May 2023 No.98

Japanese Infrastructure Newsletter

IDI

QUARTERLY
Infrastructure

Development Institute—JAPANCONTENTS
Development of fast-setting UHPFRC for bridge deck overlay

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Bridge Deck Slab Replacement by CAP SLAB

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Infrastructure Development Institute – Japan (IDI)
Plaza Edogawa-bashi 3F. 1-23-6, Sekiguchi, Bunkyo-ku, Tokyo, 112-0014, JAPAN
Tel: +81-3-5227-4107 Fax: +81-3-5227-4109 E-Mail: idi17@idi.or.jp Website: http://www.idi.or.jp/en/Infrastructure Development Institute - Japan

Development of fast-setting UHPFRC for bridge deck overlay
Application examples on site
1. Introduction
There are approximately 730,000 roadbridges in Japan. About half of them will be 50
years old by 2030. Many of these bridges are
suffering from deterioration by fatigue of theslabs due to the heavier repeated wheel runningloads and number of passing vehicles, chloride
attack caused by the application of deicing
agents and damage caused by the freeze-thaw
effect. Deteriorated slabs have been repaired by
the bridge deck overlay method, which involves
removing and replacing the top surface.
However, the conventional material used for the
repair, which is Steel Fiber Reinforced Concrete(SFRC), has poor workability and integrity, anddegradation has recurred.
Therefore, as a material for the bridge
deck overlay method, we developed a fastsetting
Ultra-High-Performance
FiberReinforced
Cement-based
Composite(UHPFRC). UHPFRC is a suitable material for
repairing and reinforcing slabs because it has
high crack resistance and density, and excellent
durability.
As the compressive strength of the fastsetting UHPFRC is quickly developed, thetraffic can be opened in three hours after
pouring the UHPFRC. In addition, its fluidity
can be adjusted to suit the construction area
over the slops up to 10%.
With developing the fast-setting
UHPFRC, the dedicated batcher plant,
transporter and concrete paving machine havebeen also deployed. By means of the abovementioned developments the construction canbe carried out in only one lane at night. This
results in reducing the impact on road users.

2. Outline
In Japan, large-scale renewal projects
are carried out by replacing the slabs and using
the bridge deck overlay method as the slabs ofroad bridges deteriorate with age. However,there were issues such as degradation due toinadequate integration of the SFRC with theexisting slab and the need to verify thesubstructure foundation due to the increased
load on the superstructure.
Recently, UHPFRC, which has highstrength and densification, has been considered
as a replacement material for SFRC to ensure
integrity with the existing slab by using it forthe bridge deck overlay method. However, there
are only a few examples of application of fastsetting UHPFRC.
This paper describes the developmentof fast-setting UHPFRC based on ambient
temperature curing Ultra-high-strength Fiberreinforced Concrete (UFC), and its application
to in-service bridges in order to improve the load
carrying capacity and fatigue durability ofexisting bridge decks. According to theclassification in Japan, the compressive
strength of UFC is 180 N/mm2 or higher, andthat of UHPFRC is 100 N/mm2 or higher(Figure-1).

Figure-1 Classification of UHPFRC in Japan1)1Infrastructure Development Institute - Japanasphalt pavement
waterproof layerwaterproof layer
UHPFRC overlay

Cutting of asphalt pavement
and waterproof layerasphalt pavement

RC slabFigure-2 Outline of the bridge deck overlay method

Although SFRC has been widely used
as a material for the bridge deck overlay method,
there have been reports of lifting anddelamination due to inadequate integration
with the existing deck slab. Therefore, we havedeveloped a fast-setting UHPFRC that can beused for the bridge deck overlay method toimprove durability and integration with theexiting slab.

3. Outline of fast setting UHPFRC(1) Background of material development for thebridge deck overlay method
The deterioration factors of slabs
include fatigue of the slabs due to heavier
repeated wheel running loads and number ofpassing vehicles, as well as lifting, delamination,and graveling of the bridge slabs due to chloride
attack caused by the application of deicing
agents and damage caused by the freeze-thaw
effect (Photo 1).

(2) Outline of the bridge deck overlay method
using UHPFRCUHPFRC is an ultra-high-strength
material and has high crack resistance, andeven if cracks occur, the crack width does notincrease. In addition, since UHPFRC is a densematerial with low permeability, the penetrationof chloride ions and water is limited to thesurface layer. Therefore, there are options foromitting the waterproofing layer, changing to alower grade waterproofing layer than normallyused, or combining with waterproofing asphalt,
which can reduce construction time. Omission
or simplification of bridge waterproofing work
could reduce work process within theconventional regulation time and reduce theregulation time due to construction.
The bridge deck overlay method
involves cutting and grinding the existing slab
surface by approximately 10 mm and adding 50
mm or more of SFRC on top of the existing slab
surface. UHPFR has the same construction
method, but because it is an ultra-high strength
material and there is no need for coarse
aggregate, the reinforcement layer can bethinner than SFRC, and UHPFR also has
superior long-term durability (Fig-2).

Photo-1 Deterioration of the upper surfaceof the slab

For bridges where deterioration islimited to the top surface of the deck, the bridge
deck overlay method is often used to increase
the flexural and shear capacity of the deck.
Where slab deterioration is significant, theexisting slabs are removed and replaced withprecast slabs. This results in significant delaysin the start of construction, especially on
heavily traffic sections near urban areas, due tothe time required to minimize social impacts.
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Infrastructure Development Institute - Japan(3) Fast-setting

UHPFRC

Formulation

andTable-1 Formulation of UHPFRC

Specifications
The basic mix of the fast-setting
UHPFRC is shown in Table 1, and the materials
used are listed in Table 2. The constituent
materials are modified from the "Guidelines forthe Design and Construction of UFC (UFCGuidelines) 2)" published by the Japan Societyof Civil Engineers. Rapid hardener, which is a
powder, is used as a fast-setting material for the
purpose of reducing the regulation time due toconstruction. Table 3 shows the UHPFRC target
performance and measured values.

W/P
Unit weight(kg/m3)
Addition(kg/m3)
(%)
W
P
S
SP* HA** SF
CR
157
4～10
16 210 1327 837 8～30 140* mixing ingredients into water, ** Included in P

Table-2 Materials used in UHPFRC
Type
SymbolMixing waterW
PremixPmaterial
Fine aggregate
S
SP
Admixture
Reinforcing
steel fiber
Rapid hardener
Retardants(a) Accelerated neutralization depth
The flow rate of UHPFRC was set in arange of 150 to 280 mm to suit the slopes of
the construction area over. The flow rate is
set so that the higher the slope, the lower
the flow rate, and has been confirmed to be
used up to 5% on bridges and up to 10% inlaboratory tests. The flow rate of the mortar
was adjusted by setting the amount of highperformance water reducer and retarder tobe added for each ambient temperature
between 5 and 40 degrees Celsius.

SF

Remarks
Tap water
Premix binder for highstrength
Silica sandHigh performance water
reducer
φ0.16×13mm

HA
CR

PowderPowderTable-3 Target performance of UHPFRCUHPFRC(Material age)(b) Compressive strength
The compressive strength of SFRC
used for the bridge deck overlay method has
a management standard value of 24 N/mm2
or more at a given age (usually 3 hours)
according to the Structural Construction
Management Guidelines3) (Management
Guidelines) used by Japanese expressway
companies, and this material also met thisperformance. In addition, the target value of
120 N/mm2 or more was met for compressive
strength at 28 days.

3

Targetvalue

Measuredvalue

Flow (mm)JIS R
5201(Static)

150 to280

185

Air volume (%)

JIS A 1128

4.0 or
less

3.0

24.0
(3hours)

34.8(3hours)120(28days)150(28days)

-

44.3

1.0
(3hours)

1.5(3hours)

1.5(28days)

2.7(28days)

6.0

9.25

Compressive
strength(N/mm2)

JIS A 1108

Static modulus ofelasticity(kN/mm2)

JIS A 1149

Adhesive strength(N/mm2)JIS A 1171

Crack Initiation
Strength(N/mm2)

JIS A 1113

Length change

Test Method
439

Neutralization(mm)Test Method
439

-

0

Apparent diffusion
coefficient of chlorideion(cm2/year)

JCSE-G572
and
JCSE-G574

-

0.032

Less than
211µ250µexpansion

Infrastructure Development Institute - Japan(f) Accelerated neutralization depth
The depth of neutralization after 52
weeks of acceleration test in a 5%
concentration environment was 0 mm for all
sample dimensions, and no neutralization
was observed.

(c) Adhesive strength
UHPFRC showed high adhesivestrength of 2.7 N/mm2 at 28 days of age. In
the bridge deck overlay method, theintegrity of the existing and overlay sections
is important in order to restore and improve
the load-bearing capacity of the slab. The
adhesive strength between the concrete andthe repair material was found to be
sufficient compared to the 1.5 N/mm2 or
more adhesive strength specified in theManagement Guidelines.

(g) Apparent diffusion coefficient of chlorideion
The apparent diffusion coefficient ofchloride ions after 52 weeks of immersion in
a 10% NaCl solution was 0.032cm2/year, alarger value compared to the apparent
diffusioncoefficientofUFC
2(0.0019cm /year), but smaller than that ofordinary concrete (0.14 to 0.9 cm2/year).

(d) Crack initiation strength
The average crack initiation strength
at 28 days was 9.25 N/mm2, which was lower
than the UFC Guidelines average of 11.7
N/mm2. The compressive strength of thismaterial was approximately 130-150 N/mm2,
which was lower than the UFC Guidelines
average of 194 N/mm2. Therefore, the crack
initiation strength is also considered to be
low.
(e) Percentage change in length and mass
Figure 3 shows the measured rates ofchange in length and mass. The rate oflength change was 211 μ expansion strain at
28 days. According to the Management
Guidelines, the dimensional stability of thebridge deck overlay method was defined asa shrinkage rate of 255 μ or less, which
satisfied UHPFRC.

Figure -3 Percentage change in lengthand mass

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Infrastructure Development Institute - Japan

5.900mlane in service(1)Block
Construction day:2021/6/2~3
2
Quantity:185.55m(2)Block
Construction day:2021/6/9~10
2
Quantity: 164.36m(3)Block
Construction date:2021/7/28~29
2
Quantity: 186.81m

Figure-4 The bridge deck overlay area

3. Record of implementation
The reinforced concrete slab (RC slab)
was constructed in the 1960s, and the top
surface of the slab was overlaid by SFRC in
2000. In 2019, a hammer sounding
investigation was conducted on the uppersurface of the subject RC slab. The results
showed that the entire surface of the existingslab had deteriorated. This included lifting at
the interface between the overlay and theexisting slab. It was therefore decided to trial
the fast-setting UHPFRC to repair thedeteriorated areas (536.7 m2) of the first lane
overlay, including the shoulders. (Figure-4).

Figure-5 Machine layout(1) Construction machinery and joints
Figure 5 shows a schematic of themachine layout. After cutting and cleaning thepavement and removing the damaged areas, themachine was placed. The mixer, generator andother equipment were installed in the on-board
plant, and the materials used were measured in
0.5 m3 flexible container packs and placed in anarea where they could be lifted by the crane of atruck-mounted unit (Photo-2).
In previous construction tests on theequipment used, the mixing time for UHPFRC
was about 20 minutes, but because it is fastsetting UHPFRC, the mixer had to be washedafter each batch, resulting in a production cycleof about 40 minutes for each batch. UHPFRC
can be installed in less than 40 minutes, andeven if it were mixed continuously, it would beat the construction joints of each batch.
Therefore, it was decided to install apartition formwork for each batch and to installa construction joint for each block. The
construction joints were treated by applying a
fast-setting
two-component
epoxy
resin
adhesive.

Photo-2 On-board plant5

Infrastructure Development Institute - Japanthe surface between immediately after theoverlay and the asphalt paving. The surface wasobserved prior to the paving and was in goodcondition with no cracking observed (Photo-4).

(2) Construction method
The construction was as follows: First
cut and grind the pavement, then remove andbackfill the deteriorated areas, and finallyoverlay the slab with UHPFRC.
After the pavement was removed, ahammer sounding investigation was performedon the upper surface of the RC slab.
Deteriorated areas, such as uplift anddelamination, were removed by human power
chipping and these sections were repaired withUHPFRC prior to the bridge deck overlay. The
overlay area has a 5% cross slope and is subject
to traffic vibration from adjacent lanes, which
can cause deformation of the materials in theoverlay area. The interface between the existingslab and the UHPFRC was applied a fastsetting two-component epoxy resin adhesive on
all surfaces.
A wheelbarrow was used to transportmaterials due to one-lane work zone. Electric
vibratory trowels and a large engine screed(Photo-3) were used for compaction.

Photo-4 Completion of work

(3) Fluidity
The flow of UHPFRC after mixing was
stable at approximately 220 mm (Figure-6),
regardless of ambient temperature, by
adjusting the amount of high-performancewater reducer and retarder. UHPFRC could becompacted and finished with electric vibratory
trowels for up to 30 minutes after mixing.
Using this construction method, theconstruction time from completion of mixing tooverlaying and finishing was approximately 10
minutes for each batch. Although there was atendency for the flow to drop slightly earlier
during periods of direct sunlight, theinstallation was completed smoothly with no
impact on the job.

Photo-3 Large engine screed

300
260

Block(1)Block
Average① Average
Block
2 (average)
Block(2)Average240

Block3) Average
Block(3)280

Flow (mm)Based on the results of previous
construction tests, the overlay was performed
from the higher slope to the lower slope, taking
into account the deformation characteristics
during the overlay. Especially, the outer
perimeter of the block was carefully compactedwith electric vibratory trowels.
A curing agent that does not interferewith adhesion to the asphalt pavement wasused as a finishing agent in the leveling process,and curing sheet was used to prevent drying of

220
200
180
160
140
120
100
0

15

Time after mixing (minutes)

Figure-6 Elapsed change Mortar flow
overlay method
630

Infrastructure Development Institute - Japan
service expressway, and that fluidity suitablefor construction can be managed by adjusting
the mix to match the ambient temperature.
Based on the above, we believe that the fastsetting UHPFRC can be effectively used as areplacement for the SFRC used in the bridge
deck overlay method.
Design and construction guidelines for
UHPFRC are still under development, andthere is currently no clear design method for
UHPFRC in Japan. Further tests are being
conducted to evaluate the fatigue resistance ofthe fast-setting UHPFRC, which takes
advantage of its high tensile strength, and its
integrity with the existing slab.
In this construction project, theexisting mixer and other equipment were used
to produce UHPFRC, which required a long
mixing time, resulting in a much longer
construction time compared to SFRC. Therefore,
it is essential to develop a mixer and otherequipment with high production capacity, and it
is also important to develop transportation andlaying machines that match the production
capacity. In addition to developing materials, wewill continue to develop equipment such as
mixers.

Compressive strength (N/mm2 )(4) Compressive and Adhesive Strength Test
Results
Samples were taken in the field andtested for compressive strength. Figure 7 shows
the results of the compressive strength tests.
The compressive strength was greater than 24
N/mm2 after 3 hours, 100 N/mm2 after 7 days,
and 140 N/mm2 after 28 days, meeting thetarget strength (120 N/mm2). In addition, theadhesive strength with concrete was confirmed
to be 1.0 N/mm2 or more at 3 hours as a resultof on-site adhesive strength tests conducted inaccordance with the Management Guideline.
180.0
160.0
140.0
120.0
100.0
80.0

Block 1)
Block(1)Block(2)Block (2)Block(3)Block 3)

60.0
40.0
20.0
0.0
0

7

14

21

28

35

Material age (days)

Figure-7 Compressive strength test results
overlay method(5) Results of Overlay Height Check
A 3D laser scanner was used tomeasure fabrication quality after construction
was complete. The bridge deck overlay wascontrolled to within ±10 mm of the design height.
The average thickness was 35.6 mm comparedto the design thickness of 30 mm.

5. Reference
1. Japan Society of Civil Engineers Concrete
Committee. Subcommittee on Structural
Application of Fiber Reinforced Concrete (Phase2) Committee Report Structural Design of Fiber
Reinforced Concrete and its Issues, I-7, Fig. 1.1.1
2. Japan Society of Civil Engineers. Design andConstruction Guidelines for Ultra High Strength
Fiber Reinforced Concrete (Draft), 2004
3. East/Central/West Nippon Expressway Company
Limited:Guidelines
forConstruction
Management of Structures, 2020.

4. Conclusion
It was confirmed that the fast-setting
UHPFRC satisfied the Management Guidelines
standard values for adhesive strength anddimensional stability of cross-sectional repairs
used for the bridge deck overlay, and that thedepth of neutralization and the apparent
diffusion coefficient of chloride ions were lessand more durable than those of ordinary
concrete or SFRC.
The field application of the fast-setting
UHPFRC confirms that construction can becompleted within one-lane restrictions on an in-

6. Conctact Information
Obayashi Corporation,
AOKI Shunji
Civil Engineering Renewal Department
Civil Engineering Technology Divisionaoki.shunji@obayashi.co.jp

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Infrastructure Development Institute - Japan

Bridge Deck Slab Replacement by CAP SLAB
Precast Prestressed Concrete Slab Exclusively Developed for PC I-Girder
3. Detailed Description(1) Structural Design of CAP SLAB
The CAP SLAB has a “cap” shape thatcovers the upper flange on existing PC girders,such that the cap portion functions as a strut
against negative bending moment caused by theslab behavior. This reduces stresses generated
in the slab (Fig-2).

1. Introduction
In recent years, renewal project has
been und-erway in Japan to address aging
expressways. In renewal project of expressway,
vehicle traffic must be restricted in order toreplace deck slabs that directly support vehicleloads.
Therefore, there is a need to develop a
construction method that can shorten the timerequired for the bridge deck replacement. Dueto its structural features, replacing the deckslab of a prestressed concrete (PC) composite Igirder bridge requires a lot of work on site
impacting the traveling public significantly.
2. Outline
The “CAP SLAB” is a precast (PCa)deck panel that has a unique shape at thebottom to cover the top flange of prestressed I
girder (Fig-1).With this shape, the deck panel
and girders can be integrated simply by
installing rebar dowels on the girder top flange
and grouting the gap between the deck panel
and the girders. This minimizes on-site workand greatly improves construction speed. In
addition, the thickness of the deck slab can be
maintained and the road profile does not need
to be raised.
Furthermore, since the CAP SLAB isfabricated in a precast factory, it is easy to adopt
prestressed concrete structures that canenhance the fatigue durability of deck slabs due
to vehicle traffic by stabilizing the quality of thedeck slabs.

10500
9610

This effect limits the increase in slab
thickness and raises the total composite girderheight, minimizing the impact on existing PC
girders and abutment approaches (Fig-3).

445

220

445

Figure-2 Cap shape effect (stress reduction)

G1

G2

G3

Figure-3 Cap shape effect (deck level reduction)

G4

3@2600=7800

Figure-1 CAP SLAB

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Infrastructure Development Institute - Japan(2) Construction①Removal of Existing Deck Slabs
The conventional method requires
concrete removal with water jets to reuse rebars
in existing PC girders for composite section
connections, which is time concerning work inconstruction. By using the cap slab method with
post-installed anchors and non-shrink mortar,
the rebars can be cut by wire saw and slabs canbe removed in short term. Existing slabs were
cut and removed along the upper flange ofexisting PC girders using concrete cutters(vertically) and wire saws (horizontally). Steelbars from the PC girders were also cut (Figs-6
and 7).

For the PCa panel fabrication, theshape, sizes and positions of the upper flange
were premeasured using a 3D scanner on-site
and grouped into several types, which enables
better fit of PCa panels into the existing girders
to maintain quality(Fig-4).

Figure-4 3D scanner

To make a composite section, the PC
girder and slabs were connected by using postinstalled anchors in upper flange and nonshrink mortar filling. The reliability of thedesigned structure was confirmed through fullscale tests. (Figs-5 and 6).
Non-Shrink Mortar

Non-Shrink Mortar

Asphalt
Pavement

Shear Key
Post-Installed Anchor

Figure-6 Cutting and removing
existing deck slabs between girders

Figure-5 Details of joints between the CAP SLAB
and PC girders

Figure-7 Cutting and removing
existing deck slabs on girders

Figure-6 Full-scale structural performance verification
experiment (load transfer verification)

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Infrastructure Development Institute - Japan
4. Anticipated Results②Erection of PCa Panels
The PCa panels were erected (Photo-1),
and a cementitious anchoring system was used
to set shear connector rebars on the top of theupper flanges of existing PC girders. Boundary
surfaces between PCa panels and upper flangesof the main girder were filled with ultra-fastcuring non-shrink mortar. Holes in the PCa
panels for rebars for shear connectors were also
filled with non-shrink mortar.(Figs-8 and 9).

(1) Accelerated Construction
The CAP SLAB method completes thebridge deck replacement three times faster thanthe conventional replacement methods. The
existing bridge removal is simplified byallowing concrete sawing around the girders.
Precast new bridge elements eliminate theneeds for cast-in-place operations on site.
(2) Economic benefits are improved
The PCa panels used on previous
projects increase the total thickness of bridge
decks, requiring the roadway profiles to beraised at each end of projects. The CAP SLAB
method does not change the roadway profile
completely eliminating the works.
(3) Quality and durability are improved
The quality of the precast components
is enhanced because they are manufactured ina controlled factory providing ideal curingconditions
forthe concrete structure.
Prestressing the precast elements adds
durability to the replacement structure.

Photo-1 Erection of PCa panels

6. Record of implementation
The CAP SLAB method is applied to
the Kamitagawa Bridge projects for the Chuo
Expressway in Japan. The Kamitagawa Bridge
is a four-span simply supported bridge
consisting of prestressed I-girders and linkslabs connecting the bridge deck without joints(Photo-2).

Figure-8 Cutting and removing existing
deck slabs on girders
Photo-2 Kamitagawa Bridge
7.Conclusion
Development of new precast deck panels
eliminated a significant amount of on-site work.
Applying the CAP SLAB to highway renewal
projects reduces impacts to the travelling publicduring construction and contributes toextending service life of our infrastructures.

8.Conctact Information
Application：Obayashi Corporation
Engineer : Kenji Mitamura
E-Mail : mitamura.kenji@obayashi.co.jp
TEL : +81-3-5769-1306

Figure-9 Cutting and removing
existing deck slabs on girders
10About IDI and IDI-quarterly
Infrastructure Development Institute-Japan (IDI) is a general incorporated
association operating under the guidance of Ministry of Land, Infrastructure,
Transport and Tourism of Japanese Government.
IDI provides consulting services to facilitate international assistance todeveloping countries, to promote international exchange of information and humanresources, and to support globalization of project implementation systems targeting
both developed and developing countries in the field of infrastructure.
IDI has been publishing a free quarterly journal called “IDI Quarterly”
since1996 to introduce information related to public works and construction
technologies developed in Japan, to foreign countries. We have distributed thejournal to administration officials in more than 90 countries around the world via email.
It will be highly appreciated if you could send us your opinions,impressions, etc. regarding the articles. We also welcome your specific requests
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