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Consideration of degradation due to harsh environments, overweight vehicles, increasing traffic and frequent earthquake events are some of the challenges to overcome when designing reinforced concrete bridges. Structural elements can be affected by a reduction in strength and stiffness due to the carbonation of the concrete cover, the corrosion of the reinforcement, excessive cracking and displacement under service load and failure. Therefore, structures need to be monitored over time to ensure that they have the sufficient capacity to resist the intended design loads. The existing condition of bridges on toll roads and in ports located in Surabaya Indonesia has been investigated using non-destructive testing (NDT) equipment. Several reinforced concrete bridges of a high level of importance have been chosen as case studies considering different exposure and age of structure. Typical results from the site investigation are presented and discussed in this paper. The NDT equipment utilised in this paper includes the use of eddy current, two-chamber vacuum cell and Wenner Probe principle to assess the thickness, the air permeability and the electrical resistivity of the concrete cover, respectively. In addition, Silver Schmidt hammer was also used to measure the compressive strength of the concrete.
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13
1 INTRODUCTION
Under Joko Widodo-Jusuf Kalla presidency, the
Indonesian government has made a lot of efforts to
bring social justice from Sabang to Merauke (PWC
2017). One of them is to open up access for every
element of societies by developing new infrastruc-
tures and rehabilitating the old ones. To realise this,
Indonesia has budgeted 5% of its gross domestic
product (GDP) for Infrastructure (Alisjahbana
2012). In 2015, the total road network in Indonesia
is 488,181 km which consists of toll road of 976 km,
the national road of 47,017 km, the provincial road
of 47,666 km and district road of 392,521 km
(Directorate General Bina Marga 2016). By 2019, it
is expected that there will be additional toll road of
1000 km, the national road of 2650 km, provincial
and district road of 15,500 km. Moreover, there is a
lot of governmental support for assessment of the
ageing infrastructures to ensure that they can be used
safely for the intended service life. As part of the re-
pair works, 47,017 km of roads and bridge length of
446 km (in total) need to be repaired (Directorate
General Bina Marga 2016). There is obvious need
for fast and accurate assessment of infrastructure.
Three causes of bridges collapse are discussed in
this paper. They are corrosion (due to exposure),
overweight vehicle (live load) and higher earthquake
magnitude (natural disaster). Corrosion has become
one of the main reasons for ageing infrastructure es-
pecially in the marine environment which causes the
collapse of the structure (Chalhoub 2015). Both
chloride-induced corrosion and carbonation can re-
duce the strength and stiffness of the existing struc-
tures.
Increased weight of traffic can be another main
reason why the bridges can experience a reduced
service life. In Australia, the overall freight task
expressed in tonne-kilometer has had an annual
growth rate of over 50% in the past 35 years and the
average loads carried by articulated trucks have
more than doubled during this period (Mitchell
2010). In the USA, the overweight vehicle has
become the third cause of bridge collapse after
hydraulic events and collisions (Fiorillo and Ghosn
2017). People tend to ignore the weight limit of the
bridge and assume that the bridge has the capacity to
carry the imposed load. Chen (2013) stated that
based on the weigh-in-motion data, there is
approximately 24% of annual bridge cost in 2011 in
Use of Non-Destructive Methods: Case Studies of Marine Port and
Bridges Structures in Surabaya
Y. Oktavianus, M. Sofi*, E. Lumantarna, M. Maizuar, P.A. Mendis, C. Duffield &
A. Rajabifard
The University of Melbourne, Australia
H. Widyastuti
Institut Teknologi Sepuluh Nopember, Indonesia
*Corresponding Author: massoud@unimelb.edu.au
Keywords: Marine Ports, Bridge, Structure, Health Assessment
ABSTRACT: Consideration of degradation due to harsh environments, overweight vehicles, increasing traffic
and frequent earthquake events are some of the challenges to overcome when designing reinforced concrete
bridges. Structural elements can be affected by a reduction in strength and stiffness due to the carbonation of
the concrete cover, the corrosion of the reinforcement, excessive cracking and displacement under service
load and failure. Therefore, structures need to be monitored over time to ensure that they have the sufficient
capacity to resist the intended design loads. The existing condition of bridges on toll roads and in ports locat-
ed in Surabaya Indonesia has been investigated using non-destructive testing (NDT) equipment. Several rein-
forced concrete bridges of high level of importance have been chosen as case studies considering different
exposure and age of structure. Typical results from the site investigation are presented and discussed in this
paper. The NDT equipment utilised in this paper includes the use of eddy current, two-chamber vacuum cell
and Wenner Probe principle to assess the thickness, the air permeability and the electrical resistivity of the
concrete cover, respectively. In addition, Silver Schmidt hammer was also used to measure the compressive
strength of the concrete.
KEYWORDS: NDT, Structural Heath Assessment, Marine, Bridge, Indonesia
Special Issue: Electronic Journal of Structural Engineering 18(1) 2018
14
South Carolina allocated for maintenance and repair
work due to overweight trucks.
Natural hazards can cause extensive damage to
bridge structures. Indonesia, being located in the
ring of fire, is prone to earthquakes. Since 1966,
Indonesia has published its earthquake resistant
design standard. However, from 1966 to 2002,
Surabaya has the same design peak ground
acceleration (PGA) of 0.15g for rock soil with 500
years return period (Dewasa 2016). Indonesian
earthquake map has been updated in 2010 (SNI-
1726 2012) and 2017 (Menteri PUPR 2017) and
similar PGA of approximately 0.15-0.2g for rock
soil with 500 years return period earthquake has
been proposed. However, the last two updates have
followed AASHTO (2012) that bridges should be
designed for 1000 years return period (and not for
500 years return period). This corresponds to a PGA
value of 0.25-0.3g according to the latest standard
(Menteri PUPR 2017). While the design requirement
indicates an increase in the intensity of earthquakes ,
the capacity of existing structures remains the same
or even decreases due to deterioration. This could
lead to a massive damage to the existing RC bridge
structures, especially those built prior to 2012.
Both destructive testing and non-destructive test-
ing (NDT) methods can be used to assess the current
condition of the structures prior to the retrofitting
processes. However, the later has gained popularity
due to its ease and speed of application and cost-
effectiveness (IAEA-TCS-9 1999). In the past three
decades, there is a rapid development related to
NDT methods. The common NDT technique used
worldwide includes ultrasonic, radiographic, mag-
netic, electromagnetic, eddy-current, acoustic emis-
sion, half-cell potential measurement, Wenner probe
principle and hardness testing (ASTM C805 /
C805M 2013, ASTM C876 2015, Hellier 2013).
Related to the corrosion assessment of reinforced
concrete (RC) structures, previous researchers have
emphasised only one specific NDT equipment to
measure the corresponding parameter affecting
corrosion (AASHTO TP 95 2011, Andrade and
Alonso 2004, Andrade et al. 2009, ASTM C876
2015, Gu and Beaudoin 1998, Kucharczyková et al.
2010, Nakamura et al. 2008, Paulini and Nasution
2007, Salbei et al. 2014, Song and Saraswathy 2007,
Torrent 1992). Kucharczyková et al. (2010), Paulini
and Nasution (2007), Torrent (1992) have used a
two-chamber vacuum cell, so-called Torrent, for
measuring the coefficient of air permeability (kT) of
the concrete cover. The kT value can be used to
measure the required time to carbonate the concrete
cover, called initiation time (Kropp and Hilsdorf
1995). Other researchers used Wenner probe
principle to measure the electrical resistivity of the
concrete cover (AASHTO TP 95 2011, Andrade and
Alonso 2004, Andrade et al. 2009, Polder 2001).
The electrical resistivity is then converted to the
propagation time following the recommendation
from Andrade and Alonso (2004). To assess the
current corrosion state of the structures, half-cell
potential has been widely used (ASTM C876 2015,
Gu and Beaudoin 1998, Nakamura et al. 2008,
RILEM TC 154-EMC 2003). However, this requires
a direct access to the reinforcement within the
concrete, and hence, it is sometimes considered as a
destructive test.
Related to the strength assessment, hardness
testing using Silver Schmidt hammer is the most
common NDT method used to measure the concrete
compressive strength of the existing concrete
element. The existing structural conditions of
structures should be used to determine the structural
capacity in resisting the increased demand (from
vehicles or extreme events such as earthquakes).
A framework has been proposed in this paper to
assess the condition of existing critical infrastructure
considering various cases using several types of
NDT methods. This framework should provide in-
formation related to available equipment and proce-
dures to assess existing infrastructures. It should be
useful for the stakeholders and asset owners in prior-
itising inspection and future structural work includ-
ing repairing, retrofitting or replacing the structural
elements entirely.
Four RC bridges have been chosen as case studies
considering different exposure and age of the
structure. Two of those are the trestle RC bridges at
Terminal Peti Kemas and Terminal Teluk Lamong at
Port of Tanjung Perak Surabaya and the other two
are RC bridges at Toll Waru and Toll Sumo in Sura-
baya. The NDT equipment utilised in this paper in-
cludes Profometer (Proceq SA 2014) which uses ed-
dy current, Torrent (Proceq SA 1995) which uses
two-chamber vacuum cell and Resipod which uses
Wenner probe principle (Proceq SA 2016) to assess
the thickness, coefficient of the air permeability and
the electrical resistivity of the concrete cover, re-
spectively. In addition to that, Silver Schmidt ham-
mer was also used to measure the compressive
strength of the concrete. The results of the NDT
measurement including a brief discussion of the re-
sults are presented in this paper.
2 CASE STUDY
The location of two RC bridges at Port of Tanjung
Perak and two RC bridges at Tollway in Surabaya
which has been chosen as the case study is shown in
Figure 1. The first and second RC bridge at the
seaport of Tanjung Perak is shown as “TL” for
Teluk Lamong and “TPS” for Terminal Peti Kemas.
The first and second RC bridge at the tollway is
shown as Toll Sumo and Toll Waru. These bridges
are identified as typical critical infrastructures
around the port environment. The trestle bridges
connect the land and the berth and the toll road
15
bridges provide a transportation link between local
areas to wider Java area. The trestle bridges are
heavily used by trucks transporting goods to and
from the port. Failure of these bridges can cause a
significant economic loss to the country because
Port of Tanjung Perak is one of the busiest ports in
Indonesia.
A major difference between the bridges located at
the port and those at tollway is the environment. The
marine environment at the seaport can increase the
chloride-induced corrosion rate whereas the traffic
environment at tollway can increase the carbonation
rate. A brief overview of each bridge is described in
the following subsection.
Figure 1. Google earth of the location of four RC bridges
considered in this research
2.1 Longitudinal RC beams at the bridge in the
seaport of Tanjung Perak
The TPS bridge was built in 1984 and has 102 spans
with a length of 15 meters for each span (TPS 2013)
as shown in Figure 2. Each span is simply supported
on top of the cross beam through rubber bearing.
The cross beam is then supported by a group of steel
piles covered by anti-corrosion coating. The bridge
deck has an expansion joint every 20 spans to allow
the longitudinal movement of the bridge. The cross-
section of the bridge obtained from BGA (2010) is
shown in Figure 3.
Figure 2. View of the TPS bridge from the domestic
berth
The design compressive strength of the concrete
and the yield strength of the rebar is 40 MPa and
400 MPa, respectively. In 2010, the longitudinal T
beam has been repaired by grouting the cracks and
adding two concrete fibre reinforced polymer
(CFRP) Sika CarboDur type S10-12 along the
bottom of the beam (BGA 2010). The width and the
thickness of the CFRP are 100 and 1.2 mm,
respectively. The tensile strength and Young’s
modulus of the CFRP is 2800 and 165,000 MPa,
respectively.
(a)
(b)
Figure 3. TPS bridge: (a) Cross-section of the bridge looking
north; (b) The details for one longitudinal beam
The TL bridge has post-tensioned RC beams and
was built in 2010 as shown in Figure 4. The bridge
considered in this research has 20 spans with a
length of 40 meters for each span and it connects the
office of the Port of Teluk Lamong and the land in
Java Island Each. Each span consists of 5 precast
segments and is also simply supported on top of the
cross beam through rubber bearing. The cross beam
is then supported by a group of the spun pile with a
diameter of 800 mm and concrete grade of 58 MPa.
The cross-section of the I girder of the bridge at the
end and at the midspan is shown in Figure 5.
Figure 4. View of the TL bridge from the berth
The design compressive strength of the concrete
at jacking and at service is 46 MPa and 58 MPa,
respectively. The yield strength of the rebar is 390
MPa when the diameter is larger than 10 mm and
1000
4500
711 CHS
7080
4500
9 8 7 6 5 4 3 2 1
West East
7080
1560
200200
430
625
155
75
3D36
2x3D32
4D19
2x3D
2x11D
125 140
Surabaya
TPS
TL
Toll Waru
Toll Sumo
16
240 MPa when the diameter is smaller or equal to 10
mm. The thickness of the concrete cover is 40 mm at
top and bottom and 30 mm at the sides. There is no
repair or assessment that has been done since the
bridge is relatively new.
Figure 5. Cross-section of the I girder: (a) at both ends; (b) at
the midspan
2.2 RC columns at the bridge in Tollway
RC columns have been used as the case study in-
stead of the beam in the case of tollway due to the
difficulty in accessing the beam. There RC columns
in Pier-1 have been chosen at Toll Waru as shown in
Figure 6. The column has a height of 5.46, 5.68, and
5.9 metres from left to right, respectively. The three
columns are supporting 10 RC beams with a length
of 30 and 16 metres spanning from each side of the
column to the adjacent column. The cross-section of
the column is shown in Figure 7. The concrete com-
pressive strength of 29 MPa and steel yield strength
of 400 MPa was used in the design. The thickness of
the concrete cover is 70 mm.
Figure 6. RC bridge in Toll Waru with Pier-1 at the
left side of the picture
In toll Sumo, an exterior RC column from the
three columns in one pier has been chosen since
there was no access to the remaining columns as
shown in Figure 8. The column has a height of
4.31 metres. One pier (with three columns) supports
10 girders with a length of 30 metres which are
simply supported by the piers.
Figure 7. Cross-section of the RC column in Toll Waru: (a) All
columns half bottom; (b) All columns half top
Figure 8. RC bridge in Toll Sumo with the exterior column at
the right side of the picture
The concrete compressive strength of 29 MPa and
steel yield strength of 400 MPa was used in the de-
sign. The thickness of the concrete cover is 100 mm.
The column consists of two precast sections, i.e. half
bottom and half top as shown in Figure 9. Each of
the half sections has two different spacings of the
stirrups. The smaller spacing is used for the quarter
bottom of the column (Figure 9(a)) and quarter top
of the column (Figure 9(b)).
(a)
(b)
Figure 9. Cross-section of the exterior RC column in Toll Su-
mo: (a) All columns half bottom; (b) All columns half top
3 PROPOSED FRAMEWORK
Figure 10 shows the flowchart for the proposed
framework to assess the condition of the existing
RC structures. The steps are explained as follows:
(a)
(b)
(a)
(b)
Ø91
19 strands
15 strands
19 strands
19 strands
300300
2100
450
700
700
600
400300800
100
6D10
2D10
2D10
2D10
2D10
2D10
2D10
D13@200
D13@200
D10@200
2D10
1201280250250 70130
200
150
200
700
19 strands
19 strands 19 strands
15 strands
D13@200
2 D19@200
4 D19@200
1000
1200
100
100
D13@100
28 D32
1000
1200
100
100
D13@200
18 D32
2 D19@400
4 D19@400
D16@200/400
D16@200/400
42D32 D13@100/200 D13@100/200
30D32
36D32 D13@100/200
D16@200/400
D16@200/400
1600
1000
17
i. The as-built drawing should be obtained prior to
assessing the structure.
ii. Confirming specification using non-destructive
testing (NDT) equipment.
Profometer (Proceq SA 2014), which is based
on Eddy current, is used in this study to check
the thickness of the concrete cover and the ar-
rangement of the rebar. Moreover, concrete
compressive strength has been measured by us-
ing Silver Schmidt hammer (Proceq SA 2017)
which convert hardness to compressive strength
of concrete. The result is then compared with
the design values. Having the comparison be-
tween the as-built drawing and the results ob-
tained from the NDT, a conservative value may
be used for further steps.
Figure 10. The proposed framework to assess the condition of
the existing RC structures
iii. Measuring the carbonation and the corrosion
rate and predict the service-life due to the corro-
sion.
The service life of the structure due to the corro-
sion is defined by summing up the initiation
time and propagation time (Andrade et al.
2009). This service life is calculated based on an
assumption that there is neither excessive crack
nor concrete spalling during the life of the struc-
ture.
The initiation time is related to the carbonation
rate which can be obtained based on the coeffi-
cient of the air permeability of the concrete
cover (Kropp and Hilsdorf 1995). Torrent
(Proceq SA 1995) is used in this research to
measure the coefficient of air permeability of
the concrete cover. Moreover, the propagation
time is related to the corrosion rate which can
be calculated from the electrical resistivity of
the concrete cover (Andrade and Alonso 2004).
Resipod (Proceq SA 2016) which is based on
Wenner probe principle is used in this study to
measure the electrical resistivity of the concrete
cover. It should be noted that Torrent should be
used on a dry surface, whereas, Resipod should
be used on a wet surface.
Corrosion can be deemed to have occurred if
the initiation time measured by using Torrent is
less than the age of the corresponding structure,
causing reduction in the bar diameter. The re-
duced rebar diameter can reduce the capacity of
the structure and the structure may no longer
satisfy the serviceability and the ultimate limit
state. Moreover, if the predicted service life is
smaller than the expected, the structure may
need to be retrofitted.
iv. Measuring the current deflection and predict the
service-life based on the deflection over time.
Interferometric radar can be used to measure the
deflection as well as the natural frequency of
the structure at its current state (IDS 2012).
Comparing the current frequency with the one
obtained when the structure was newly con-
structed, the deterioration rate of the structure
can be measured. Moreover, considering the da-
ta obtained in the previous steps, the deflection
of the structure also can be determined by ana-
lytical method. If the predicted service life ob-
tained based on the deterioration rate is smaller
than the expected one, the structure needs to be
retrofitted.
v. Quantifying the capacity of the existing struc-
ture subjected to the current and future demand
(from vehicles or extreme events such as
earthquakes) in terms of probability.
The capacity of the existing structure is ana-
lysed based on the previously obtained data, i.e.
the reduced rebar diameter due to corrosion, the
actual measured concrete cover and the actual
measured concrete compressive strength. This
capacity is then compared to the current and fu-
ture demand. As stated previously that the
earthquake demand becomes higher in the re-
cent code, the capability of the structures in re-
sisting needs to be re-assessed. Moreover, the
new increased demand from overweight vehi-
cles should be also taken into account. The un-
certainties associated with the material proper-
ties and the demand can be considered in
developing fragility curves. When the probabil-
ity of the failure for a certain demand is higher
than the limit set either by the standard or by the
stakeholders, the structure needs to be strength-
ened.
4 RESULTS AND DISCUSSION
Due to the length limitation of the paper, this paper
only shows the results obtained from several types
Start: As-built drawing
Profometer: Cover thickness and rebar arrangement
Silver Schmidt hammer: Concrete compressive strength
Check and use
conservative value
Serviceability
limit
(deflection)
Ultimate limit
Current
demand New demand
Current
demand New demand
Carbonation
and chloride-
induced
corrosion
Predicted service life >
expected service life
Fragility curve:
Prob. Of Failure < limit
from the stakeholder
Retrofit
No need to
retrofit
YES NO
Retrofit
No need to
retrofit
YES NO
End
Predicted service life >
expected service life
Retrofit
No need to
retrofit
YES NO
18
of NDT equipment, i.e. Profometer, Silver Schmidt
hammer, Torrent and Resipod.
4.1 Longitudinal RC beam at TPS bridge
Since the TPS bridge is recently retrofitted (in
2010), it is expected that the thickness of the con-
crete cover remains the same. Therefore, profometer
was not used during the inspection. A concrete cover
of 75 mm to the main rebar was reported during the
retrofitting process (BGA 2010).
Table 1 shows the results obtained from hammer
test. The result obtained from each test is the aver-
age from 10 readings. The results are conservative
since it represents the 10th percentile value based on
the recommendation from ASTM C805 / C805M
(2013). The RC beams in span 90 were chosen as the
sample. Several locations have been selected, such
as the web and the flange of beam 1 and 2 and web
of beam 4, 7 and 8 (refer to Figure 3(a) for the loca-
tion of the beam). The average and the standard de-
viation for all the results is 51.7 and 9.6 MPa, re-
spectively. Based on these two results, the mean
value of 64 MPa was derived. However, both the
10th percentile and the mean value are higher than
the design compressive strength of 40 MPa.
Table 1. Readings obtained from Silver Schmidt hammer for
TPS bridge
______________________________________________
Location Concrete compressive strength (MPa)
Result 1 Result 2 Result 3
______________________________________________
Beam 1 web 51 50 42.5
Beam 1 flange 56 38.5 -
Beam 2 web 55.5 59 50
Beam 2 flange 48.5 52 -
Beam 4 web 57.5 63 -
Beam 7 web 56 - -
Beam 8 web 58.5 - -
_____________________________________________
Figure 11 shows the coefficient of the air perme-
ability (kT) obtained by using Torrent. The values on
the right vertical axis represent the quality of the
concrete cover on the air permeability. Very good
concrete cover is denoted as “1”. It is followed by
good (2), normal (3), bad (4) and very bad (5). Two
measurement locations have been chosen, i.e. at the
unpainted flange and at the painted web. Three read-
ings have been done for each location. The average
kT value for the unpainted flange and the painted
web is 12.310-6 m2 (very bad) and 0.62410-6 m2
(normal), respectively. It means that the painted sur-
face has better concrete cover quality than the un-
painted one.
Figure 12 shows the electrical resistivity of the
concrete cover obtained by using Resipod. The
higher the resistivity, the lower the corrosion rate as
shown in Table 2. From Figure 12, it is shown that
the measurement which was taken on the painted
web has higher resistivity value compared to that
taken on the unpainted flange. Again, the painted
surface provides a good advantage, i.e. increases the
electrical resistivity of the concrete cover. The
average resistivity value for the web and flange is
374.3 and 220.3 kcm, respectively. Moreover, the
standard deviation of 41.6 and 37.8 kcm is ob-
tained for the web and the flange, respectively. If a
conservative result is required, the value at 5% prob-
ability of exceedance needs to be calculated. It cor-
responds to 305.9 and 158.2 kcm for the web and
flange, respectively. Both the mean value and the
value at 5% of probability exceedance are much
higher than the limit for low corrosion rate. This
means that the quality of the concrete cover to pre-
vent the ingestion of the chloride to the reinforce-
ment is very good.
Figure 11. The coefficient of the air permeability for TPS
bridge
Figure 12. The electrical resistivity of the concrete cover for
TPS bridge
Table 2. Interpretation of the resistivity value.
________________________________________________
Risk of Resistivity (
) Corrosion rate Resistivity (
)
corrosion in kcm in kcm
________________________________________________
Negligible ≥ 100 Low ≥ 20
Low 50 to 100 Low to moderate 10 to 20
Moderate 10 to 50 High 5 to 10
High ≤ 10 Very high ≤ 5
________________________________________________
4.2 Longitudinal RC beam at TL bridge
As mentioned previously, TL bridge is quite new
(built in 2010) compared to the TPS bridge. This
means that the quality of the structure should be sim-
ilar to the as-built drawing. However, since there is a
good access to the I-girder, profometer is used to
confirm the location of the rebar and the thickness of
the concrete cover. The web of girder 2 span 3
(G2S3) was chosen as shown in Figure 13(a). The
0.001
0.01
0.1
1
10
100
123
kT values (10-16 m2)
Reading No.
Flange
Painted web
1
2
3
4
5
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16 18
Resistivity (kcm)
Measurement No.
Beam web Beam flange
Average
Average
19
result obtained from profometer by scanning the web
horizontally to observe the concrete cover and the
location of the stirrups is shown in Figure 13(b).
The average thickness of the concrete cover ob-
tained from Profometer is equal to 28.9 mm which is
very close to the value stated in the as-built drawing
which is 30 mm. Moreover, the spacing of the stir-
rups closer to the end of the beam segment is equal
to 105 mm which is also very similar to that in as-
built drawing which is 100 mm. However, the spac-
ing of the stirrups away from the segment end is
equal to 160 mm which is smaller than that in as-
built drawing which is 200 mm. The actual beam has
been built as specified on the as-built drawing with a
conservative value in the stirrups spacing in the
middle of the beam segment.
(a)
(b)
Figure 13. Profometer for longitudinal RC beam at TL bridge:
(a) Measured location and (b) Thickness of the concrete cover
Table 3 shows the results obtained from Silver
Schmidt hammer for TL bridge. As mentioned in
Section 4.1, the results obtained from the hammer
test represent the 10th percentile value. Having the
standard deviation of 7.1 MPa and average of the
10th percentile value of 51.3 MPa for all the results,
the mean value of 60.3 MPa has been derived. The
mean value is slightly higher than the design con-
crete compressive strength of 58 MPa as stated in
the as-built drawing.
Figure 15 shows the electrical resistivity for gird-
er G2S3 in TL bridge. The average value at the web
and at the flange is 80.2 and 42.4 kcm, respective-
ly. Moreover, the standard deviation of 20.4 and 5.6
kcm is obtained for the web and the flange, respec-
tively. The value at 5% probability of exceedance
corresponds to 46.8 and 33.1 kcm for the web and
flange, respectively.
Table 3. Test results obtained from Silver Schmidt hammer for
TL bridge
Test No.* Concrete compressive strength (MPa)
G2S3 G3S3 G4S3
Web Flange Web Flange Web Flange
__________________________________________ ______
1 56.5 67.5 38 56 48 59
2 55.5 57.5 42 49 46 52.5
3 - 60.5 38.5 51.5 42.5 -
Average 56 61.8 45.5 55.8 39.5 58.1
* Each test represents the average value of 10 readings
Figure 14 shows the coefficient of the air perme-
ability (kT) for the concrete cover of G2S3 obtained
by using Torrent. The average kT value for the web
is equal to 3.310-6 m2 (bad) and this is higher than
that for the flange which is equal to 0.6810-6 m2
(normal). This may be due to the higher compact-
ness of the concrete mix at the bottom of the girder
than that at the web.
Figure 14. The coefficient of the air permeability for TL bridge
Both the mean value and the value at 5% of prob-
ability exceedance are much higher than the limit for
low corrosion rate stated in Table 2. This means that
the quality of the concrete cover to prevent the in-
gestion of the chloride to the reinforcement is quite
good. However, the electrical resistivity at the bot-
tom flange is smaller than that of the web even the
thickness of the concrete cover at the bottom flange
is larger than that at the web. This is may be due to
the higher moisture content at the bottom flange of
the beam due to closer distance to the water surface.
Figure 15. The electrical resistivity of G2S3 in TL bridge
0.001
0.01
0.1
1
10
100
1 2 3
kT values (10-16 m2)
Reading No
Girder G2 web Girder G2 flange
1
2
3
4
5
0
20
40
60
80
100
120
140
0246810 12 14 16 18 20
Resistivity (kcm)
Measurement No.
G2S3 web G2S3 flange
Average
Average
20
4.3 RC columns at the bridge in Tollway
In this section, both the results obtained from Toll
Waru (TW) and Toll Sumo (TS) are discussed. Fig-
ure 16(a) shows the vertical scan obtained by using
profometer for an exterior column in TW. The
thickness of the concrete cover is equal to 48.8 mm
in average. This is smaller than the design value of
70 mm. Moreover, the average spacing of the stir-
rups is equal to 198 mm which is very similar to the
value stated in the as-built drawing which is 200
mm.
Figure 16(b) shows the vertical scan obtained by
using profometer for an exterior column in TS. The
thickness of the concrete cover is equal to 63.8 mm
in average. This is much smaller than the design
value of 100 mm. Moreover, the average spacing of
the stirrups is equal to 73 mm which is also much
smaller than the value stated in the as-built drawing
which is 200 mm at the measured location.
(a)
(b)
Figure 16. The concrete cover and rebar location measurement
using Profometer: (a) Vertical scan for exterior column in TW;
(b) Vertical scan for exterior column in TS
Table 4 shows the hammer test results for the RC
columns in both bridges. The design compressive
strength of the concrete for both locations is equal to
28.5 MPa. The average of 10th percentile value is
54.6 and 22.5 MPa for TW and TS, respectively.
The average standard deviation is 8 and 6.5 MPa for
TW and TS, respectively. Moreover, the mean value
is 64.9 and 30.8 MPa for TW and TS, respectively.
It means that all the mean compressive strength of
the RC column in both locations is higher than the
design strength. However, the mean compressive
strength of the RC column in TS has only a small
margin with the design value.
Figure 17 shows the coefficient of the air perme-
ability (kT) obtained by using Torrent for RC col-
umns at both locations. The average kT value for
TW (exterior), TW (interior), and TS (exterior) is
8.810-6 m2 (bad), 9.110-6 m2 (bad), and 34.510-6
m2 (very bad), respectively. It can be seen that the
lower the concrete compressive strength, the higher
the kT value. The higher kT value indicates that there
is more water content in the concrete mix which
leads to more porosity when the concrete is set.
Table 4. Test results obtained from Silver Schmidt hammer for
RC column in Tollway
Test No.* Concrete compressive strength (MPa)
TW_Ext TW_Int TS_Ext_bot TS_Ext_top
1 60 50 16 30.5
2 60 48.5 16.5 22
3 - - - 29
4 - - - 21
Average 60 49.3 16.3 25.6
* Each test represents the average value of 10 readings
Figure 18 shows the electrical resistivity for the
RC columns in both locations. The average resistivi-
ty for TW (exterior), TW (interior), and TS (exteri-
or) is 136.2, 100.2, and 46.76 kcm, respectively.
The corresponding standard deviation is 20.5, 15,
and 4.8 kcm. The value at 5% probability of ex-
ceedance corresponds to 102.5, 75.7, and 38.8 kcm
for TW (exterior), TW (interior), and TS (exterior),
respectively.
A similar conclusion can be made for this speci-
men that since both the mean value and the value at
5% of probability exceedance are much higher than
the limit for low corrosion rate stated in Table 2, the
concrete cover has a good resistivity to prevent the
ingestion of the chloride to the reinforcement. The
electrical resistivity of the specimen in TS is smaller
than that in TW. This is because of much smaller
concrete compressive strength of the specimen. If
the thickness of the concrete cover in TS is the same
as in TW, it is expected that the resistivity for RC
column in TS will be even smaller.
Figure 17. The coefficient of the air permeability for the bridge
in Tollway
0.001
0.01
0.1
1
10
100
1 2 3
kT values (10-16 m2)
Reading No
TW_Exterior Column
TW_Interior Column
TS_Exterior Column
1
2
3
4
5
21
Figure 18. The electrical resistivity for the bridge in Tollway
4.4 Further discussion
The data obtained from the as-built drawing and ob-
tained during the investigation is very useful for fur-
ther assessment of the bridge. The structure can be
modelled based on the precise information taking in-
to account the probability of the material properties
obtained from the NDT observation. The corrosion
should be checked prior to the analysis of the struc-
ture to enhance the accuracy of the size of the rein-
forcement, in case if corrosion is present. At last,
retrofit should be recommended if the structure does
not satisfy the expected/required limit.
5 CONCLUSIONS
This paper has proposed a framework on how to as-
sess the condition of existing reinforced concrete
(RC) structures. The proposed framework involves
the use of multiple types of NDT equipment to en-
hance the accuracy of the structure including the
standard deviation of the material properties. Corro-
sion, deflection, and strength of the existing struc-
tures should be checked thoroughly.
Two RC bridges in Port of Tanjung Perak and
Two RC bridges in Tollway in Surabaya has been
chosen as the case study. Moreover, different expo-
sure and age of the structure have also been consid-
ered. Due to the length limitation of the paper, this
research focused only on the results of the NDT ob-
servation which are very useful for the analysis
steps.
From the NDT observation, several key conclu-
sions have been made as follows:
1. The data obtained from the as-built drawing
needs to be checked using NDT equipment to
confirm the accuracy of the drawing (especially
the thickness of the concrete cover, bar ar-
rangement, and the concrete compressive
strength). It has been found that some of the
reading is different to the information provided
in the as-built drawing. This update is crucial
for the analysis steps to assess the actual capaci-
ty of the structure.
2. The coefficient of the air permeability of the
painted surface is smaller than that of the un-
painted one. It means that the initiation time of
the corrosion is longer for the painted surface
than for the unpainted one.
3. In general, there is a low corrosion rate for all
the structural elements investigated in this paper
since the electrical resistivity is higher than 20
kcm. This is due to the high importance and
the exposure of the structure which made the
concrete cover to be quite thick.
ACKNOWLEDGEMENT
The authors would like to thank Australia Indonesia
Centre (AIC) for funding Strategic Research Project
2. The contribution from the Australian Research
Council’s Discovery Early Career Researcher Grant
(DE170100165, DE 2017 R1) is acknowledged. The
equipment was purchased through an ARC LIEF
Grant (LE140100053).
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