materials

Article
Experimental Study on Shear Capacity of Reinforced
Concrete Beams with Corroded
Longitudinal Reinforcement
Sun-Jin Han 1 , Hyo-Eun Joo 1 , Seung-Ho Choi 1 , Inwook Heo 1 , Kang Su Kim 1, *
and Soo-Yeon Seo 2
1 Department of Architectural Engineering, University of Seoul, 163 Seoulsiripdaero, Dongdaemun-gu,
Seoul 02504, Korea; sjhan1219@gmail.com (S.-J.H.); joo8766@uos.ac.kr (H.-E.J.);
ssarmilmil@gmail.com (S.-H.C.); inwookheo@gmail.com (I.H.)
2 Department of Architectural Engineering, Korea National University of Transportation, 50 Daehak-ro,
Geomdan-ri, Daesowon-myeon, Chungju-si, Chungcheongbuk-do 27469, Korea; syseo@ut.ac.kr
* Correspondence: kangkim@uos.ac.kr




Received: 15 February 2019; Accepted: 8 March 2019; Published: 12 March 2019


Abstract: In this study, shear tests were conducted to investigate the effects of longitudinal reinforcement
corrosion on the shear capacity of reinforced concrete (RC) members with transverse reinforcement.
To this end, a total of eight test specimens were fabricated, and the corrosion rates and anchorage
details of rebars were set as test variables. In addition, an accelerated corrosion technique was used
to introduce corrosion into the longitudinal reinforcement without corroding shear reinforcement.
The test results indicated that the capacities of the specimens in which tension reinforcement was not
properly anchored at the ends of the members decreased rapidly at high corrosion rates, whereas the
capacities of the specimens in which tension reinforcement was properly anchored by hooks were
similar to or higher than those of the non-corroded specimens, despite bond loss caused by corrosion.

Keywords: corrosion; reinforced concrete; shear behavior; bond performance; anchorage

1. Introduction
In reinforced concrete (RC) structures, reinforcement corrosion is prevented by the strong
alkalinity of the concrete cover surrounding the reinforcement [1,2]. However, if carbon dioxide
in the atmosphere results in the carbonation of the concrete cover, or if chloride attacks destroy the
passive films on the steel reinforcement, corrosion of reinforcement begins, and then the effective
sectional area of reinforcement and the bond performance between the reinforcement and concrete
drastically decrease [1–3]. In this regard, many studies have been conducted on the correlation between
the bond performance of reinforcement changed by corrosion and the flexural performance of RC
members [4–13], and several analysis models have been developed so far. Al-Sulaimani et al. [8] and
Azad et al. [9] conducted accelerated corrosion tests on tensile reinforcement, and evaluated flexural
performance of RC beams with corroded longitudinal tensile reinforcement. Based on the test results,
they reported that the flexural strength is reduced by the loss of sectional area of tensile reinforcement
at the early stages of corrosion and that the bond failure occurs when the corrosion rate exceeds the
critical corrosion rate. Maaddawy et al. [13] carried out an analytical research on flexural behavior of
corroded RC members based on bond-slip relationships between corroded reinforcement and concrete,
and verified their proposed model by comparing with their test results. In addition, Han et al. [5]
suggested a bond failure criterion for the RC members with corroded longitudinal reinforcement.
However, there has been relatively little research on the effects of reinforcement corrosion on
the shear capacities of RC members. Higgins and Farrow [14] and Zhao et al. [15] reported that the

Materials 2019, 12, 837; doi:10.3390/ma12050837 www.mdpi.com/journal/materials

Materials 2019, 12, 837 2 of 19

corrosion in shear reinforcement reduces the shear strength of the RC members. This is caused by a
drastic decrease in the sectional area of the stirrups due to pitting corrosion rather than by a decrease
in the bond performance between the corroded reinforcement and concrete. EI-Sayed [16] proposed
shear strength estimation methods for slender and deep RC beams with corroded stirrups that reflect
the loss of sectional area of stirrups and the decrease in effective compressive strength of concrete due
to cracks by corrosion.
However, the shear resistance mechanism of the RC members, which is changed by the corrosion
of the longitudinal tension reinforcement, has been shown to be more affected by a decrease in
bond performance between the reinforcement and concrete than a reduction in the sectional area of
reinforcement [17–21]. Azam and Soudki [17,18] reported that the shear capacities of RC members
with corroded longitudinal tension reinforcement can be enhanced by about two times the shear
capacity of non-corroded RC members due to development of arch action. On the other hand, Jeppsson
and Thelandersson [19] mentioned that the shear capacity of corroded RC members decreases as the
corrosion rate of longitudinal reinforcement increases, which is caused by the bond loss between
corroded reinforcement and surrounding concrete. Xue and Seki [22] reported that the effect of
corrosion of longitudinal reinforcement on shear capacity of RC members varies depending on the
shear span to depth ratio (a/ds ). In their test, the shear capacity of corroded RC specimens with
a/ds = 2.6 increased by two times compared with the non-corroded RC specimen, while in the
case of corroded RC specimens with a/ds = 4.0, the shear capacity decreased as the corrosion rate
of longitudinal reinforcement increased. Although there have been experimental researches on the
shear capacity of RC members with corroded longitudinal reinforcement, their research findings are
somewhat conflicted, and, thus, the relationship between corrosion of tensile reinforcement and shear
capacity of RC member still requires further investigation.
Therefore, in this study, shear tests were conducted to examine the shear capacities of RC
members with corroded longitudinal reinforcement. For the test, a total of eight RC specimens
with transverse reinforcement were fabricated, in which the level of corrosion (ωcorr = 0%, 3%, 8%,
and 15%) and anchorage type (straight or hooked) were set as the main variables. To closely examine
the effects of corrosion occurring in longitudinal reinforcement on the shear capacities of RC members,
the accelerated corrosion technique was used so as to introduce corrosion into the longitudinal
reinforcement without any corrosion of the shear reinforcement. Strain gauges were attached to the
shear reinforcements of all specimens to measure the strains of transverse reinforcement, and the
shear strain distributions of the concrete web were measured using an image-based displacement
measurement system [23,24]. In addition, the crack patterns, failure modes, and shear responses of the
specimens were analyzed in detail according to the corrosion rate in longitudinal reinforcement.

2. Experimental Program

2.1. Test Specimens

Table 1 and Figure 1 show the details and material properties of the test specimens, where the
test groups are divided into the TS and TH series, respectively. As shown in Figure 1, the longitudinal
tension reinforcement of the TS series specimens was anchored with a straight type end, while that
of the TH series specimens was anchored with a 90-degree hooked type end. The test specimens of
each test group were designed to have four target corrosion rates (ωcorr = 0%, 3%, 8%, and 15%).
The widths (bw ), heights (h), and lengths (L) of all specimens were 170 mm, 250 mm, and 1400 mm,
respectively. Two rebars with a diameter of 22 mm were placed on the tension side. To induce shear
failure of the member, high strength steel bars with a yield strength of 635 MPa were used for tension
reinforcement. In addition, 10 mm diameter shear reinforcements were placed at 100 mm intervals
to satisfy the minimum shear reinforcement ratio specified in the ACI 318-14 building code [25], and
strain gauges were attached to the shear reinforcement. Since this study aimed to investigate the
effects of longitudinal reinforcement corrosion on the shear capacity of RC members with transverse
 Materials 2019, 12, x FOR PEER REVIEW 3 of 19

effects of longitudinal reinforcement corrosion on the shear capacity of RC members with transverse
reinforcement, epoxy coated steel bars were used for shear reinforcement to prevent corriosion, and
their yield
Materials strength
2019, 12, 837 was 534 MPa. Meanwhile, for the accelerated corrosion test shown in the 3 of 19
following section, 10 mm diameter stainless steel bars were placed inside the test specimens,
excluding the reference specimens (TS-0 and TH-0), so that they did not come into contact with the
reinforcement, epoxy coated
tension reinforcement. steel bars
The specimens were
were used to
subjected forsteam
shearcuring
reinforcement to the
for 24 h after prevent corriosion,
placement of
and their yield strength was 534 MPa. Meanwhile, for the accelerated corrosion
concrete, then underwent atmospheric curing until the age of 28 days. Finally, the accelerated test shown in the
following
corrosionsection,
test was 10performed
mm diameter stainless
on the steel bars
specimens. Thewere placed inside
compressive the of
strength testconcrete
specimens,( f c'excluding
) was
the reference specimens (TS-0 and TH-0), so that they did not come into contact with the tension
found to be 56.3 MPa at the time of the shear test.
reinforcement. The specimens were subjected to steam curing for 24 h after the placement of concrete,
then underwent atmospheric Tablecuring until
1. Details andthe age ofproperties
material 28 days.ofFinally, the accelerated corrosion test was
test specimens.
performed on the specimens. The compressive strength of concrete ( f c 0 ) was found to be 56.3 MPa at
the time of the shear bw test. h ds As Av sv C fc‘ fy fvy ωcorr
Specimens a/ds
2 2
(mm) (mm) (mm) (mm ) (mm ) (mm) (mm) (MPa) (MPa) (MPa) (%)
Table 1. Details and material properties of test specimens.
TS-0 / TH-0* 0
TS-3 / TH-3* bw h ds As Av sv C fc 0 fy fvy 3
ωcorr
Specimens 170 250 210 845.5 71.3
2 ) (mm 100 (mm)
2 ) (mm) 30 635 (MPa)534a/ds2.86 (%)
56.3 (MPa)
(mm) (mm) (mm) (mm (MPa)
TS-8 / TH-8* 8
TS-0/TH-0 * 0
TS-15 / TH-15* 15
TS-3/TH-3 * 170 bars
250in TH210 845.5 71.3 100 properly
30 anchored
56.3 635hooks.
534 2.86 3
*Note: Reinforcing series specimens have been by **Notations:
TS-8/TH-8 * h = beam height (mm); 8
f c′ = compressive strength of concrete (MPa); bw = web width (mm);
TS-15/TH-15 * 15
ds = effective depth of reinforcement (mm); As = sectional area of non-corroded tension
* Note: Reinforcing bars in TH series specimens have been properly anchored by hooks. ** Notations: f 0 =
reinforcement (mm2); Av = sectional area of stirrup (mm2); f y = yield strength of tensionc
compressive strength of concrete (MPa); bw = web width (mm); h = beam height (mm); ds = effective depth of
reinforcement
reinforcement (mm);
(MPa); = yieldarea
As =f vysectional of non-corroded
strength tension
of transverse reinforcement
reinforcement (mms2v);=Avstirrup
(MPa); = sectional area of
spacing
stirrup (mm2 ); f y = yield strength of tension reinforcement (MPa); f vy = yield strength of transverse reinforcement
(MPa); ==
(mm);sv C coverspacing
stirrup thickness
(mm); of C
concrete; a / ds = shear
= cover thickness span to
of concrete; a/ddepth ratio.
s = shear span to depth ratio.

ϕ10 stainless steel

TS series specimens A Section A-A
D10 epoxy coated steel bar
ϕ10 stainless steel
D22 steel bar

A
D10 epoxy coated steel bar D22 steel bar (high strength steel)
@100
Strain gage attacked at stirrup

(a)
TH series specimens ϕ10 stainless steel
A Section A-A
D10 epoxy coated steel bar
ϕ10 stainless steel
D22 steel bar

D10 epoxy coated steel bar D22 steel bar (high strength steel)
@100
Strain gage attacked at stirrup

(b)
Figure1.1.Details
Figure Details of
of test specimens
specimens(Unit:
(Unit:mm).
mm).(a)
(a)TSTSseries specimens;
series (b)(b)
specimens; THTH
series specimens.
series specimens.

2.2.
2.2.Accelerated
AcceleratedCorrosion
Corrosion Technique
Technique
Figure 2 shows a schematic description of the accelerated corrosion test. After the age of 28 days,
the specimens were precipitated in a 5% NaCl solution, and then dried in air for a week. After the
wetting-drying cycle, the specimens were precipitated again in the 5% NaCl solution, and a constant
current was provided by connecting the steel bar and stainless steel to direct current (D.C.) power
supply with 5.0 A capacity so that the D22 tensile reinforcement could act as the anode and the D10
stainless steel could act as the cathode. Andrade et al. [26] and Al-Harthy et al. [27] reported that
the current density (icorr ) measured in actual RC structures is less than 0.1 µA/cm2 , but previous
current was provided by connecting the steel bar and stainless steel to direct current (D.C.) power
supply with 5.0 A capacity so that the D22 tensile reinforcement could act as the anode and the D10
stainless steel could act as the cathode. Andrade et al. [26] and Al-Harthy et al. [27] reported that the
current density ( icorr ) measured in actual RC structures is less than 0.1 μA/cm2 , but previous
Materials 2019, 12,
researchers used837 current densities ranging from 150 μA/cm 2 to 10,400 μA/cm2 in 4 of
the19

accelerated corrosion test [28]. Lin and Zhao [29] reported that a difference between the corrosion
current density
researchers usedincurrent
the natural environment
densities and 150
ranging from thatµA/cm
in the 2laboratory environment
to 10, 400 µA/cm 2 in thecan cause a
accelerated
difference in the type of corrosion products formed on the reinforcement surface as well as the
corrosion test [28]. Lin and Zhao [29] reported that a difference between the corrosion current density
amount of corrosion.
in the natural They also
environment noted
and that in that it is desirable
the laboratory to use ascan
environment small a iacorrdifference
cause value asinpossible.
the type
of corrosion products formed on the reinforcement surface as well as the amount
However, as a lower current density is used, more time is required to achieve the target corrosion of corrosion. They
also noted that it is desirable to use as small a
rate, thus, making it difficult to derive research results i value as possible. However, as a lower
corr in a limited research project period. Therefore, current
density is used, more time is required to 2
achieve theon
target corrosion rate,[28].
thus,Themaking it difficult to
in this study, icorr was set to 1000 μA/cm based previous research time set to obtain
derive research results in a limited research project period. Therefore, in this study, icorr was set to
the target
1000 µA/cmcorrosion
2 based rate ωcorr ) was
on (previous estimated
research [28].based on Faraday’s
The time law [28],
set to obtain and the
the target times ( t rate
corrosion ) required
(ωcorr )
was
to estimated
obtain based
the target on Faraday’s
corrosion ωcorr[28],
rates (law ) of and
3%, the
8%, times (t) required
and 15% to obtain
were calculated asthe target
5, 14, andcorrosion
26 days,
rates (ωcorr ) of 3%, 8%, and 15% were calculated as 5, 14, and 26 days, respectively.
respectively.

Figure 2. Schematic description of accelerated corrosion test.

Figure 2. Schematic description of accelerated corrosion test.
Upon completion of the shear test, the corroded reinforcement was separated from the specimen
Upon completion
so as to measure of the shear
the actual test, the
corrosion ratecorroded reinforcement
of the longitudinal was separatedAll
reinforcement. from
of the
the specimen
corrosion
so as to measure
products around the tension
actual corrosion rate ofwere
reinforcement the dissolved
longitudinal reinforcement.
using All of
Clark’s solution the corrosion
presented in the
products around the tension reinforcement were dissolved using Clark’s solution presented
ASTM standard G1 [30], and the weight was measured using electronic scales. The actual corrosion in the
ASTM
rate of standard G1 [30], and
the test specimens canthe weight wasasmeasured
be calculated follows. using electronic scales. The actual corrosion
rate of the test specimens can be calculated as follows.
m0 − m
ωcorr = m0 − m11 × 100% (1)
ω corr = m0 × 100% (1)
m0
where m
where m00 isisthe
theinitial
initialweight
weight of longitudinal reinforcement,
of longitudinal reinforcement,and m1 isis the
and m the weight of longitudinal
weight of longitudinal
1
reinforcement after removing all of the corrosion products.
reinforcement after removing all of the corrosion products.
2.3. Shear Test Set-Up
2.3. Shear Test Set-Up
Figure 3 shows the test setups for the shear test. The shear span (a) was constant for all specimens
Figure
at 600 3 shows
mm, and thespan
the shear test to
setups
depthfor the
ratio shear
(a/d test. The shear span ( a ) was constant for all
s ) was 2.86. As shown in Figure 3a, the specimens were
specimens
subjected toatone-point
600 mm, and the shear
loading at thespan
centertoof
depth ( a / the
ratio and
the span, ds )mid-span
was 2.86. deflections
As shown in of Figure 3a, the
the specimens
were measured
specimens using a linear
were subjected variable
to one-point differential
loading at the transformer (LVDT)
center of the span, andinstalled on thedeflections
the mid-span bottom of
the section located at the loading point. In addition, an image-based displacement
of the specimens were measured using a linear variable differential transformer (LVDT) installed on measurement
system
the [23,24]
bottom wassection
of the used to measure
located the loading
at the shear strain distribution
point. of an
In addition, the image-based
concrete web,displacement
as shown in
Figure 3b.
Materials 2019, 12, x FOR PEER REVIEW 5 of 19

measurement
Materials 2019, 12, system
[23,24] was used to measure the shear strain distribution of the concrete 5web,
837 of 19
as shown in Figure 3b.

(a)

(b)
3. Shear
Figure 3. Shear test set-up. (a)
(a) Test Image-based displacement
Test set-up for one-point loading; (b) Image-based displacement
measurement system.

3. Experimental Results
3. Experimental Results

3.1. Accelerated Corrosion Test Results

3.1. Accelerated Corrosion Test Results
Table 2 and Figure 4 show summaries of the corrosion rates of longitudinal steel reinforcement as
Table 2 and Figure 4 show summaries of the corrosion rates of longitudinal steel reinforcement
calculated using Equation (1). While the target corrosion rates of the specimens were 3%, 8%, and 15%,
as calculated using Equation (1). While the target corrosion rates of the specimens were 3%, 8%, and
the measured corrosion rates were 1.14%, 4.13%, and 9.76% in the TS-3, TS-8, and TS-15 specimens,
15%, the measured corrosion rates were 1.14%, 4.13%, and 9.76% in the TS-3, TS-8, and TS-15
respectively, and 1.64%, 4.64%, and 8.82% in the TH-3, TH-8, and TH-15 specimens, respectively.
specimens, respectively, and 1.64%, 4.64%, and 8.82% in the TH-3, TH-8, and TH-15 specimens,
The reason for why the actual corrosion rates of the specimens are smaller than the target corrosion
respectively. The reason for why the actual corrosion rates of the specimens are smaller than the
rates is as follows. As the corrosion of reinforcement progresses, the corrosion product surrounds
target corrosion rates is as follows. As the corrosion of reinforcement progresses, the corrosion
the reinforcement, thus, interfering with the supply of oxygen (O2 ) and water (H2 O) needed to form
product surrounds the reinforcement, thus, interfering with the supply of oxygen (O2) and water
corrosion cells. In addition, as mentioned above, it is estimated that the magnitude of corrosion current
(H2O) needed to form corrosion cells. In addition, as mentioned above, it is estimated that the
density (icorr = 1000 µA/cm2 ) used in the accelerated corrosion test is considerably large, which leads
magnitude of corrosion current density ( icorr = 1000 μA/cm 2 ) used in the accelerated corrosion test
to a difference between the corrosion rate calculated from Faraday’s law and the actual corrosion rate.
is considerably
Therefore, large,
to obtain the which leads to rate,
target corrosion a difference between
it is desirable the corrosion
to perform rate calculated
the accelerated corrosionfrom
test
Faraday’s law and the actual corrosion rate. Therefore, to obtain the target corrosion rate, it is
Materials 2019, 12, x FOR PEER REVIEW 6 of 19
Materials 2019, 12, 837 6 of 19
desirable to perform the accelerated corrosion test using the current density range
2 2
( 150 μA/cm ~400 μA/cm ) as that used by Azam and Soudki [17,18] and Lin and Zhao [29].
using the current density range (150 µA/cm2 ∼ 400 µA/cm2 ) as that used by Azam and Soudki [17,18]
and Lin and Zhao [29].
Table 2. Measured corrosion rates of test specimens.
Table 2. Measured corrosion rates of test specimens.
Before Corrosion (g) After Corrosion (g) Mass Loss (g) Corrosion Rate (%)
Specimen
Specimen
Bar 1 Corrosion
Before Bar(g)2 AfterBar 1
Corrosion (g) Bar 2Mass Loss
Bar(g)
1 Bar 2 Corrosion
Bar 1 Rate
Bar 2(%)Average
TS-3 3803.9
Bar 1 3785.3
Bar 2 Bar 3759.7
1 Bar 2 3742.7
Bar 1 44.2
Bar 2 42.6
Bar 1 1.16Bar 21.13 Average
1.14
TS-8 TS-3 3809.1
3803.9 3847.1 3759.7
3785.3 3689.13742.7 3650.5 44.2 120.0
42.6 196.61.16 3.151.135.11 1.144.13
TS-15TS-8 3809.1
3856.3 3847.1
3782.7 3689.1 3406.93650.5 3485.0120.0 196.6
449.4 297.73.15
11.655.117.87 4.139.76
TS-15 3856.3 3782.7 3406.9 3485.0 449.4 297.7 11.65 7.87 9.76
TH-3TH-3 4619.9 4619.9 4644.6 4540.4
4644.6 4540.44572.5 4572.5 79.5 79.5
72.1 72.1 1.72 1.721.551.55 1.641.64
TH-8TH-8 4631.6 4631.6 4749.9
4749.9 4462.9 4462.94481.8 4481.8168.7 168.7
268.1 268.13.64 3.645.645.64 4.644.64
TH-15 4750.9 4734.6 4357.6 4291.8 393.3 442.8 8.28 9.35 8.82
TH-15 4750.9 4734.6 4357.6 4291.8 393.3 442.8 8.28 9.35 8.82

(a)

(b)
Figure 4.
Figure Accelerated corrosion
4. Accelerated corrosion test
test results.
results. (a)
(a) Corroded
Corroded longitudinal
longitudinal reinforcement
reinforcement extracted
extracted from
from
test specimens;
test specimens; (b)
(b) Target
Target and measured corrosion rates of test specimens.

Figure 55 shows
Figure shows the
the crack
crack patterns
patternsinduced
inducedbybylongitudinal
longitudinalreinforcement
reinforcementcorrosion.
corrosion.According
According to
previous
to previous studies
studies[8,31],
[8,31],the
theconcrete
concretecover
covercracks
cracksoccur
occurininthe
thecorrosion
corrosion rate
rate range
range ofof about
about 11to
to3%,
3%,
which is the so called corrosion crack. In addition, as the corrosion progresses, the bond
which is the so called corrosion crack. In addition, as the corrosion progresses, the bond performance performance
between reinforcement
between reinforcement and and concrete
concrete decreases
decreases sharply
sharply with
with increasing
increasing widths
widths of
of the
the corrosion
corrosion cracks.
cracks.
In the TS-3 and TH-3 specimens ( ωcorr = 1.14% and 1.64%, respectively) with a target corrosion rate
In the TS-3 and TH-3 specimens (ωcorr = 1.14% and 1.64%, respectively) with a target corrosion rate
of 3%, only small crack widths of less than 0.05 mm were measured. However, in the TS-8 and TH-8
of 3%, only (ω
specimens small =crack
4.13%widths of lessrespectively),
and 4.64%, than 0.05 mmcrack
werewidths
measured. However,
of more than 0.5inmmthe were
TS-8 and TH-8
measured
corr
specimens ( ωcorr = 4.13%
along the longitudinal and 4.64%, respectively),
reinforcement crackserious
layers, and more widths damages
of more than 0.5 concrete
to the mm werecover
measured
were
observed from the TS-15 and TH-15 specimens
along the longitudinal reinforcement layers, and more (ω = 9.76% and 8.82%, respectively), whose
corr serious damages to the concrete cover were crack
widths were up to 6.0 mm or more.
Materials 2019, 12, x FOR PEER REVIEW 7 of 19

Materials
observed 2019, 12, 837
from the TS-15 and TH-15 specimens ( ωcorr = 9.76% and 8.82%, respectively), whose 7crack
of 19

widths were up to 6.0 mm or more.

Left side TS-3 Specimen (Unit: mm) Left side TH-3 Specimen (Unit: mm)

0.05 0.05 0.05 0.05 0.05

Bottom surface Bottom surface

0.05
0.05 0.05 0.05 0.05
0.05

Right side Right side

0.05 0.05 0.05

(a)
Left side TS-8 Specimen (Unit: mm) Left side TH-8 Specimen (Unit: mm)

0.5
0.5
1.0 0.5 0.7 3.0 2.0
1.0

Bottom surface Bottom surface

0.4 0.5 0.2 0.05 0.05 0.05
0.2 0.05 2.0
0.05 0.5
Right side Right side

0.1
0.1
0.5
0.6

(b)
Left side TS-15 Specimen (Unit: mm) Left side TH-15 Specimen (Unit: mm)

0.5 0.05
1.0 5.0 3.0 2.0 5.0 3.0

Bottom surface Bottom surface

0.5 1.0
0.1 1.5 0.05
0.1 0.1 0.1

Right side Right side

0.1 0.5 1.5 0.1

0.5
1.7 6.0 2.0 1.5 1.5 4.0

(c)
Figure 5.
Figure 5. Crack patterns induced by corrosion in longitudinal reinforcement.
reinforcement. (a) Target
Target corrosion
corrosion rate
rate
of 3%;
of 3%; (b)
(b) Target
Targetcorrosion
corrosionrate
rateof
of8%;
8%;(c)
(c)Target
Targetcorrosion
corrosionrate
rateofof15%.
15%.

3.2.
3.2. Failure
Failure Modes
Modes of
of Test
TestSpecimens
Specimens
Figure
Figure 66 shows
shows the
the crack
crack patterns
patterns of
of the
the specimens
specimens atat failure,
failure, where
where thethe cracks
cracks induced
induced byby
longitudinal
longitudinal reinforcement corrosion (i.e., corrosion cracks) are represented as red lines. The
reinforcement corrosion (i.e., corrosion cracks) are represented as red lines. The TS-0,
TS-0,
TS-3,
TS-3, TH-0, and TH-3
TH-0, and TH-3specimens
specimenswithwithnonocorrosion
corrosiondamage
damage oror with
with insignificant
insignificant damage
damage showed
showed the
the typical shear failure modes. Meanwhile, the TS-8 specimen (ωcorr = 4.13%) with relatively large
typical shear failure modes. Meanwhile, the TS-8 specimen ( ωcorr = 4.13%) with relatively large
corrosion damage exhibited a shear-bond failure mode as shear cracks were connected with corrosion
corrosion
cracks, anddamage exhibited
the crack a shear-bond
width increased failure
rapidly. mode
In the as shear
TH-8 cracks
specimen (ωwere connected with corrosion
corr = 4.64%), the widths of the
cracks, and
corrosion the crack
cracks tendedwidth increased
to increase withrapidly.
increasing In shear
the TH-8 widths as( ω
crackspecimen the load
corr = 4.64%), theand
increased, widths of
failure
occurred rapidly
the corrosion as anchorage
cracks cracks progressed
tended to increase at the end
with increasing ofcrack
shear the member. The
widths as theTS-15
load (ω corr = 9.76%)
increased, and
failure occurred rapidly as anchorage cracks progressed at the end of the member. The TS-15 ( ωcorr
and TH-15 (ω corr = 8.82%) specimens with severe corrosion damage showed the typical bond failure
modes. The number of flexural cracks in these specimens was smaller than that in other specimens
= 9.76%)
due to theand
decreased
ωcorr performance
TH-15 (bond = 8.82%) specimens
betweenwith severe
tension corrosion damage
reinforcement showed
and concrete. the typical
Furthermore,
bond
as the failure modes. The
load increased, thenumber
splittingofcracks
flexural cracks
caused byincorrosion
these specimens was smaller
became wider, thaninthat
resulting in other
spalling of
specimens due
concrete cover. to the decreased bond performance between tension reinforcement and concrete.
Materials
Materials2019,
2019,12,
12,xxFOR
FORPEER
PEERREVIEW
REVIEW 88ofof1919

Materials 2019, 12, 837 8 of 19

Furthermore,
Furthermore,as asthe
theload
loadincreased,
increased,the
thesplitting
splittingcracks
crackscaused
causedby
bycorrosion
corrosionbecame
becamewider,
wider,resulting
resulting
ininspalling
spallingofofconcrete
concretecover.
cover.

Failure
Failuremode:
mode:shear
shear Failure
Failuremode:
mode:shear
shear
(a)
(a) (b)
(b)

Failure
Failuremode:
mode:shear
shear++bond
bond Failure
Failuremode:
mode:bond
bond
(c)
(c) (d)
(d)

Failure
Failuremode:
mode:shear
shear Failure
Failuremode:
mode:shear
shear
(e)
(e) (f)
(f)

Failure
Failuremode:
mode:shear
shear++bond
bond Failure
Failuremode:
mode:bond
bond
(g)
(g) (h)
(h)
Figure
Figure6.
6.6.Crack
Crackpatterns
Crackpatternsofoftest
patterns specimens
oftest
test after
specimens
specimens failure.
after
after (a)
(a)TS-0
failure.
failure. (a)specimen;
TS-0 (b)
(b)TS-3
TS-0 specimen;
specimen; specimen;
(b)
TS-3 (c)
(c)TS-8
TS-3 specimen;
specimen; TS-8
specimen;
(c) (d)
(d)TS-15
TS-8 specimen;
specimen; specimen;
(d)
TS-15 (e)
(e)TH-0
TS-15 specimen;
specimen; TH-0specimen;
(e) (f)
(f)TH-3
TH-3specimen;
TH-0 specimen;
specimen; (g)
(g)TH-8
TH-8specimen;
(f) TH-3 specimen;
specimen; (g) TH-8 (h)
specimen; (h)TH-15
specimen;
TH-15
specimen.
(h) TH-15 specimen.
specimen.

Figure
Figure77shows
showsshear
shearstrain
straindistributions
distributionsmeasured
measuredusing usingthetherelative
relativedisplacement
displacementofofthe thetarget
target
shown in Figure 3b.
shown in Figure 3b.For For the
Forthe TS-0,
theTS-0, TS-3,
TS-0,TS-3, TH-0,
TS-3,TH-0, and
TH-0,and TH-3
andTH-3 specimens,
TH-3specimens, in
specimens,ininwhichwhich no
whichno tension
notension reinforcement
tensionreinforcement
reinforcement
corrosionwas
corrosion wasintroduced
was introduced
introduced ororininwhich
or inwhich
whichcorrosion
corrosionlevels
corrosion levelswere
levels relatively
were
were low,low,
relatively
relatively the
low,members
the failedfailed
themembers
members in shear
failedinin
as shear
shear as deformation
shear was
deformation concentrated
was in the
concentrated concrete
in the web.
concreteIn addition,
web. In the TS-8
addition,
shear as shear deformation was concentrated in the concrete web. In addition, the TS-8 and TH-8 and
the TH-8
TS-8 specimens
and TH-8
showed
specimens
specimenstheshowed
shear-bond
showed the failure
theshear-bond
shear-bond modes, resulting
failure
failure modes,
modes, from combined
resulting
resulting fromdeformations
from combined due to the shear
combineddeformations
deformations duetoforce
due tothe
the
and
shearthe bond
force andloss.
the In
bondthe cases
loss. In of
the the
casesTS-15
of and
the TH-15
TS-15 and specimens
TH-15 with
specimens very
with
shear force and the bond loss. In the cases of the TS-15 and TH-15 specimens with very high corrosion high
verycorrosion
high rates,
corrosion
the deformations
rates,
rates,the due todue
thedeformations
deformations bond
due totoloss
bond
bondwere
lossfound
loss were to
werefound dominate
found the failure
totodominate
dominate the modesmodes
thefailure
failure of theof
modes specimens.
ofthe
thespecimens.
specimens.

(a)
(a)
Figure 7. Cont.
Materials 2019,12,
Materials2019, 12,837
x FOR PEER REVIEW 99 of
of1919

Failure side
CL <Shear strain distribution>

(b)

Failure side <Shear strain distribution>

CL

(c)

(d)

(e)

(f)

Failure side <Shear strain distribution>

CL

(g)
Figure 7. Cont.
Materials 2019,12,
Materials2019, 12,837
x FOR PEER REVIEW 10 of
of 19
19

Failure side <Shear strain distribution>

CL

(h)
Figure 7.
Figure 7. Shear
Shearstrain
straindistributions at failure
distributions loads.
at failure (a) TS-0
loads. (a) specimen; (b) TS-3(b)specimen;
TS-0 specimen; (c) TS-8
TS-3 specimen;
(c) TS-8 specimen;
specimen; (d) TS-15(d)specimen;
TS-15 specimen;
(e) TH-0(e) TH-0 specimen;
specimen; (f) TH-3 specimen;
(f) TH-3 specimen; (g) TH-8 specimen;
(g) TH-8 specimen; (h) TH-15
(h) TH-15 specimen.
specimen.

3.3.
3.3.Shear
ShearBehaviors
BehaviorsofofTestTestSpecimens
Specimens
Figures
Figures 8 and 9 show shear
8 and 9 show the behaviors
the shear of the TS
behaviors of and
the TH
TS series
and THspecimens, while Table while
series specimens, 3 summarizes
Table 3
the shear test the
summarizes results.
shearIntesttheresults.
TS-0 specimen,
In the TS-0thespecimen,
referencethespecimen of TS
reference series, the
specimen initial
of TS shear
series, the crack
initial
occurred at a occurred
shear crack load of about at a 105
loadkN. Then, a105
of about horizontal
kN. Then, bond crack toward
a horizontal bondthecrack
support was observed
toward the supportat
awas
loadobserved
of 138 kN,atand shearoffailure
a load 138 kN, occurred at a load
and shear of 238.6
failure kN. Inatthe
occurred TS-3 of
a load specimen
238.6 kN.(ωcorr
In =the
1.14%)
TS-3
with a target corrosion rate of 3%, the initial shear crack occurred at a load similar to that of the
specimen ( ωcorr = 1.14%) with a target corrosion rate of 3%, the initial shear crack occurred at a load
reference specimen (P = 116 kN), and then underwent shear failure at a load of 281.4 kN. The TS-3
similar to that of
specimen showed a shearthe reference specimen
capacity ( P =18%
of about 116 kN), andthan
higher thenthat
underwent shearspecimen.
of the TS-0 failure at aThis
load is
of
281.4 kN.
because, at The
a lowTS-3 specimen
corrosion showed
rate of a shear
less than 2%, the capacity
expansionof about 18%(i.e.,
pressure higher than that
corrosion of theofTS-0
pressure) the
specimen. This
reinforcement is because,
caused at a low contributes
by the corrosion corrosion rate of improvement
to the less than 2%,ofthe bondexpansion pressure
performance (i.e.,
between
corrosion pressure)
reinforcement of the [8,31],
and concrete reinforcement
and this caused
phenomenonby thewascorrosion contributes
observed to the improvement
in the experiment conducted by of
bond performance
Lachemi et al. [21]. Inbetween
the TS-8reinforcement
specimen (ωcorrand concrete
= 4.13%) with [8,31], andcorrosion
a target this phenomenon
rate of 8%,was observed
a decrease in
in theperformance
bond experiment conducted by Lachemi
due to tension et al. [21].
reinforcement In the TS-8
corrosion causedspecimen ( ωcorr effect
a detrimental = 4.13%) withmember
on the a target
behavior. An anchorage crack was observed at a load of about 100 kN. The splitting
corrosion rate of 8%, a decrease in bond performance due to tension reinforcement corrosion causedcrack progressed
at
a the same time
detrimental when
effect onthe
theshear crackbehavior.
member occurredAn at aanchorage
load of 148crack
kN, then
was the member
observed at failed
a loadatofaabout
load
of 212.4
100 kN.kN.
TheThe shear capacity
splitting of the TS-8
crack progressed at specimen was 11%
the same time when smaller thancrack
the shear that of the TS-0atspecimen.
occurred a load of
The TS-15 specimen (ω = 9.76%) with a target corrosion rate of 15% showed distinct
148 kN, then the member failed at a load of 212.4 kN. The shear capacity of the TS-8 specimen was
corr reductions in
11% smaller than that of the TS-0 specimen. The TS-15 specimen ( ωcorr = 9.76%) with a target
stiffness and capacity due to corrosion. As shown in Figure 8e, the TS-15 specimen, as compared to
the TS-0 specimen, showed very low stiffness from the beginning of the behavior, and the widths of
corrosion rate of 15% showed distinct reductions in stiffness and capacity due to corrosion. As shown
the corrosion cracks became significantly larger with the increasing loads. As a result, bond failure
in Figure 8e, the TS-15 specimen, as compared to the TS-0 specimen, showed very low stiffness from
occurred at a load of 161.1 kN, a reduction of 30% as compared to the failure load of the TS-0 specimen.
the beginning of the behavior, and the widths of the corrosion cracks became significantly larger with
This is because the corroded reinforcement could not exert the tensile stress required to resist the
the increasing loads. As a result, bond failure occurred at a load of 161.1 kN, a reduction of 30% as
external moment due to bond loss between the reinforcement and concrete.
compared to the failure load of the TS-0 specimen. This is because the corroded reinforcement could
not exert the tensile stress required toSummary
Table 3. resist theof external
shear test moment
results. due to bond loss between the
reinforcement and concrete.
Specimen ωcorr (%) Pn (kN) Vn (kN) ∆mid (mm) Failure Mode Strength Ratio *
TS-0 0 238.6 119.3
Table 3. Summary 5.54 test results. Shear
of shear 1.00
TS-3 1.14 281.4 140.7 6.84 Shear 1.18
SpecimenTS-8 ωcorr (%)
4.13 Pn (kN)
212.4 Vn (kN)
106.2 ∆mid (mm)
5.21 Failure
Shear + Mode
bond Strength
0.89 Ratio*
TS-0TS-15 0 9.76 168.1
238.6 119.3 84.1 6.76
5.54 Bond
Shear 0.701.00
TH-0 0 198.0 99.0 4.82 Shear 1.00
TS-3TH-3 1.141.64 281.4
235.2 140.7117.6 6.84
4.74 Shear
Shear 1.191.18
TS-8TH-8 4.134.64 212.4
228.5 106.2114.3 5.21
6.94 Shear
Shear ++ bond
bond 1.150.89
TS-15TH-15 9.768.82 213.6
168.1 84.1106.8 8.99
6.76 Bond
Bond 1.080.70
TH-0 * Shear0strength ratio of the specimens
198.0 99.0 to the reference
4.82specimens (TS-0Shear
and TH-0 specimens). 1.00
TH-3 1.64 235.2 117.6 4.74 Shear 1.19
TH-8 4.64 228.5 114.3 6.94 Shear + bond 1.15
TH-15 8.82 213.6 106.8 8.99 Bond 1.08
* Shear strength ratio of the specimens to the reference specimens (TS-0 and TH-0 specimens).
Materials2019,
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Materials 2019, 12, x FOR PEER REVIEW 11 of 19

300
300 ④
④
300
④
④
300
250
250 250
250
200
(kN)

200

(kN)
200
Load(kN)

③ 200 ③

Load(kN)
150 ③ ③
150 ②
②
150
②
150
②
Load

①: Flexural cracking (P = 76 kN)

Load
100 ①
① ①: Flexural cracking (P = 76 kN)
②: First shear cracking (P = 105 kN) 100
①: Flexural cracking (P = 60 kN)
①: Flexural cracking (P = 60 kN)
100
②: First shear cracking (P = 105 kN) 100 ①
①
②: Inclined nshear crack (P = 116 kN)
②: Inclined nshear crack (P = 116 kN)
50 ③: Observe splitting crack (P = 138 kN) ③: Second shear cracking (P = 148 kN)
50 ③: Observe splitting crack (P = 138 kN) 50
③: Second shear cracking (P = 148 kN)
④: Failure (P = 238.6 kN) 50
④: Failure (P = 281.4 kN)
0 ④: Failure (P = 238.6 kN) ④: Failure (P = 281.4 kN)
0 0 0
2 4 6 8 10 0 0
0 2 4 6 8 10 2 4 6 8 10
0 2 4 6 8 10
Displacement (mm) Displacement (mm)
Displacement (mm) Displacement (mm)

(a)
(a) (b)
(b)
300 300
300 300 ①: Flexural cracking (P = 70 kN)
①: Flexural cracking (P = 70 kN)
250
④ 250 ②: Develop splitting crack (P = 145 kN)
250
④ 250 ②: Develop splitting crack (P = 145 kN)
③ ③: Failure (P = 168.1 kN)
③ 200 ③: Failure (P = 168.1 kN)
③

(kN)
200
(kN)

200
③

Load(kN)
200
Load(kN)

150 150 ②
②
150
② 150

Load
②
Load

①: Flexural cracking (P = 69 kN)

100
100 ① ①: Flexural cracking (P = 69 kN)
②: Anchorage cracking (P = 100 kN)
100
100 ①
①
50
① ②: Anchorage cracking (P = 100 kN)
③: Develop splitting and shear cracks (P = 148 kN) 50
50 ③: Develop splitting and shear cracks (P = 148 kN) 50
④: Failure (P = 212.4 kN)
0 ④: Failure (P = 212.4 kN) 0
0 0 2 4 6 8 10 0 0
0 2 4 6 8 10
2 4 6 8 10 12 14
0 2 4 6 8 10 12 14
Displacement (mm) Displacement (mm)
Displacement (mm) Displacement (mm)

(c)
(c) (d)
(d)
300
300 TS-0
TS-0
250 TS-3
250 TS-3
TS-8
200 TS-8
(kN)

200 TS-15
Load(kN)

TS-15
150
150
Load

100
100
50
50
0
0 0 2 4 6 8 10 12 14
0 2 4 6 8 10 12 14
Displacement (mm)
Displacement (mm)

(e)
(e)
Figure Load-displacementresponses
Figure8.8.Load-displacement responsesofofTS
TSseries
seriesspecimens.
specimens.(a)
(a)TS-0
TS-0specimen;
specimen;(b)
(b)TS-3
TS-3specimen;
specimen;
Figure 8. Load-displacement responses of TS series specimens. (a) TS-0 specimen; (b) TS-3 specimen;
(c) TS-8 specimen; (d) TS-15 specimen; (e) Comparison of TS series test results.
(c) TS-8 specimen; (d) TS-15 specimen; (e) Comparison of TS series test results.
(c) TS-8 specimen; (d) TS-15 specimen; (e) Comparison of TS series test results.

250
250 250
④
④
④
④
250
200
200 200
200 ③
③
③
(kN)

③ ②
(kN)
Load(kN)

150
②
Load(kN)

150
②
150
150
②
Load

100
①: Flexural cracking (P = 22 kN)
Load

100
100
①: Flexural cracking (P = 22 kN) ①: Flexural cracking (P = 55 kN)
②: Web shear cracking (P = 105 kN)
100
①
①
①: Flexural cracking (P = 55 kN)
②: Inclined shear crack (P = 146 kN)
50 ① ②: Web shear cracking (P = 105 kN) ②: Inclined shear crack (P = 146 kN)
③: Observe splitting crack (P = 138 kN)
50 ① ③: Observe splitting crack (P = 138 kN)
50
50 ③: Second shear cracking (P = 165 kN)
③: Second shear cracking (P = 165 kN)
④: Failure (P = 198.0 kN) ④: Failure (P = 235.2 kN)
0 ④: Failure (P = 198.0 kN) ④: Failure (P = 235.2 kN)
0 0 0
1 2 3 4 5 6 7 0 0
0 1 2 3 4 5 6 7 2 4 6 8 10
0 2 4 6 8 10
Displacement
Displacement (mm) Displacement
(mm) Displacement (mm)
(mm)
(a)
(a) (b)
(b)
Figure 9. Cont.
Materials 2019, 12, 837 12 of 19
Materials 2019, 12, x FOR PEER REVIEW 12 of 19

250 ③ 250
③
200 200
②

Load (kN)
Load (kN)

150 150
②
100 100
① ①: Flexural cracking (P = 65 kN) ①: Flexural cracking (P = 28 kN)
②: Inclined shear cracking (P = 120 kN) 50 ① ②: Anchorage cracking (P = 180 kN)
50
③: Develop splitting and anchorage cracks ③: Develop splitting crack and failure (P = 213.6 kN)
and failure (P = 228.5 kN) 0
0
0 2 4 6 8 10 12 14 16
0 2 4 6 8 10 12

Displacement (mm) Displacement (mm)

(c) (d)
250

200
Load (kN)

150

100 TH-0
TH-3
50 TH-8
TH-15
0
0 2 4 6 8 10 12 14

Displacement (mm)
(e)
Figure
Figure9.9.Load-displacement
Load-displacement responses
responses of
of TH
TH series
series specimens.
specimens. (a)
(a)TH-0
TH-0specimen;
specimen; (b)
(b) TH-3
TH-3 specimen;
specimen;
(c)
(c) TH-8
TH-8 specimen;
specimen; (d)
(d) TH-15
TH-15 specimen;
specimen; (e)
(e) Comparison
Comparison of TH series test results.

Figure 9a
Figure 9a shows
shows thatthat inin the
the TH-0
TH-0 specimen,
specimen, the the reference
reference specimen
specimen of of TH
TH series,
series, aa web-shear
web-shear
crack was observed at a load of about 105 kN, a horizontal crack toward
crack was observed at a load of about 105 kN, a horizontal crack toward the support took place the support took place at at aa
load of
load of 138
138 kN,
kN, and
and then
then shear
shear failure
failure occurred
occurred at at aa load
load of
of 198
198 kN.
kN. As As shown
shown in in Figure
Figure 9e,9e, the
the TH-3
TH-3
specimen ( ωcorr
specimen (ω = 1.64%) showed greater stiffness than the TH-0 specimen
corr = 1.64%) showed greater stiffness than the TH-0 specimen from the beginning of the from the beginning of the
behavior, and also underwent shear failure at a load of 235.2 kN, which is about 19% higher than the
behavior, and also underwent shear failure at a load of 235.2 kN, which is about 19% higher than the
load at which the TH-0 specimen underwent shear failure. The reason for why the TH-3 specimen
load at which the TH-0 specimen underwent shear failure. The reason for why the TH-3 specimen
showed greater stiffness and capacity than the TH-0 specimen is that, as mentioned previously, the
showed greater stiffness and capacity than the TH-0 specimen is that, as mentioned previously, the
bond performance between the reinforcement and concrete improves at a low corrosion rate. The initial
bond performance between the reinforcement and concrete improves at a low corrosion rate. The
stiffness of the TH-8 specimen (ωcorr = 4.64%), which has a relatively high corrosion rate, was smaller
initial stiffness
than that of theof TH-0
the TH-8 specimen
specimen. The( ωreason
corr = 4.64%),
for thiswhich
is that has a relatively
the widths ofhigh corrosion
corrosion cracksrate,inwas
the
smaller than thatwere
TH-8 specimen of themuchTH-0 specimen.
larger The reason
than those generated for this is that
in the TS-8the widths as
specimen, of shown
corrosion cracks 5b.
in Figure in
the
ThisTH-8 specimen
suggests were
that the much larger
reduction of bondthanperformance
those generated in the
in the TH-8TS-8 specimen,
specimen as shown
is greater in Figure
than that in
5b. This suggests that the reduction of bond performance in the TH-8
the TS-8 specimen. It is noted that the initial stiffness of the TS-8 specimen was almost the same specimen is greater than that
as
in theofTS-8
that the specimen.
TS-0 specimen,It is noted that the
as shown initial stiffness
in Figure of the TS-8
8e. However, unlike specimen
in the TS-8wasspecimen
almost thewithout
same asa
that of the
proper TS-0 specimen,
anchorage (ωcorr = as shown
4.13%), theinfailure
Figureload8e. However,
of the TH-8 unlike in thewas
specimen TS-8228.5
specimen without aa
kN, indicating
proper anchorage ( ω
15% improvement ascorr
compared
= 4.13%), tothe
thefailure
TH-0 specimen
load of thewith TH-8 nospecimen
corrosionwas damage.
228.5 kN, This is because
indicating a
the tension reinforcement that has been properly anchored at the
15% improvement as compared to the TH-0 specimen with no corrosion damage. This is because the end could exert the tensile stress
requiredreinforcement
tension to resist the external
that has moment, even if the
been properly bond performance
anchored at the end between
could exertthe reinforcement
the tensile stress and
concrete decreased rapidly as the corrosion progressed. The initial behavior
required to resist the external moment, even if the bond performance between the reinforcement and of the TH-15 specimen
(ωcorr = 8.82%),
concrete decreased which has as
rapidly a very high corrosion
the corrosion rate ofThe
progressed. tension
initialreinforcement,
behavior of the was similar
TH-15 to that
specimen
( ωcorr = 8.82%), which has
of the TH-8 specimen (ωcorr = 4.64%). However, in the TH-15 specimen, inclined shear cracks were
a very high corrosion rate of tension reinforcement, was similar to that of
not observed during the loading process, as only a few flexural cracks took place at the tops of the
the TH-8 specimen
corrosion ωcorr =in4.64%).
cracks, as(shown Figure However,
6h. These crackin thepatterns
TH-15 specimen,
occur when inclined shear
the crack cracks
control were not
capability is
observed during the loading process, as only a few flexural cracks took place at the tops of the
corrosion cracks, as shown in Figure 6h. These crack patterns occur when the crack control capability
Materials 2019, 12, 837
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of 19

is insufficient, as the bond performance between the reinforcement and concrete is reduced by
insufficient,Nevertheless,
corrosion. as the bond performance
the capacity between the reinforcement
of the TH-15 specimen wasand concrete
213.6 is reduced
kN, which is aboutby8%corrosion.
higher
than that of the TH-0 specimen. This is because, as mentioned previously, even if thethat
Nevertheless, the capacity of the TH-15 specimen was 213.6 kN, which is about 8% higher than of
bond
the TH-0 specimen.
performance This is because,
of the reinforcement as mentioned
decreased due topreviously, even
corrosion, the if the bondreinforcement
longitudinal performance of the
could
reinforcement decreased due to corrosion, the longitudinal reinforcement
exert tensile stress due to the development of bearing stress at the hooks of the reinforcement could exert tensile stress
due to theatdevelopment
anchored the ends of the of member.
bearing stress at theunlike
Therefore, hooksthe of TS-15
the reinforcement
specimen that anchored
underwent at the ends of
premature
the member.
bond failure, Therefore,
the TH-15 unlike
specimen the exhibited
TS-15 specimen thatload-carrying
sufficient underwent premature
capacity. bond failure, the TH-15
specimen exhibited sufficient load-carrying capacity.
As shown in Figure 10, the shear capacities of the TS-3 and TH-3 specimens with low
As shown in
reinforcement Figure 10,
corrosion the shear
levels (i.e.,capacities
lower than of the TS-3 2%)
about and TH-3
tendedspecimens with by
to increase lowabout
reinforcement
20% as
corrosion levels (i.e., lower than about 2%) tended to increase by about 20%
compared to those of the reference specimens. However, in the cases of the TS-8 and TS-15 specimens as compared to those of
the reference specimens. However, in the cases of the TS-8 and TS-15 specimens
with a high corrosion rate of more than 4%, in which the tension reinforcement had not been properly with a high corrosion
rate of more
anchored thanends
at the 4%, of in which the tension
the members, reinforcement
the capacities hadspecimens
of the not been decreased
properly anchored
sharply as at the
the
ends of the members, the capacities of the specimens decreased sharply
corrosion rate of the longitudinal reinforcement increased. By contrast, in the TH-8 and TH-15 as the corrosion rate of the
longitudinalinreinforcement
specimens which the tension increased. By contrast,
reinforcement in been
had the TH-8 and TH-15
properly specimens
anchored at the in which
ends the
of the
tension reinforcement
members in the form had been properly
of hooks, an increaseanchored at the ends
in corrosion rate of
didthe
notmembers
lead to in the formreduction
a capacity of hooks, an of
increase in corrosion rate did not lead to a capacity reduction of
the member, and instead the capacity tended to further increase as compared to the the member, and instead thereference
capacity
tended to further increase as compared to the reference specimen.
specimen.

160
TS series TH series
140
Shear capacity (kN)

120

100

80

60

40

20

0
0 0%0 1.13%1.6 4.18%4.6 9.815%
8.8
Actual corrosion rate (%)
Figure 10. Effects of corrosion rates on shear capacities of test specimens.
Figure 10. Effects of corrosion rates on shear capacities of test specimens.
3.4. Measured Strains of Stirrups
3.4. Measured Strains of Stirrups
Figure 11 shows the strains measured from the gauges attached to the transverse reinforcement in
Figure 11 shows
test specimens. the be
It should strains
noted measured
that epoxy from the gauges
coated attached
transverse to the transverse
reinforcement was used reinforcement
in this study
in test specimens. It should be noted that epoxy coated transverse reinforcement
to prevent corrosion of stirrups. In the TS-0, TS-3, TH-0, and TH-3 specimens, which showed was used typical
in this
study to prevent
shear failure corrosion
modes, of stirrups.
the strains of shearInreinforcement
the TS-0, TS-3, TH-0, and
increased TH-3 specimens,
sufficiently from the which showed
shear cracking
typical shearsuggests
loads. This failure modes,
that thethe strains
shear of shear reinforcement
reinforcement contributed to increased
the shearsufficiently
resistance from the shear
mechanism of
cracking
the member. loads.
ByThis suggests
contrast, almost thatnothe shear
strains of reinforcement contributed
shear reinforcement or verytosmall
the shear
strainsresistance
of shear
mechanism
reinforcement of the
weremember. By contrast,
measured in the TS-15almostandnoTH-15
strainsspecimens
of shear reinforcement
with very high or corrosion
very smallrates
strains
of
of shear reinforcement were measured in the TS-15 and TH-15 specimens with very
tension reinforcement. This is because the failure of these specimens was dominated by the bond loss high corrosion
rates
betweenof tension reinforcement.
the longitudinal This is because
reinforcement the failure
and concrete ratherofthan
thesethe
specimens
shear. was dominated by the
bond loss between the longitudinal reinforcement and concrete rather than the shear.
 Materials 2019, 12, 837 14 of 19
Materials 2019, 12, x FOR PEER REVIEW 14 of 19

300

250

Load (kN)
200

150

100
TS-0 TS-3
50 TS-8 TS-15
0
-500 0 500 1000 1500 2000 2500 3000
Strain (με)

(a)
250

200
Load (kN)

150

100
TH-0 TH-3
50
TH-8 TH-15
0
-2000 0 2000 4000 6000 8000
Strain (με)

(b)
Figure 11.11.
Figure Measured strains
Measured of of
strains stirrups. (a)(a)
stirrups. TSTS
series specimens;
series (b)(b)
specimens; THTH
series specimens.
series specimens.

4. 4. Discussion
Discussion
The
The TH TH series
series specimens
specimens exhibited
exhibited a further
a further increase
increase in inthethe shear
shear capacity
capacity of of
thethe member
member asas
compared
compared to to
thethe non-corroded
non-corroded specimen,
specimen, despite
despite thethe corrosion
corrosion of of longitudinal
longitudinal reinforcement.
reinforcement. Azam
Azam
and Soudki [17,18] reported that, when tension reinforcing bars were properly
and Soudki [17,18] reported that, when tension reinforcing bars were properly anchored at the ends anchored at the ends
of of
thethe member,
member, itsits shear
shear capacity
capacity increased
increased byby
upuptoto two
two times
times asas thethe longitudinal
longitudinal reinforcing
reinforcing bars
bars
corroded. They also indicated that this was because the load transfer
corroded. They also indicated that this was because the load transfer mechanism of the member was mechanism of the member
was changed
changed from beam from action
beam action
to archtoaction.
arch action. Therefore,
Therefore, in this in this study,
study, the capacity
the shear shear capacity
of the of testthe
test specimens
specimens was evaluated
was evaluated usingusing a strut-and-tie
a strut-and-tie model model
(STM) (STM) in consideration
in consideration of of
thethe arch-action
arch-action
mechanism and equations for estimating shear capacity presented in
mechanism and equations for estimating shear capacity presented in the ACI 318-14 building the ACI 318-14 building code
code[25].
[25]. The ACI 318-14 code provides the shear capacity equations for slender RC members, as follows:
The ACI 318-14 code provides the shear  capacity equationsfor slender RC members, as follows:
p Vu ds
Vc = 0.16 f c 0 + 17ρw bw d s (2a)
 V dMu
Vc =  0.16 f c′ + 17 ρ w u s
 bw d s (2a)
 Av f vy dM
s u 
Vs = (2b)
sv
Av f vy d s
VsV=n = Vc + Vs (2b)(2c)
sv
where Vc and Vs are the shear contribution of Vn concrete
= Vc + Vand stirrups, respectively; f c 0 is the compressive
(2c)
s
strength of concrete (MPa); Vu and Mu are the external shear force (N) and moment (N·mm) at
where Vc and Vs are the shear contribution of concrete and stirrups, respectively; f c ′ is the
critical section; ds is the effective depth of reinforcement (mm); bw is the web width (mm); Av is
compressive strength
the sectional area ofof concrete
stirrup (mm (MPa); V and M are the external shear force (N) and moment
2 ); f is
vy u the yield ustrength of transverse reinforcement (MPa); sv is
(N·mm) at critical section; ds is the effective depth of reinforcement (mm); bw is the web width
(mm); Av is the sectional area of stirrup (mm2); fvy is the yield strength of transverse
Materials 2019, 12, x FOR PEER REVIEW 15 of 19

reinforcement (MPa); sv is the spacing between stirrups (mm), and ρ w is the reinforcement ratio,
which can be calculated by As (1 − ωcorr ) / ( bw d s ) considering the loss of cross-sectional area of
Materials 2019, 12, 837 15 of 19
longitudinal reinforcement.
In this study, two failure modes (i.e., concrete strut failure or tension tie yield) were considered
for
thethe analysis
spacing using the
between STM, (mm),
stirrups as follows:
and ρw is the reinforcement ratio, which can be calculated by
As (1 − ωcorr )/(bw ds ) considering the loss of cross-sectional area of longitudinal reinforcement.
In this study, two failure modes (i.e., = 0.85βstrut
Fnsconcrete ′ ws
s fc bwfailure
(3a)
or tension tie yield) were considered
for the analysis using the STM, as follows:
Fnt = Ats f y (3b)
Fns = 0.85β s f c 0 bw ws (3a)

Vn = min (FFntns =
sinAθts, fF
y nt
tan θ ) (3c)
(3b)

where Fns and Fnt are the strengthVof

n = min( Fnsstrut
concrete tan θ ) ties, respectively; β s is the strut
Fnt tension
sin θ,and (3c)
effectiveness
where Fns andcoefficient, taken
Fnt are the to be 1.0;
strength ws is thestrut
of concrete width
andoftension
compressive strut (mm), which
ties, respectively;β can be
s is the strut
estimated
effectiveness lb sin θ + wt cos
by coefficient, θ ; to
taken lb is
be the
1.0;width of bearing
ws is the width ofplate w
(mm); strut
compressive t is the height
(mm), of C-C-T
which can be
estimated
nodal by lb sin
zone (mm), andθ +θ wist cos lb is the angle
theθ;inclination widthbetween
of bearing
compressive strutwand
plate (mm); t is tension
the height of C-C-T
ties (rad). In
nodal zone
addition, Ats (mm),
is the and θ is the
sectional areainclination angle
of corroded between
tension compressive
reinforcement (mmstrut
2 and can
), which tension ties (rad).
be calculated
2
As (1 − ωcorr A
asIn addition, ) .ts is the sectional area of corroded tension reinforcement (mm ), which can be calculated
as As (1 − ωcorr ).
Figure 12 shows a comparison of the test and analysis results. The shear capacity equations
Figure 12 shows a comparison of the test and analysis results. The shear capacity equations
presented in the current ACI 318-14 building code provided a relatively close evaluation on the shear
presented in the current ACI 318-14 building code provided a relatively close evaluation on the shear
capacities of RC specimens with a corrosion rate of less than 2%, but significantly overestimated the
capacities of RC specimens with a corrosion rate of less than 2%, but significantly overestimated the
shear capacities of the TS-8 and TS-15 specimens with a corrosion rate of more than 4%, and the
shear capacities of the TS-8 and TS-15 specimens with a corrosion rate of more than 4%, and the tension
tension reinforcement that had not been properly anchored at the ends of the member. This suggests
reinforcement that had not been properly anchored at the ends of the member. This suggests that
that the shear capacity is affected more by the reduction of bond performance than by the decrease
the shear capacity is affected more by the reduction of bond performance than by the decrease in the
in the sectional area of tension reinforcement due to corrosion. By contrast, in the TH-8 and TH-15
sectional area of tension reinforcement due to corrosion. By contrast, in the TH-8 and TH-15 specimens
specimens in which the tension reinforcement had been properly anchored at the ends of the
in which the tension reinforcement had been properly anchored at the ends of the members, there
members, there was no substantial difference between the analysis and test results, as the corrosion
was no substantial difference between the analysis and test results, as the corrosion of longitudinal
of longitudinal reinforcement did not significantly affect the capacities of the members due to arch
reinforcement did not significantly affect the capacities of the members due to arch action.
action.
160 TS-3
140
Shear capacity (kN)

120
TS-0
100 TS-8
80
TS-15
60 CL
Test results
40 Anchored without
ACI 318
hooks
20 STM
0
0 2 4 6 8 10
Corrosion rate (mass loss, %)

(a)
Figure 12. Cont.
Materials2019,
Materials 12,x837
2019,12, FOR PEER REVIEW 1616ofof19
19

160
140

Shear capacity (kN)

120
100 TH-3 TH-8
TH-0 TH-15
80
CL
60 Test results
40 Anchored ACI 318
20 with hooks STM
0
0 2 4 6 8 10
Corrosion rate (mass loss, %)

(b)
Figure
Figure12.
12.Comparisons
Comparisonsof
oftest
testand
andanalysis
analysisresults.
results. (a)
(a)TS
TSseries
seriesspecimens;
specimens;(b)
(b)TH
THseries
seriesspecimens.
specimens.

As shown
As shown in in Figure
Figure 12a,
12a, the
the STM
STM provided
provided an an excessive
excessive overestimation
overestimation on on the
the shear
shear capacities
capacities
of the
of theTS-8
TS-8andandTS-15
TS-15specimens.
specimens.This This is because
is because thethe tension
tension tiesties of the
of the TS series
TS series specimens
specimens had had
not
not been
been properly
properly anchored,
anchored, whilewhile a precondition
a precondition of theofapplication
the application of theofSTM
the STMis thatis that the tension
the tension ties
ties should
should be properly
be properly anchored
anchored at theat the
ends ends
of ofthethe members.
members. Unlike
Unlike in in
thethecases
casesofofthe theTS TS series
series
specimens, as
specimens, as shown
shown in in Figure
Figure 12b,
12b, thethe STM
STM provided
provided aa relatively
relatively approximate
approximate prediction
prediction on on the
the
tendency of
tendency of shear
shear capacity
capacity changes
changes in in the
the TH-3,
TH-3, TH-8,
TH-8, and
and TH-15
TH-15 specimens,
specimens, in in which
which the the tension
tension
reinforcementhad
reinforcement hadbeenbeen properly
properly anchored
anchoredat at the
the ends
ends ofof the
the members.
members. However,
However, even even though
though the the
arch-action was
arch-action was reflected
reflected in in the
the shear
shear transfer
transfer mechanism
mechanism through
through the the application
application of of the
the STM,
STM, the the
test and
test and analysis
analysis results
results differed
differed because
because the the STM
STM cannot
cannot appropriately
appropriatelyreflect reflect the
the changes
changes of of bond
bond
performance due
performance due totothethe corrosion
corrosion of tension
of tension reinforcement.
reinforcement.Therefore, furtherfurther
Therefore, research is still required
research is still
to clearlyto
required understand the shear capacity
clearly understand the shear ofcapacity
corrodedofRC membersRC
corroded with proper anchorage
members with proper details, based
anchorage
on which a more proper method for considering the change in the
details, based on which a more proper method for considering the change in the bond performance bond performance of the tension
reinforcement
of due to corrosion
the tension reinforcement duecan be developed.
to corrosion can be developed.
Meanwhile,there
Meanwhile, thereare aremany
manyretrofitting
retrofittingmaterials
materialsusedusedfor forstrengthening
strengtheningcorroded
corrodedRC RCmembers,
members,
such as the
such the fabric
fabricreinforced
reinforcedcementitious
cementitious matrix
matrix(FRCM)
(FRCM)andandthe textile reinforced
the textile mortarmortar
reinforced (TRM)(TRM) [32,33].
If the steel
[32,33]. If thewire
steelmesh
wireismeshapplied to the FRCM
is applied to the FRCMor TRM, the corrosion
or TRM, wouldwould
the corrosion occur occur
with the withsame
the
mechanism as in the case of reinforcing bars. However, since the
same mechanism as in the case of reinforcing bars. However, since the bond mechanism betweenbond mechanism between steel mesh
and concrete
steel mesh and is concrete
different is from that between
different from that reinforcing
betweenbar and concrete,
reinforcing the concrete,
bar and behavior the of the structural
behavior of
members
the withmembers
structural FRCM orwith TRM FRCMwhose orsteel
TRMmesh whose is steel
corroded
meshisisexpected
corrodedtoisbe different
expected tofrom the test
be different
results
from thereported in this
test results study. in
reported Therefore,
this study. additional
Therefore, experimental
additional research
experimentalis required
research to identify
is required the
effects
to of corrosion
identify the effects onofthe RC members
corrosion on thereinforced
RC members withreinforced
FRCM or with TRM.FRCM or TRM.

5. Conclusions
5. Conclusions
In this
In this study,
study, shear
shear tests
tests were
were carried
carried out
out to
to evaluate
evaluate the
the effects
effects of
of corrosion
corrosion occurring
occurring in
in
longitudinal tension
longitudinal tensionreinforcement
reinforcementon the
on shear
the capacity of RC members
shear capacity of RC with transverse
members withreinforcement.
transverse
The shear tests were performed after the introduction of corrosion into the
reinforcement. The shear tests were performed after the introduction of corrosion longitudinal reinforcement
into the
with the usereinforcement
longitudinal of an accelerated
withcorrosion
the use oftechnique, and the
an accelerated crack patterns,
corrosion technique,failure modes,
and the crackand shear
patterns,
behaviors of the test specimens were measured and analyzed in detail. On this basis,
failure modes, and shear behaviors of the test specimens were measured and analyzed in detail. On the following
conclusions
this basis, thecan be drawn:
following conclusions can be drawn:
1.
1. Theactual
The actualcorrosion
corrosionrate
rateintroduced
introducedinto
intothe
thetension
tensionreinforcement
reinforcementof of the
the specimens
specimens differed
differed
fromthe
from thecorrosion
corrosionrate
ratecalculated
calculatedusing
usingFaraday’s
Faraday’slaw.
law. This
Thisisis because
because the
the corrosion
corrosion products
products
causedby
caused bythe
theprogress
progressofofthe
thereinforcement
reinforcementcorrosion
corrosioninterfere
interfere with
with the
the supplies
supplies of
of oxygen
oxygen (O
(O22))
andwater
and water(H(H2O)
2 O)necessary
necessarytotoform
formthe
thecorrosion
corrosioncell,
cell,and
andthe
themagnitude
magnitudeof ofthe
thecurrent
currentdensity
density
( i corr) used in the accelerated corrosion test is considerably large. Therefore, to obtain the target
(i
corr
) used in the accelerated corrosion test is considerably large. Therefore, to obtain the target
Materials 2019, 12, 837 17 of 19

corrosion rate in the test, using a small current density ranging from 150 µA/cm2 to 400 µA/cm2
is desirable.
2. In the TS series specimens in which the tension reinforcement has not been properly anchored at
the ends of the members, the shear capacity of the TS-3 specimen (ωcorr = 1.14%) with a small
corrosion rate increased by 18% as compared to that of the TS-0 specimen. This is due to the bond
performance of reinforcement that improves at a low corrosion rate of less than 2%. However,
the TS-8 (ωcorr = 4.13%) and TS-15 (ωcorr = 9.76%) specimens with high corrosion rates showed
11% and 30% reduced shear capacities, respectively, as compared to the reference specimen.
This is attributed to the detrimental effect of the bond loss caused by the corrosion of longitudinal
reinforcement on the shear capacities of the members.
3. In the TH series specimens in which the tension reinforcement had been properly anchored at
the ends of the members, the shear capacities of the corroded specimens with low corrosion
rates as well as those with high corrosion rates were higher than that of the reference specimen.
In particular, even the TH-15 specimen (ωcorr = 8.82%), which had the highest corrosion rate,
showed an increased capacity of about 8% as compared to the TH-0 specimen. This is because,
despite a reduction in the bond performance between corroded reinforcement and concrete, the
load transfer mechanism changes from beam action to arch action as the reinforcement has been
properly anchored at the ends of the member.
4. The ACI 318-14 code equations overestimated the shear capacities of the corroded specimens
and did not provide good predictions over the shear capacity changes of the test specimens
in accordance with the corrosion rates. This suggests that the influence of a reduction in bond
performance on the shear capacity is more significant than that of a decrease in the sectional area
of tension reinforcement due to corrosion.
5. The STM, which reflects the arch-action mechanism, overestimated the shear capacities of the
corroded specimens because it failed to reflect the reduction of bond performance between
corroded reinforcement and concrete. Therefore, further research is still required to clearly
understand the shear capacity of corroded RC members with proper anchorage details, based on
which a more proper method to reflect the bond performance of the tension reinforcement due to
corrosion can be developed.
6. The research findings of this study indicate that the anchorage details are very important to keep
the shear capacity of RC members exposed to deterioration environment.

Author Contributions: Writing—original draft preparation, S.-J.H.; investigation, H.-E.J. and I.H.; validation,
S.-H.C. and S.-Y.S.; writing—review and editing, and supervision, K.S.K.
Funding: This research was supported by Basic Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of Education (No. 2018R1A4A1025953).
Conflicts of Interest: The authors declare no conflict of interest.

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