NON DESTRUCTIVE
TESTING
IN RAILWAY BRIDGES
INTRODUCTION
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Non – Destructive testing [NDT] is an
activity to assess the variation from the
design and monitor performance.
With the increasing number of structures
showing signs of distress a greater need is
felt to apply more advance assessment
techniques and equipment in the bridge
inspection.
This presentation focuses on the available
techniques , and two nos case studies of
NF Railway , where the NDT has been
used successfully.
NDT Techniques
Compressive Strength
Rebound Hammer Test, Windsor
Probe Test , Core Test , Lok Test,
Capo Test
Flexural Strength
Break- Off Test
Direct Tensile Strength
Pull- Off Test
Homogeneity
Ultrasonic Pulse Velocity Test ,
Acoustic Emission Method , Pulse –
echo method. Gamma- Ray
Radiography , Endoscopy, Integrity
Testing of Piles
Permeability
Initial Surface Absorption Test , Figg’s
Air and Water Permeability Test
NDT Techniques [… Contd]
Chemical Composition
Wet Chemical Analysis for Total
Chloride , Potential Measurement
Technique for Chlorides,
Determination Carbonation Test
Cracks
Ultrasound Pulse Velocity Test,
Acoustic Crack Detector , Dye
Penetration Test , X-Ray Radiography
, Gamma Radiography
NDT in NF Railway`
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Of the above NDT techniques so detailed ,
NF Railway has gained some experience
in the following techniques
A. Rebound Hammer Test
B. Core Test
C. Ultra Sound Pulse Velocity Method
D. Integrity Testing of Piles
E. Chemical Analysis of the Concrete
Material
NDT in NF Railway
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The experienced so gained in the last
two years on NF Railway shall be
explained in the remaining part of
the presentation using two nos case
studies of NF Railway
NDT in NF Railway --- Br No 40
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Br No 40 is an Important Bridge on New
Jalpaiguri – New Bongaigaon section of NF
Railway having an span of 20 x 150 feet over
Teesta River. Its design discharge is 700000
cusecs. It has Cement Concrete Well Foundation
designed for BGML Standard with 30 Feet Well
Dia and 100 feet depth of well below HFL. The
bridge was initially constructed as 13x150 feet
spans . During 1988 floods eastern approach was
washed away and the bridge was extended by 7
spans of 150ft on the east in 1975.
For the last few years cracks were developing on
Pier No. P1, P2 , P3 and P4.
NDT in NF Railway --- Br No 40
PANORAMIC VIEW OF BRIDGE NO 40
NDT in NF Railway --- Br No 40
ZIG ZAG CRACK PATTERN
NDT in NF Railway --- Br No 40
CRACKS IN WELL CAP
NDT in NF Railway --- Br No 40
SHOWING CASTING LIFT VARIATIONS
NDT in NF Railway --- Br No 40
HORIZONTAL CRACKS FORMED DUE TO SEPERATION OF COLD
JOINT IN COURSE OF TIME
NDT in NF Railway --- Br No 40
CRACK MAGNIFIED
NDT in NF Railway --- Br No 40
SEVERE VERTICAL CRACKS
NDT in NF Railway --- Br No 40
CRACKS CONCENTRATION FROM DIFFERENT DIRECTIONS ,
RESULTING IN SEVERE DETERIORATION AT MEETING POINT
NDT in NF Railway --- Br No 40
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These cracks were prominent in Piers P1,
P2, P3 and P4.
After this visual examination , certain
points remained unanswered
It was not clear , as to what was the
depth of these cracks?
What was the resultant compressive
strength of the concrete mass used in
Pier?
Whether the concrete has undergone any
long term deterioration due to excessive
sulphur or chloride content?
NDT in NF Railway --- Br No 40
In order to assess the above points it
was decided to undertake the
following examinations
 Ultrasonic Pulse Velocity Test
 Concrete Core extraction for
evaluation of compressive strength
 Chemical Analysis to ascertain
approximate mix proportions of
concrete

NDT in NF Railway --- Br No 40
M/s S. K. Mitra and Associates of
Kolkatta were entrusted the work,
who carried out the same in March –
April 2003
 Test Methods and the deductions on
the basis of the test results are
explained in the following slides.
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NDT in NF Railway --- Br No 40
Ultrasonic Pulse Velocity Test
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The aim of the Ultrasound pulse velocity test was
to identify weak locations possessing loss of
integrity , presence of void , quality of concrete
and depth of cracks which could not be
ascertained by visual inspection.
The ultrasonic pulse is generated by an electroacoustical transducer. When the pulse is induced
in the concrete from a transducer, it undergoes
multiple reflections at the boundaries of the
different material phases within the concrete. A
complex system of stress waves is generated
which includes longitudinal , shear and surface
waves. The receiving transducer detects the
longitudinal waves which is the fastest.
NDT in NF Railway --- Br No 40
Ultrasonic Pulse Velocity Test
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The velocity of an ultrasonic pulse through any
material depends upon its density , modulus of
elasticity , presence of reinforcement steel and
Poisson’s ratio.
The underlying principle of assessing the quality
of concrete is that comparatively higher velocities
are obtained when the quality of concrete in
terms of density , homogeneity and uniformity is
good. In case of poorer quality , lower velocities
are obtained.
If there is a crack , void or flaw inside the
concrete which comes in the way of transmission
of the pulses, the pulse strength is attenuated
and lower velocities are obtained,
NDT in NF Railway --- Br No 40
Ultrasonic Pulse Velocity Test
Test Pulse Velocity by Concrete Quality
Cross Probing
Grading [IS
[Km/sec]
13311Part –I-1992]
1
Above 4.5
Excellent
2
3.5 to 4.5
Good – Very Good
3
3.0 to 3.5
Medium
4
Below 3.0
Doubtful
NDT in NF Railway --- Br No 40
Ultrasonic Pulse Velocity Test-Interpretations
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There are two dimensions to the result
interpretation
First – General Quality Assessment of
Concrete- The velocity ranged fro 3.1 to
4.0 Km/sec. This indicates that quality of
concrete was good to very good
Second- Depth of Crack – It was assessed
based on the velocity of propagated waves
on both sides of the crack. Crack Depth
were found to be varying from 31mm
to 684 mm .
NDT in NF Railway --- Br No 40
Concrete Core Extraction
The basic purpose to extract cores
was to evaluate directly the
compressive strength of concrete on
the basis of cylinder strength and corelate it to conventional cube
strength.
 This gives fairly a good idea about
the compressive strength reached
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NDT in NF Railway --- Br No 40
Concrete Core Extraction
CORE DRILLING IN OPERATION
NDT in NF Railway --- Br No 40
Concrete Core Extraction
CORE LOCATION AFTER DRILLING
NDT in NF Railway --- Br No 40
Concrete Core Extraction
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5 Cores of 55mm Diameter were extracted.
To assess crushing strength , cores were trimmed
at the end and tested for voids and density also.
Prior to test , cores were capped with sulphur and
tested after soaking for 48 hours
Equivalent concrete cube strength was assessed
as per IS 516-1959. The results obtained were
found nearer to M-20 grade concrete.
As per the completion plan , a mix proportion of
1:3:6 is mentioned in the drawing for
construction of pier , and the bed block and well
cap was constructed using mix proportion of
1:2:4. The test results confirmed that the
compressive strength of the concrete is
above the assumed value.
NDT in NF Railway --- Br No 40
Concrete Core Extraction- Test Results
Sample
No
Length
[cm]
% of Water Crushing
Absorption Strength in
N/sq mm
Eq Cube
Strength in
N/sq mm
C1
15.8
2.47
23.78
29.2
C2
16.4
3.04
19.83
24.8
C3
13.8
3.98
17.91
22.39
C4
12
3.59
18.40
23.00
C5
14.6
4.96
18.54
23.17
NDT in NF Railway --- Br No 40
Chemical Analysis
The aggregates of Cement Concrete
sample was separated from the
mortar mechanically and chemical
analysis of mortar portion of the
cement concrete was carried out
generally on the lines of ASTM C-8566.
 PH value , Chloride content and the
Sulphate Content were analysed.
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NDT in NF Railway --- Br No 40
Chemical Analysis- Test Results
Test
C1
C2
C3
C4
C5
PH at
>10. >10.5 >10.5 >10.5 >10.5
31Deg C 5
Chloride
in PPM
247
74
Sulphate 3087 4013
in PPM
25
74
97
3498
5145
5728
NDT in NF Railway --- Br No 40
Chemical Analysis- Test Results
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As per IS 456 -2000 , the PH should not be less
than .Test results reveals that concrete is basic in
nature and so no deterioration due to acidic
nature was envisaged.
As per IS 456 – 2000 , the chloride content
should be below 3000 ppm . In all the samples
the Chloride content was found to be much below
this
The limiting value of the sulphate content is 4000
ppm . In this case the sulphate content were
found to be near or slightly more than the
limiting value. As per IS 456-1978 , higher
values of sulphates can cause expansion
and disruption of concrete.
NDT in NF Railway --- Br No 40
Chemical Analysis- Test Results
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IS 456-2000 Clause 8.2.5.4 states that,
some aggregates containing particular
varieties of silica may be susceptible to
attack by alkalis originating from cement
and other sources producing an expansive
reaction which can cause cracking and
disruption of concrete.
Aggregates retrieved from the extracted
core was subjected to aggregate reactivity
test as per IS:2386 and the results ruled
out the possibility of AlkaliAggregate reactivity
NDT in NF Railway --- Br No 40
CONCLUSIONS
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Compressive Strength of Concrete was
found to be more than the design value.
Crack depth was found to be varying
between 31mm to 684 mm
Horizontal Cracks , noted in between the
lifts of casting in some cases were due to
cold joints formed during construction.
Higher sulphate content might have
resulted in the cracks.
NDT in NF Railway --- Br No 184
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Br No 184 is a major bridge in Guwahati –
Lumding section of NF Railway . This has span of
1x 12.20m and 3x 18.30m . The bridge was built
between 1930-1935 . It is having well
foundations
Interestingly the bridge pier is of concrete with
one brick thick cladding all around the pier.
AEN/Lumding reported a hollow echoing sound
emanating from the piers peropheri , when the
piers were struck by hammers at different points
along the cross section and height of the
piers.Sectional Sr DEN imposed a restriction of 20
kmph over the bridge. The Division proposed
rebuilding of the bridge at an approximate cost of
Rs 5.16 Crores
NDT in NF Railway --- Br No 184
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CBE’s inspection revealed that apart from
the usual weathering of the bricks , there
was no distress noticeable on the outer
face of the piers where the hollow sounds
were coming from
CBE decided to carry out the NDT and
have an insight into the bridge structural
behaviour before going for the complete
rebuilding.
NDT in NF Railway --- Br No 184
M/s S K Mitra & Associates were
entrusted to carry out the NDT using
the following techniques
 Ultra sound pulse velocity test
 Core extraction and Testing
 Chemical test to evaluate sulphate .
Chloride content and PH value
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NDT in NF Railway --- Br No 184
UPV Test
MEASURING ULTRA SONIC PULSE VELOCITY
NDT in NF Railway --- Br No 184
UPV Test
MEASURING PULSE VELOCITY
NDT in NF Railway --- Br No 184
UPV Test
Test Pulse Velocity by Concrete Quality
Cross Probing
Grading [IS
[Km/sec]
13311Part –I-1992]
1
Above 4.5
Excellent
2
3.5 to 4.5
Good – Very Good
3
3.0 to 3.5
Medium
4
Below 3.0
Doubtful
NDT in NF Railway --- Br No 184
UPV Test
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Interestingly , the velocity of pulse ranged
from 0.668 to 1.45km/sec for Pier No 2
and from 0.673 to 1.32 Km/sec for Pier No
P3
This placed the concrete quality as
doubtful according to the UPVvalues as
per IS:13311(Part I)
Next Logical step was to carry out the
Concrete Core Strength Tests and do the
Chemical Analysis.
NDT in NF Railway --- Br No 184
CONCRETE Core Cutter Test
CORE EXTRACTION IN PROGRESS
NDT in NF Railway --- Br No 184
CONCRETE Core Cutter Test
AFTER CORE EXTRACTION
NDT in NF Railway --- Br No 184
CONCRETE Core Cutter Test
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Total 7 Nos cores of 50 mm dia were
extracted. Out of these , 2 Cores were
extracted from the brick layer to assess
the quality of the bricks
In all cases , water absorption test was
carried out and strength determined as
per the procedure described in IS:516. To
assess crushing strength , cores were
trimmed at the end and tested for void
and density.
NDT in NF Railway --- Br No 184
CONCRETE Core Cutter Test
Sample
No
Length
[cm]
% of Water Crushing
Absorption Strength in
N/sq mm
Eq Cube
Strength in
N/sq mm
C1
20
6.4
7.85
9.81
C2
1916.4
6.1
13.0
16.25
C3
18
6.7
11.0
13.75
C4
19
3.5
34.7
43.40
C5
20
5.0
18.3
22.90
NDT in NF Railway --- Br No 184
CONCRETE Core Cutter Test
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The results obtained were nearer to M15 ,
excepting in two cases where these were
found nearer to M10 and M40 respectively.
Hence the quality of concrete was found to
be good in general
Concrete cores also displayed a lot of
voids and honeycombing at the interface
of the concrete core and brick cladding.
NDT in NF Railway --- Br No 184
Chemical Analysis
From the cores extracted , the
aggregate was separated from the
mortar
 From the chemical test result it was
concluded that , the concrete was
basic in nature. Chloride and
Sulphate content of the concrete was
well below the limit prescribed by
IS456.
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NDT in NF Railway --- Br No 184
Condition Monitoring and
Useful Life Assessment
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The results as obtained were conveyed to
Prof P. Banerjee of IIT-Powai. Pixel
Networks of Mumbai arranged for the site
visit and investigation of the bridge .
On 14th January 2004, Prof Banerjee
visited the site and . Two more cores were
extracted from the bridge in his presence
as requested by him.
He submitted his detailed report
afterwards
NDT in NF Railway --- Br No 184
CONCLUSIONS based on the NDT and
Prof Banerjee’s Report
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The hollow sound emanating form the pier
was due to the voids and honeycombing
formed at the face of pier and brick
cladding.
Lower pulse velocity was also due to the
voids and honeycombing at the interface
Concrete Core was of fairly good quality
and was found to be having sufficient
strength to carry the present day loading
There was no deterioration due to acidity ,
higher chloride content or higher sulphate
content.
NDT in NF Railway --- Br No 184
CONCLUSIONS based on the NDT and
Prof Banerjee’s Report
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While calculating the strength of the
bridge it was assumed that the brick
cladding was not participating in any load
sharing arrangement.
Hollow sound was not a cause of concern.
The Railway got confidence in the
structural integrity of the bridge and the
rebuilding of the bridge was not
considered necessary
NDT in NF Railway --- Br No 184
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The Cost of the NDT was Rs 1.6 Lakh and
the cost of Conditional monitoring by Prof
Banerjee was Rs 2.5 Lakh
The cost of rebuilding of the bridge was Rs
5.2 Crores.
Not only the NDT resulted in the huge
saving , it also initiated an approach which
is scientific , logical and extends beyond
the realms of judgments based solely on
the visual examinations
THANK YOU