International Journal of Engineering and Applied Sciences (IJEAS)
ISSN: 2394-3661, Volume-9, Issue-1, January 2022
Concrete Structure Crack Measuring Devices - A Case
Study of Concrete Dam
Rajkumar Prasad, Mahabir Dixit
ABSTRACT - Cracking is a common phenomenon structure. Cracks can be sign of structural problems, or a
observed in many concrete structures. The cracks can result of concrete deterioration. Several issues can result
develop due to consequence of plastic shrinkage or
in cracks in concrete, including excessive external loads,
constructional movements, overloading concrete
elements, creep, chemical reactions inclusive of alkali- external restraint forces, internal restraint forces,
aggregate reactions and corrosion etc. Crack width and differential movements and settlement etc. In a concrete
depth are two important parameters used to determine element, the crack (shrinkage, thermal, and service loads)
the extent and severity of existing cracks. Crack width and distribution is mainly controlled by steel
monitoring and control procedures are essential to assess
reinforcement. In fiber-reinforced concrete, fibers help
stability of the structure and quantify the development of
the damage. This paper discusses different instruments/ control cracking. Cracks that are also caused by internal
methods available for evaluation of crack along with a or external chemical reactions, or a result of accidental
case study of crack monitoring of 92 m high concrete loads i.e. blast, or impact load from accidents. These
gravity dam. cracks are different in their nature and require further
investigation to assess their impact on structural integrity
Index Terms: - Crack, Physical, Chemical, Alkali Aggregate and durability performance of the element.
Reaction, Plastic, Groutable, Triaxial etc.
1. INTRODUCTION 2.1 CRACKING IN CONCRETE DAM
A crack is a linear fracture in concrete element which In concrete dams, cracks are formed mainly due to
extends partly or completely through it. In a concrete shrinkage of concrete due to temperature variations.
element, tensile stresses are initially carried by the These cracks may develop internally in the body of the
concrete and reinforcement. When the tensile stresses in dam or externally on the surface of the dam. Surface
cracks are more dangerous than interior cracks. Figure 2
the element exceeds the strength of concrete, the concrete
cracks and tensile force is transferred entirely to presents a typical example of crack in concrete dam.
reinforcement. Figure 1 shows a typical diagram of crack
in concrete element.
In concrete dams, cracks are formed mainly due
to shrinkage of concrete due to temperature variations.
These cracks may develop internally in the body of the
dam or externally on the surface of the dam. Surface
cracks are more dangerous than interior cracks.
Figure 2: Crack in concrete dam
3. EVALUATION OF CRACK
Visual inspection and monitoring is the first step towards
understanding the nature of existing cracks, and the
Figure 1: Crack in Concrete Element underlying causes. For example, inclined cracks over
concrete beams near the supports can be a sign of shear
stress, or cracks with a sign of rust can be a result of steel
2. CAUSES FOR CONCRETE CRACKS
corrosion. Usually, crack widths are used to assess the
Cracks can occur during the concrete construction, severity of concrete cracks, whereas crack depth is used
placement and curing and during the service life of the to evaluate overall structural integrity of the element.
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International Journal of Engineering and Applied Sciences (IJEAS)
ISSN: 2394-3661, Volume-9, Issue-1, January 2022
3.1 CRACK WIDTH
Crack severity on the surface of concrete is normally
measured using a crack width ruler. Depending on the
opening of the cracks on the surface, cracks can be
described (as tiny as hairline, or severe (few millimeters
opening). Different methods to monitor crack width
changes will be discussed further.
Fig.3: Crack Width Steel Ruler
3.2 CRACK DEPTH
4.2 PLASTIC TELL-TALE
Evaluation of Crack depth measurement is important to
make sure if surface cracking is well propagated into It is the most famous system used to monitor crack width
concrete or not. The depth of cracks in concrete can be variation. Plastic tell-tale consist of two plates which
measured by using Impact Echo method or Ultrasonic overlap for part of their length. One plate is calibrated in
Pulse Velocity method. Crack depth is used to evaluate millimeters and the overlapping plate is transparent and
structural integrity, and verify durability performance. marked with a hairline cursor. The plate with scales
UPV utilizes ultrasonic wave propagation to measure the marked in millimeter units of measurement is fixed on
depth of cracks in concrete. UPV measures the transit one side of the crack and the other plate marked with
time of the ultrasonic waves distance on concrete and be cursor is fixed on opposite side of the crack as it is shown
analyze as the speed of the wave. The effectiveness of in Figure 4. The instrument is screwed on the wall in such
repair methods such as epoxy injection relies on accurate a way that the cursor of one plate and the middle of the
prediction of crack depth. scale of opposite plate will be aligned. So, as the crack
experiences movement (including shear or normal
4. DIFFERENT CRACK MEASURING DEVICES movement), one plate moves relative to other and the
FOR MONITORING CRACK WIDTH CHANGES variation can be measured to the closet of millimeters by
recording the position of the cursor with respect to the
There are varieties of crack measuring device available,
scale (Range ±20 mm – Resolution 1 mm).
which are used to measure crack width and change in
crack width. Crack width can be measured through visual
inspection within the specified range of the tool, while
change in crack width can be monitored using a fixed
gauge sensor to measure movement across surface cracks.
Some of the instruments used to monitor crack width
variations are as follows:
Figure 4: Details and Installation of Plastic Tell-Tale
• Crack Width Steel ruler
• Plastic tell-tale 4.3 GLASS TELL TALE
• Glass tell tale
• Displacement transducer Crack Monitor This technique used to measure crack width variation in
• Crack Width Microscope the past, but it is not popular any more. It basically
• 2-D pins and caliper consists of strip of glass cemented on to the cracked
• Vibrating Wire Crack Meter (Uniaxial) structural element as shown in Figure 5. As it may be
• 3-D Crack Meter (Mechanical Type) observed from the figure, glass tell-tale neither shows the
• Vibrating Wire Triaxial Crack Meter direction of the movement nor the magnitude of the
movement. That is why it is not used any longer.
4.1 CRACK WIDTH STEEL RULER
Steel ruler is simple instrument used to monitor crack
width variation. The width of the crack can be measured
to the nearest 0.5 mm provided that great care is
practiced. Steel rule measurements are subjective because
it is not possible to measure crack width from the same
point each time the measurement is taken. Steel ruler
measurements are used for assessing state of damage at
the beginning of investigation. Figure 3 describes
measurement of the crack through a steel ruler.
Figure 5: Glass Tell Tale
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International Journal of Engineering and Applied Sciences (IJEAS)
ISSN: 2394-3661, Volume-9, Issue-1, January 2022
4.4 DISPLACEMENT TRANSDUCER CRACK
MONITOR
This instrument is used to continuously monitor the
movement of cracks so as to provide warnings when
abrupt movement or in the case where the location of the
crack is not accessible like railway tunnel. Linear variable
displacement transformer (LVDTs) and potentiometric
displacement transducer are the two commonly devices
used to continuously monitor crack width variations. Both
instruments can be read either manually using hand held
unit or automatically employing data logger. This method
of monitoring crack width variation is expensive but the
requirement for such monitoring would justify the
Figure 7. Crack Width Microscope
utilization of these devices. Figure 6 shows a typical
example of installation of LVDT crack monitor.
4.6 2-D CRACK MONITOR
In this technique of monitoring crack width variation six
hexagonal stainless steel pins are fixed three on each side
of the crack as shown in Figure 8. Pin A and D are fixed
across the crack line and rests of pins are fixed both side
of pin A and D at 60◦ angle. The nomenclatures of pins
are clockwise from pin A. After that, a Vernier caliper is
used to measure the width of the crack as illustrated in
Figure 9. This crack monitor is used for monitoring of
crack movement in 2 directions viz. along the crack (X-
axis) i.e. the shear movement of the crack and across the
crack (Y-axis) i.e. the opening and closing of the
Figure 6: Installation of Linear variable displacement
crack/joint.
transformer instrument
4.5 CRACK WIDTH MICROSCOPE
The Crack Width Microscope is a small sized lightweight
and conveniently portable microscope to precisely
measure cracks in concrete and masonry construction
materials. The objective lens is positioned on the surface
over the crack and the knurled knob on the side is used to
sharpen the focus. The battery-powered lamp adjusts to
provide just the right amount of illumination, and the
eyepiece rotates 360° to align the optical measuring grid
with the crack. Figure 7 shows a typical crack width Figure 8: Fixing pins on each side of the crack
microscope.
With a magnification of 40 times this microscope can be
used to accurately measure the width of cracks and also
combines a calibrated focusing ring allow the depth of
cracks to also be accurately measured. 40 times image
magnification and measuring range of 1.6mm x 0.05 mm
ensure highly accurate measurements for a wide variety
of crack widths. The dual optical scale features coarse
divisions of 0.2 mm with fine graduations of 0.02 mm.
Figure 9: Measuring crack width using caliper
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International Journal of Engineering and Applied Sciences (IJEAS)
ISSN: 2394-3661, Volume-9, Issue-1, January 2022
4.7 VIBRATING WIRE CRACK METER
(UNIAXIAL)
The Vibrating Wire Crack Meter are used to measure
movement in structures along surface cracks or
construction joints. They consist of a sensor outer body
tube and an inner free sliding rod which is connected at
the internal end to a vibrating wire sensor by a spring as
shown in figure 10.
Figure 11: 3-D Crack Monitor
4.9: VIBRATING WIRE TRIAXIAL CRACK
METER
This is designed to monitor three way displacement at
joints and cracks. The design allows the Vibrating
Wire transducers to show independent movement in
Figure 10: Vibrating Wire Type Crack Meter
(Uniaxial) all directions, irrespective of each other. The crack
meter comprises a 3D mounting system which consists
If movement occurs within the structure causing the of two arms and two groutable anchors. Three
distance between the anchors on either side of the vibrating wire displacement transducers, which also
joint or crack to change, this change of distance will monitor temperature, are installed within the mounting
accurately be measured by the vibrating wire system and positioned for monitoring. Figure 12
transducer. Joint Meters/Crack Meters can also be shows diagram of a typical Vibrating Wire Triaxial
used to trigger an alarm if structural movement Crack Meter.
exceeds a pre-set maximum displacement.
4.8 3-D CRACK METER (MECHANICAL TYPE)
The 3-D crack monitor is capable of measuring crack
deformations in three mutually perpendicular directions
as shown in Fig. 11. X-axis measures the deformation
along the crack i.e. the shear movement of the crack. Y-
axis measures the deformation across the crack or
perpendicular to the crack. The opening and closing of
the crack/joint can be measured by Y-axis accurately. Z-
axis measures the relative deformation of the two walls
of the crack/joint perpendicular to X and Y-axes. Thus,
the deformations in all the three directions can be
measured with the help of the 3-D crack monitor. The
crack monitor can also be placed/fixed in any direction of
Figure 12: VW Triaxial Crack Meter
the crack and the deformations can be measured
accordingly. The crack monitor is lightweight, portable,
compact and is very easy to install. The dimensions of 5. CASE STUDY: RIHAND DAM PROJECT, U.P.
the instrument for measuring the deformation can be
Rihand Dam is a 92 m high, 934 m long concrete
changed suiting to the requirements at particular site.
gravity Dam was constructed during 1954-62 in the
district Mirzapur (now Sonebhadra) of Uttar Pradesh.
A powerhouse is located at the toe of the dam with an
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International Journal of Engineering and Applied Sciences (IJEAS)
ISSN: 2394-3661, Volume-9, Issue-1, January 2022
installed capacity of 300 MW. The dam consists of 61 6.0 CRACK MOVEMENT MONITORING BY USE
blocks of width ranging from 12.80 to 18.3 m with un- OF 2 D & 3D CRACK MONITORS
grouted joints. Block 1 to 27 and block 47 to 60
CSMRS, New Delhi took up instrumentation work for
constitutes to non-over flow portion. Block No. 28 to
crack movement monitoring in 1986. Long term
33 constitutes intake and powerhouse, while the
monitoring of crack movement is being done using
spillway is on blocks 34 to 46. The typical photograph
through 2D crack movement monitoring at 27 locations
of the dam is shown in Figure 13.
and using 3D crack monitors at 12 locations.
A reinforced concrete structure connects the toe of the
6.1 2-D CRACK MOVEMENT MONITORING &
dam with the Powerhouse, and has the floors at the DATA ANALYSIS
same levels as in powerhouse. The transformers are
placed on the top most floor of this framed structure. 2D pins were installed at 27 locations and regular
The load of the transformers is being transferred monitoring was done. Figure 14 show time dependent
directly to the dam toe through columns. The penstock data analysis of crack movement monitoring by
gallery is housed in this framed structure, which instrument (2D/10) installed between pillars no 5 and 6
separates the powerhouse structure through a 25 mm in powerhouse in October 1998. Data indicates that
joint. significant gradual movement in both directions. Since
its installation, there is gradual widening of crack and
Within a few years of commissioning of project in total gradual movement of 4.93 mm (across the crack)
1962, cracks began to appear in the various portions of and 3.24 mm (along the crack) has been observed till
the Dam and Appurtenant works. The expansion of March 2020. Over all monitoring data indicate cautious
concrete due to the alkali-aggregate reaction is leading approach needs to be exercised during dam monitoring
to cracking of concrete and consequently difficulty in and maintenance services.
operation of spillway gates, snapping of reinforcement
bars of the concrete column, smooth running of
Rihand Dam Project
turbine in the surface powerhouse at the downstream, 2D Crack Monitor
etc. It becomes, therefore, very important to monitor Location 2D/10 (EL: 622.0 ft.)
6.00 890.0
the cracks in the dam and appurtenant structures. 07.04.05&28.07.05: Readings of Across the crack could not
be taken due to missing of pins at point A & D 880.0
5.00
870.0
Relative Movement (mm)
4.00 860.0
Reservoir water level (ft.)
850.0
3.00
840.0
2.00 830.0
820.0
1.00 Across the crack
Along the crack 810.0
Reservoir water level (ft.)
0.00 800.0
10.10.98
13.10.99
31.05.00
22.08.01
09.05.02
24.07.03
20.05.04
28.07.05
18.12.07
23.09.10
19.12.12
05.03.14
31.01.18
18.03.20
Time (Date)
Figure 141: Plot of Relative Movement vs Time (Location
2D/10) i.e. 2-D Crack Movement Monitoring
Figure 13: Rihand Dam (Source: CSMRS (2020): Report on the Instrumentation
The case study deals with distress at Rihand Project Work for the Structural Behaviour Monitoring of Rihand
and implementation of instrumentation programme to Dam Project)
monitor the distress due to opening and closing of the 6.2: 3-D CRACK MOVEMENT MONITORING BY
joints/cracks. The cracks in the concrete and the 3-D CRACK MONITOR & DATA ANALYSIS
existing construction joints in the dam body and the Figure 15 shows data analysis of crack monitoring by
powerhouse are being monitored 2-dimensionally with instrument (3D/6) installed on column no 6 (D/S wall) in
2-D crack monitor and 3-dimensionally with 3-D power house in October 1998. Significant gradual
crack monitor for evaluating the remedial measures widening of crack in Y direction since its installation with
required in the dam and powerhouse of Rihand Dam total movement of 16.50 mm till March, 2020. However
gradual widening of crack in X and Z directions since its
Project in Uttar Pradesh, India.
installation with total movement of -3.53 mm and -2.93
mm till March, 2020. Over all monitoring data indicate
26 www.ijeas.org
International Journal of Engineering and Applied Sciences (IJEAS)
ISSN: 2394-3661, Volume-9, Issue-1, January 2022
cautious approach needs to be exercised during dam
monitoring and maintenance services.
Rihand Dam Project
3-D Crack Monitor Location:3D/6
( EL:622.0 ft.)
20.00
880.0
15.00
860.0
Reservoir Water Leel (ft.)
Relative Movement (mm)
10.00
840.0
5.00 X-Along the crack 820.0
Y-Across the crack
Z-Perp. to X&Y
Reservoir water level (ft.)
0.00 800.0
-5.00 780.0
13.01.00
26.04.01
05.09.02
19.09.03
19.10.04
20.06.07
22.09.10
06.03.13
28.07.16
18.03.20
10.10.98
Time(Date)
Figure 151: Plot of Relative Movement vs Time (Location
3D/6) i.e.3-D Crack Movement Monitoring
(Source: CSMRS (2020): Report on the Instrumentation
Work for the Structural Behaviour Monitoring of
Rihand Dam Project)
8. CONCLUSION
Cracks may appear in civil engineering structures, such as
buildings, the body of a dam, its galleries, adjoining
tunnels, and power plants during or after construction.
Swelling or poor soils in the foundations, redistribution of
stresses in the tunnels, creep of the materials, earthquakes
or other vibrations are just a few reasons for cracks. The
relative movements of the walls along and across the
crack, and perpendicular to the plane of cracking surface
or wall, beyond certain limits, may prove to be damaging.
For considerations of safety and maintenance, the
measurement of the magnitude and time rate of
deformation of the cracks is essential. Instrumentation for
deformation monitoring is of vital importance, especially
in underground excavations in complex geological
formations.
REFERENCES
[1] CSMRS (2020): Report on the Instrumentation Work for the
Structural Behaviour Monitoring of Rihand Dam Project (UP).
[2] Abdullah, Hasan, Verma S.K. and Dhawan A.K. (1998). Rihand
H.E. Project – A Case Study, National Seminar: Geotechnical Problems
– Case Studies, IGS Indore Chapter, 10th October, Indore.
[3] IS:456: 2000 (Reaffirmed 2005): Plain and Reinforced Concrete
Code of Practice
Rajkumar Prasad, Scientist ‘B’, Central Soil & Materials Research
Station, New Delhi.
Mahabir Dixit, Scientist ‘E’, Central Soil & Materials Research
Station, New Delhi.
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