover.This instrument is also known as rebar
locator. The method is based on measurement of the change in
electromagnetic field caused by the steel embedded in the
concrete. It is covered by BS 4408:1969-Part1. The device is a
portable and handy instrument, normally used to locate the
reinforcement, with an electronic display. To ensure
satisfactory working of profometer and to get accurate results,
it should be calibrated before starting the operations and at the
end of the test. To check the calibration accuracy, the size and
cover of the reinforcement of the test block is measured at
different locations on test block and the recorded data should
match with the standard values prescribed on the test block.
Path measuring device and spot probes are together used for
path measurements and scanning of reinforcement bars. These
are connected with profometer and are moved on the concrete
surface for scanning the reinforcement bars and measuring the
spacing. Diameter and depth probes are used in conjunction
with the profometer to measure the diameter of rebar and its
concrete cover respectively For carrying out this test, proper
access to the test section is essential. Before actual scanning,
marking is done with chalk on the concrete surface by dividing
it into panels of equal areas. The method is very fast and gives
quite accurate results if the reinforcement is not heavily
congested. The equipment is light and a single person can
perform the test.
Fig 1 profometer
2.2 Half Cell Potentiometer Test/Corrosion Analyzer
Electrochemical Half-cell Potentiometer test provides a
quantitative assessment of reinforcement corrosion over a
wide area without the need of major removal of the concrete
cover. The method detects the likelihood of corrosion of steel
but cannot indicate the rate of corrosion. Distinction can be
made between corroded and non-corroded locations by
making measurements over the whole surface.
Principle and code: Corrosion analyzer is based on electro-
chemical process to detect corrosion in the reinforcement bars
of structure. During active corrosion, the steel-concrete system
in the reinforced concrete element represents short-circuited
galvanic cell, with the corroding area of the reinforcement bar
acting as the anode, the passive surface as the cathode and
concrete as electrolyte. The excess electrons generated during
corrosion flow through the concrete between anodic and
cathodic sites, generating current which is accompanied by an
electric potential field surrounding the corroding bar. The
equipotential lines intersect the surface of the concrete and the
potential at any point can be measured using the half potential
method.
Device and Methodology: Before starting the test, the test
surface is made wet (this should be done at least 45 minutes
prior to conducting the test). To measure half-cell potentials,
an electrical connection is made, through a small drilled hole)
to the steel reinforcement in the concrete member to be tested.
This is connected to a high impedance digital millivolt meter,
often backed up with a data logging device. The other
connection to the millivolt meter is taken to a copper/copper
sulfate or silver/silver chloride half-cell, which has a porous
connection at one end which can be touched to the concrete
surface. This will then register the corrosion potential of the
steel reinforcement nearest to the point of contact.
2.3 Carbonation Test
Carbonation test was carried out on RC members at random
using phenolphthalein indicator in 0.1 N methyl alcohol
solution to assess the extent of carbonation in cover concrete.
Carbonation of concrete occurs when the carbon dioxide, in
the atmosphere in the presence of moisture, reacts with
hydrated cement minerals to produce carbonates, e.g. calcium

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carbonate. The carbonation process is also called
depassivation. Carbonationpenetrates below the exposed
surface of concrete extremely slowly. The time required
forcarbonation can be estimated knowing the concrete grade
and using the following equation:
Where
t is the time for carbonation,
d is the concrete cover,
k is the permeability.
Typical permeability values are shown in Table 5.1.
2.3.1. Equipment for Carbonation Depth
Measurement Test
If there is a need 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.
2.3.2. General Procedure for Carbonation Depth
Measurement Test
The 1% phenolpthalein solution is made by dissolving 1gm of
phenolpthalein in 90 cc of ethanol. The solution is then made
up to 100 cc by adding distilled water. On freshly extracted
cores the 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.
2.3.3. Range and Limitations of Carbonation Depth
Measurement Test
The phenolphthalein test is a simple and cheap method of
determining the depth of carbonation in concrete and provides
information on the risk of reinforcement corrosion taking
place. The only limitation is the minor amount of damage
done to the concrete surface by drilling or coring.
3. APPLICATIONS
Nondestructive testing has wide application in the field of civil
engineering. Nondestructive testing can be carried out to know
about feasibility and soundness of the structure In order to
ascertain the structural soundness of the building for the
proposed additional floor construction, following studies were
carried out:
1. Dimensional measurement of structural members.
2. Examination of foundation and tests on soil at foundation
level.
3. Semi-destructive test to assess the quality/strength of in-situ
concrete in RC footings
4. Non-destructive tests to assess the quality/strength of in-situ
concrete in RC member
 Ultrasonic pulse velocity test on RC columns and
beams
 Rebound hammer test on RC slabs.
5. Cover meter studies to map the disposition and probable dia
of peripheral rebars in RC members
6. Theoretical analysis and design verification for the
proposed additional floor
Depending on the results the strength of existing structure is
evaluated.
4 CONCLUSIONS
In this study, various non-destructive condition evaluation
methods have been studied and they have been used in the
field testing of reinforced cement concrete structural members
REFERRENCES
[1]. Guidebook on non destructive testing of concrete
structures International atomic energy agency, Vienna, 2002
[2]. Handbook on Non Destructive Testing of Concrete”
(second edition) by V.M. Malhotra and N.J. Carino

Study on soundness of reinforced concrete structures by ndt approach

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