奥村組技術研究年報 No.50

2024 年 9 月

Flexural Strengthening of Corrosion-damaged RC Bridge Piers Using
Ultra-High-Performance Concrete Layers: An Experimental Study
Biswas Rajib Kumar ＊Takashi Misawa ＊ ＊Takahiro Saito ＊Abstract
We developed a method for strengthening RC bridge piers affected by corrosion damage. We examined five
single-shaft RC bridge piers of the same dimensions and rebar configuration under reversed cyclic loading, inwhich we applied axial stress of 1 MPa to the specimens. Of the five specimens, two specimens underwent an
average of 10% rebar corrosion (Group 1); another two specimens underwent an average of 15% rebar
corrosion (Group 2); and one specimen served as the control. We retrofitted one specimen from each groupwith ultra-high-performance concrete (UHPC) layers measuring 50 mm in thickness. The results showed that
corroded specimens strengthened with UHPC layers exhibit superior structural performance: for example, themaximum load carrying capacity (MLC) of the 15% corroded specimen increased by 24% compared to thesound specimen. Our results show that the proposed approach is highly effective in strengthening corrosiondamaged RC bridge piers.
Keywords: UHPC, strengthening, cyclic loading, rebar corrosion

1.

Introductionthat would restore structural performance without affecting theoriginal geometry. We used UHPC, an advanced strengthening

Bridges are essential components of the social infrastructurematerial, to enhance the structural performance of the corrodedand significantly affect the national economy. Bridges locatedRC bridge piers. We examined five single-shaft RC bridge piers,

in marine environments are often exposed to corrosion damage.

including sound, corroded, and retrofitted specimens, under

Given the cost of demolition and reconstruction and associatedreversed cyclic loading. Important performance indices for

traffic congestion, replacing an entire damaged bridge may notevaluating the performance of the strengthening scheme

be feasible. Strengthening damaged bridges is a possible

included MLC, ductility, stiffness degradation, energy

alternative; developing a reliable method for strengthening

absorption, and curvature. The results obtained from this study

damaged bridges would represent a major breakthrough.

should prove useful in formulating strategies for maintaining

UHPC is a new construction material that offers structural

corrosion-damaged RC bridge piers.

properties superior to conventional concrete. UHPC offers

2.

modulus of elasticity, compressive strength, and tensile strength

Experimental study1) makingexceding 44 GPa, 155 MPa, and 19 MPa, respectively,

it an ideal strengthening material for damaged reinforced

2.1 Specimens

concrete structures.

Our investigation included five single-shaft RC bridge piers,

2) examined the strengthening effects of UHPC

Yuan et al.

fabricatedjackets on the cyclic response of RC bridge piers. The results

configurations. The specimens were cast with a height of 1,650

showed that a UHPC jacket significantly improves strength andmm and a square cross-section of 400 mm, along with a footing

stiffness. Dadvar et al.3) examined a strengthening techniquewith dimensions measuring 1,500 mm x 1,500 mm x 850 mm.

involving UHPC jacketing for circular RC columns. The results

Each specimen was reinforced with 16 mm deformed

showed that UHPC jackets significantly increase load-carrying

reinforcing bars. The reinforcement ratio for the longitudinal

and energy absorption capacity.

rebars was 2%. We used 13 mm deformed reinforcing bars as

Little is currently known about strengthening corrosion-

stirrups. The specimens were designed in accordance with thedamaged RC bridge piers using UHPC layers. To address thisdesign code of the Japan Society of Civil Engineers (JSCE,

research gap, we sought, in this study, to develop a

2007 ).4) The reinforcement details can be seen in Figure 1(a).

strengthening scheme for corrosion-damaged RC bridge piers

The RC bridge pier specimens were subjected to combined

 ＊技術本部技術研究所土木研究グループ＊＊

技術本部技術研究所- 35 -

to

the

same

dimensions

andreinforcing

奥村組技術研究年報 No.50

2024 年 9 月

Unit in mm

Figure 1. (a) Specimen details (b) Corrosion setup (c) Location of UHPC layer (d) Photo of experimental setup
axial and reverse cyclic loading. During the reversed cyclic

Corrosion process2) was applied to eachloading, an axial force of 160 kN (1 N/mm

After the fabrication and curing of the test specimens, weof the five specimens. Of the five specimens, Case 1 was usedperformed accelerated corrosion testing. The targeted area foras the control specimen; Cases 2 and 3 were subjected to 10%

rebar corrosion was enclosed with a plastic tank, as shown inrebar corrosion; and Cases 4 and 5 were subjected to 15% rebar

Figure 1(b). This tank was filled with a 5% NaCl solution.

corrosion (see Table 1).

Copper plates were placed around the specimen; these steel
plates were connected to the negative terminal of the power

2.2 Material properties.

supply and used as cathodes. Longitudinal rebars were

UHPC, deformed rebar, and normal concrete were the materials

connected to the positive terminal and used as anodes. Since theused in the experimental study. Initially, the specimens werestudy goal was the flexural strengthening of corrosion-damaged

fabricated with concrete with an average compressive strength

RC bridge piers, we prevented corrosion of the stirrups usingof 25 MPa. The 28-day average tensile strength of concrete wassuitable paints, while the longitudinal rebars were connected todetermined to be 1.7 MPa; the elastic modulus of the normal

the positive terminal of the power supply and used as anodes.

concrete was determined to be 29.5 GPa; and the yield strength

The electric current was 0.5 mA/cm2 during the corrosionof longitudinal reinforcements (D16) and stirrups (D13) was

process. Since corrosion damage at the connection point

determined to be 390 and 383 MPa, respectively. UHPC was

between pier and footing is understood to be more important

used to strengthen two corroded specimens. The mix proportiondue to potential plastic hinge formation, we limited corrosion

of

was

damage to a height of 600 mm above the footing. The time

185:1108:1129:154:12.2 for water: cement: sand: metal fiber:required to achieve the desired rebar corrosion was determinedwater reducing admixture. In the UHPC mix, we used only one

by the following equation:

the

UHPC

used

in

the

experimenttype of steel fiber. The straight fibers were 20 mm in length and

.

𝑡 𝑠𝑒𝑐

0.2 mm in diameter. The 28-day compressive and tensile
strength of UHPC was 143 MPa and 13.7 MPa, respectively.

.
.

(1)

where CF = 96500 C/mol; mloss = required mass loss; nspecimen =Based on the results, the elastic modulus and Poisson ratio,

2; and Mspecimen = 55.8 mol

respectively, were determined to be 51.8 kN/mm2 and 0.22.
Table 1: Experimental cases, corrosion ratio and crack width
Group

Group 1
Group 2

Cases

RemarkCase 1Case 2Sound
10% cor.

Corrosion(%)
010Case 3

10% cor.& retrofitted with UHPC

Case 4
Case 515% cor.
15% cor.& retrofitted with UHPC

- 36 -

ratio

Max.
corrosion
ratio (%)
12.9

Maximumcrack width
0
0.2

10.1

13

0.15

14.7
15.6

20.4
19.5

0.5
0.2

奥村組技術研究年報 No.50

2024 年 9 月

Experimental setup
After the corrosion process, the whole concrete cover in the
corroded area of Cases 3 and 5 was removed by water jet. The
specimens were retrofitted with UHPC layers measuring 50
mm in thickness. The location of the UHPC layers can be seenin Figure 1(c). The experimental setup used for the reverse
cyclic loading can be seen in Figure 1(d). The specimens wereconnected to the rigid foundations of the experiment room witheight threaded rods. Specimens were connected to vertical andhorizontal hydraulic jacks to apply axial and lateral forces. The
loading scheme commenced with the application of an axial
load: The specimens were subjected to a constant axial stress of
1 MPa, which is equivalent to 160 kN. After the application of
axial force, the specimens were subjected to reversed cyclicloading with a drift ratio ranging from 0.25% to 8%, as shownin Figure 2. Load cells were mounted in the hydraulic jacks tomeasure applied loads. Horizontal and vertical displacements
were measured using linear variable displacement transducers
Figure 3. Mass loss of the longitudinal rebars(LVDTs). A total of 27 LVDTs were deployed to measurevertical and horizontal displacement. Strain gauges in the steel

Corrosion processbars were used only in the sound specimen; they were omitted

Following the loading test, the longitudinal rebars in thefrom the other specimens because the rebars were damaged bycorroded area were removed from the concrete to determine theelectric corrosion.

extent of the corrosion. Next, to eliminate the corrosion
products, we submerged the rebars in a 10% diammonium

RESULTS AND DISCUSSION

hydrogen citrate solution at 60 ℃ . Figure 3 presents the
corrosion distribution for Cases 2 to 5. Each rebar was assigned

Corrosion-induced cracking

a unique number. Since the corrosion process in this study was

In the corrosion process, corrosion products appear on the steel

induced by chloride, corrosion occurred in a non-uniformbar, with the amount of corrosion products continuing to grow.

manner. The average mass loss or corrosion ratio was

As the amount of corrosion product increases, it exerts pressure

determined to be 10.1%, 10.0%, and 15.6%, and 14.7% foron the surrounding concrete, generating cracks in the concrete

Case 2, Case 3, Case 4 and Case 5, respectively. In Case 2, thecover. The crack widths of the corroded specimens increased

maximum and minimum corrosion ratios of a single rebar wereconsiderably with the increase in corrosion ratio. In general,

determined to be 12.9% and 6.7%; in Case 3, these were

corrosion cracks emerged parallel to the longitudinal rebars.

determined to be 13.0% and 7.6%. In Case 4, the maximum and

The maximum crack widths recorded for Cases 2, 3, 4, and 5

minimum corrosion ratios were determined to be 20.4% andwere 0.2 mm, 0.15 mm, 0.5 mm, and 0.2 mm, respectively.

11.7%; in Case 5, the maximum and minimum corrosion ratios
were determined to be 19.5% and 11.1%, respectively. The
differences between the maximum and minimum corrosion
ratios in Cases 2, 3, 4, and 5 were determined to be 48%, 42%,43%, and 43%, respectively. Table 1 summarizes the various
corrosion ratios and crack widths. Note that corrosion pit depth
increases with increasing corrosion ratio. The average pit depths
obtained for Cases 2, 3, 4, and 5 were 1.0, 0.9, 1.2 and 1.1 mm,
respectively.

Figure 2. Quasi-static cyclic loading history- 37 -

奥村組技術研究年報 No.50

2024 年 9 月

Figure 4. Hysteretic response of specimens
Hysteretic response

reduced by 9.2% and 6.5%, respectively, compared to the soundFigure 4-5 compares the hysteretic response of corroded andspecimen in the positive and negative loading directions.

sound specimens. The maximum load capacity for the soundHowever, Case 5 demonstrated 20% and 24% higher maximum

specimen in the north (negative direction) and south (positive

load-carrying capacity in the positive and negative loading

direction) was 155 kN and 165 kN, respectively. Case 2

directions compared to the sound specimen.

demonstrated 6% and 3.9% less maximum load capacity(MLC) in the positive and negative loading directions,
respectively. However, Case 3 demonstrated remarkable
improvements in MLC of 24% and 15.5% in the positive andnegative loading directions, compared to the sound specimen.
Compared to Case 2, the MLC increased by 32.3% and 20.1%
in the positive and negative loading direction, respectively. It isnoteworthy that the difference in MLC between the positive andnegative directions was 12.7%, which can be attributed to crosssectional non-uniform corrosion. Case 4 was subjected to 15%
rebar corrosion, while the maximum load-carrying capacity was(a)Figure 5. Backbone curve comparison of the sound,(b)
Figure 6. Comparison of crack pattern of the test specimens at

corroded, and strengthened specimens(a) maximum lateral load and (b) final stage of loading- 38 -

奥村組技術研究年報 No.50

2024 年 9 月

bond between the steel bar and the surrounding concrete. The
increased lateral displacement results in significant spalling of theconcrete cover. This behaviour can be attributed to the buckling of
the longitudinal rebar and corrosion-induced cracking. Horizontal
cracks resulted in flexure dominant failure in the sound andcorroded specimens. The corroded specimens reinforced with the
UHPC layers demonstrated greater control of crack propagation.
Crack widths were notably smaller than with the sound andcorroded specimen. Steel fibers in the UHPC matrix resulted insignificant crack resistance due to bridge effects. In addition, the
UHPC layers provided good confinement and resulted in less rebar
buckling and spalling of the concrete cover. This behaviour helps
achieve significant lateral resistance in UHPC-strengthened
specimens.
Case 5 failed due to insufficient layer thickness, as shown in
Figure 7. The desired layer thickness in this study was morethan 60 mm. However, in Case 5, the average layer thickness
was less than 50 mm. This result indicates that the UFC layers
Figure 7. (a) Photo of failed surface (b) UHPC layer

pushed against the surrounding concrete during reversed cyclic

thickness (c) Failure Analysis

loading, resulting in tension and failure in the surrounding

Cracking patterns and failure modes

concrete. The results suggest that the length along which the

Crack propagation was recorded in every loading cycle. The

tensile force is applied is about three times the thickness of thecracking patterns of the test specimens at maximum lateral load

UFC layer. Based on these observations and depending on UFC

and final stage are shown in Figure 6. As shown in Figure 6, thelayer thickness, the lateral load-resisting capacity of Case 5 cansound and corroded specimens demonstrate flexure dominant

be calculated from the following equation, where X is thefailure. The black and red lines represent cracks in the positive

thickness of the UFC layer and 3X is the influence length. TSC

and negative loading cycles, respectively. In the soundis the tensile strength of concrete and LCL is the length of thespecimen, the first flexural crack appears at the bottom at the

UFC layer.

lateral displacement of 3.5 mm. In the final stage of loading, theflexural cracks are distributed up to 900 mm from the bottom.

Lateral load resisting capacity = 𝑇𝑆𝐶

These flexural cracks are distributed with an approximate

𝑋

3𝑋

𝐿𝐶𝐿

(2)

spacing of 150 mm. The corroded specimens showed fewer
cracks. The reason for this behaviour is the deterioration of theDuctility
Rebar corrosion causes bond loss between rebar and concrete,
reduces rebar cross sections, and generates spalling of the coverconcrete. These factors reduce ductility. In this study, Case 2
and Case 4 demonstrated significantly less ductility than thesound specimen (see Figure 8). Ductility was reduced by 14%
and 17% when Case 2 and Case 4 were subjected to 10% and
15% rebar corrosion, respectively. Interestingly, ductility was
reduced by only about 7% in corroded specimens retrofittedwith UHPC layers. This performance can be attributed to thesteel fibers present in the UHPC and its superior material
properties. Here, ductility is defined as the ratio between

Figure 8. Comparison of ductility

ultimate and yield displacement. Yield displacement is- 39 -

奥村組技術研究年報 No.50

2024 年 9 月

Energy dissipation
We calculated the area in the hysteresis curve in a single loading
cycle to determine the energy dissipation for sound, corroded, andretrofitted RC bridge piers. The energy dissipation capacity
increases with the size of the enclosed area. Figure 10 illustrates
the cumulative energy dissipation of the sound, corroded, andretrofitted specimens. As shown in Figure 10, hysteretic energy
dissipation increases with greater deflection of the test
specimen. Corrosion-damaged specimens retrofitted withUHPC layers demonstrate significantly higher energy
Figure 9. Stiffness degradation of sound and corroded

dissipation than sound and corroded specimens. For example,

specimens

Case 5 demonstrates approximately 100% higher cumulative

determined by visual inspection (considering the change inenergy dissipation capacity than Case 4, when displacement

stiffness); ultimate displacement corresponded to ultimate load

reaches 20 mm. Overall, Case 5 demonstrated 33% higher(85% of MLC).

cumulative energy dissipation than Case 4. On the other hand,
Case 3 displayed 59% higher cumulative energy dissipation
capacity than Case 2.

Stiffness degradation
A major goal of strengthening corroded RC bridge piers withUHPC layers is to improve stiffness. We evaluated the effects

CONCLUSIONSof UHPC layers on the stiffness of the corrosion-damaged

This study proposes a flexural strengthening method forbridge piers. Figure 9 shows the reduction in stiffness of thecorrosion-damaged RC bridge piers using UHPC layers. In our

sound and corroded RC bridge piers during reversed cyclic

study, Case 1 was a sound specimen; Cases 2 and 3 wereloading. Here, stiffness is defined as K = load/deflection. The

subjected to 10% rebar corrosion; Cases 4 and 5 were subjected

stiffness (K) of each cycle is determined by calculating the slope

to 15% rebar corrosion. Cases 3 and 5 were retrofitted withof the lines connecting the highest points of the loading. The

UHPC layers measuring 50 mm in thickness. The following

figure shows the average of both the positive and negative

conclusions can be drawn from our study:

loading cycles. As Figure 9 shows, the magnitude of the1.

Strengthening corrosion-damaged RC bridge piers withstiffness declines with greater deflection. Note that the corroded

UHPC layers is an effective repair option. Strengthened

specimens strengthened with UHPC layers demonstratespecimens demonstrate significantly higher cracking loads,

significantly higher stiffness than the sound and corroded

yielding loads, and MLC. The strengthened specimens

specimens. For example, at a deflection of 3.5 mm, Case 3 andrestored structural performance without affecting original

Case 5 demonstrated about 33% and 31% higher stiffness thangeometry. In Case 3, MLC increased by 24% over thesound specimen.

Case 2 and Case 4, respectively.
2.

RC

bridgepiers

retrofitted

with

UHPC

layersdemonstrated significant crack control and increased
durability.
3.

RC bridge piers strengthened with UHPC layers
demonstrated significantly higher initial stiffness thansound and corroded specimens. In the first loading cycle,
Case 3 and Case 5 demonstrated about 33% and 31%
higher stiffness than Case 2 and Case 4, respectively.

4.

UHPC jacketing improves the displacement capacity or
ductility of corroded specimens. Case 3 displayed 7.3%
higher ductility than Case 2.

Figure 10. Comparison of dissipated energy- 40 -

奥村組技術研究年報 No.50

5.

Energy dissipation capacity increased significantly whencorroded specimens were strengthened with a UHPC
jacket. Case 3 displayed 59% higher cumulative energy
dissipation capacity than Case 2.

【References】
1) Biswas RK, Saito T, Misawa T, Iwanami M. Structural
behavior of severely corroded RC beams retrofitted withUHPC layer: an experimental study. Innov Infrastruct Solut
2023;8:322.
2) Yuan W, Wang X, Guo A, Li C, Dong Z, Wu X. Cyclic
performance of RC bridge piers retrofitted with UHPC
jackets: Experimental investigation. Engineering Structures
3) Ali Dadvar S, Mostofinejad D, Bahmani H. Strengthening of
RC columns by ultra-high performance fiber reinforced
concrete (UHPFRC) jacketing. Construction and Building
Materials 2020;235:117485.
4) JSCE, 2007. Standard Specifications for Concrete Structures- 41 -

2024 年 9 月