PRECAST LINK SLABS FOR JOINTLESS BRIDGE DECKS · PRECAST LINK SLABS FOR JOINTLESS BRIDGE DECKS ... providing good continuity with the bridge deck, but had no compressive ... assistance

PRECAST LINK SLABS FOR JOINTLESS BRIDGE DECKS

Joel Reyes

and

Ian N. Robertson

Research Report UHM/CEE/11-09

December 2011

Prepared in cooperation with the:

State of Hawaii

Department of Transportation Highways Division

and U.S. Department of Transportation Federal Highway Administration

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Technical Report Documentation Page

1. Report No.

2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle

PRECAST LINK SLABS FOR JOINTLESS BRIDGE DECKS 5. Report Date

December 2011

6. Performing Organization Code

7. Author(s)

Reyes, J., and Robertson, I.N. 8. Performing Organization Report No.

UHM/CEE/11-09

9. Performing Organization Name and Address Department of Civil and Environmental Engineering

University of Hawaii at Manoa

2540 Dole St. Holmes Hall 383

Honolulu, HI 96822

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

12. Sponsoring Agency Name and Address Hawaii Department of Transportation

Highways Division

869 Punchbowl Street

Honolulu, HI 96813

13. Type of Report and Period Covered

Final

14. Sponsoring Agency Code

15. Supplementary Notes

Prepared in cooperation with the U.S. Department of Transportation, Federal Highway Administration

16. Abstract

The purpose of this study of high‐performance fiber‐reinforced cementitious composite (HPFRCC) reinforced with glass fiber reinforced polymer (GFRP) bars was to investigate its use as link slabs to replace the expansion joints commonly found in bridge decks.

Numerous small scale test specimens and a full scale specimen test were conducted to characterize the performance of HPFRCC with GFRP reinforcing bars. After the small scale tests were completed, a full scale bridge expansion joint specimen was constructed to test the strain capabilities of the HPFRCC as a link slab. The full scale bridge expansion joint specimen emulated an expansion joint condition of a composite steel girder to concrete deck slab section. The link slab was 90 inches wide by 3 inches thick with an unbonded length of 6 feet and was recessed into the top 3 inches of a 9 inch thick deck slab. #3 GFRP reinforcement bars were placed at mid‐depth of the link slab at 6 inches on center and the ends were cast in to the cast‐in‐place concrete deck. The slab was then subjected to cyclic axial strains in both tension and compression and later in direct tension until failure. It was found that the cast‐in‐place link slab had the advantage of providing good continuity with the bridge deck, but had no compressive strain capacity.

In order to improve the constructability of the link slab, and to provide compressive strain capacity after installation, two specimens were constructed with pre‐cracked HPFRCC link slabs. The anchorage at the ends of the link slab was changed for the two specimens to try and simplify the installation process. The precast link slabs were able to accommodate limited compressive strains, and the same tensile strain as the cast‐in‐place link slab. Failure occurred due to rupture of the anchorage at the ends of the link slab.

17. Key Words

Fiber Reinforced Cementitious Composite, Bridge Joints, Ductile Concrete, Precast Link Slabs

18. Distribution Statement

19. Security Classif. (of this report)

Unclassified 20. Security Classif. (of this page)

Unclassified 21. No. of Pages

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

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ABSTRACT

The purpose of this study of high-performance fiber-reinforced cementitious

composite (HPFRCC) reinforced with glass fiber reinforced polymer (GFRP) bars

was to investigate its use as link slabs to replace the expansion joints commonly

found in bridge decks.

Numerous small scale test specimens and a full scale specimen test were

conducted to characterize the performance of HPFRCC with GFRP reinforcing

bars. After the small scale tests were completed, a full scale bridge expansion joint

specimen was constructed to test the strain capabilities of the HPFRCC as a link

slab. The full scale bridge expansion joint specimen emulated an expansion joint

condition of a composite steel girder to concrete deck slab section. The link slab

was 90 inches wide by 3 inches thick with an unbonded length of 6 feet and was

recessed into the top 3 inches of a 9 inch thick deck slab. #3 GFRP reinforcement

bars were placed at mid-depth of the link slab at 6 inches on center and the ends

were cast in to the cast-in-place concrete deck. The slab was then subjected to

cyclic axial strains in both tension and compression and later in direct tension until

failure. The link slab’s strain capabilities and distribution of microcracking were the

primary focus of the full scale test. It was found that the cast-in-place link slab had

the advantage of providing good continuity with the bridge deck, but had no

compressive strain capacity.

In order to improve the constructability of the link slab, and to provide

compressive strain capacity after installation, two specimens were constructed with

pre-cracked HPFRCC link slabs. The anchorage at the ends of the link slab was

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changed for the two specimens to try and simplify the installation process. The

precast link slabs were able to accommodate limited compressive strains, and the

same tensile strain as the cast-in-place link slab. Failure occurred due to rupture of

the anchorage at the ends of the link slab.

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ACKNOWLEDGEMENTS

This report is based on a Masters’ Plan B report prepared by Joel Reyes under

the direction of Dr. Ian Robertson at the Department of Civil and Environmental

Engineering at the University of Hawaii at Manoa. The authors wish to thank Dr. Lin

Shen and Dr. Tianwei Ma for their assistance in reviewing this report.

The authors also wish to thank Dr. Gregor Fischer and Bryan Lum for their

assistance with the design, testing, and analysis of the link slab test specimens.

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Table of Contents

1 Introduction ................................................................................................................ 1

1.1 Background ......................................................................................................... 1

1.2 Jointless Bridge Decks ....................................................................................... 3

1.3 Previous Research ............................................................................................. 4

2 Materials .................................................................................................................... 7

2.1 High-Performance Fiber-Reinforced Cementitious Composite (HPFRCC)

Polymer.......................................................................................................................... 7

2.2 Glass Fiber Reinforced Polymer(GFRP) Bars .................................................. 10

2.3 Test Setup ........................................................................................................ 11

2.4 Measurement Devices ...................................................................................... 14

2.5 Objective ........................................................................................................... 18

3 Approach .................................................................................................................. 21

3.1 Test Specimens #1 ........................................................................................... 21

3.2 Test Specimens #2 ........................................................................................... 23

3.3 Test Specimens #3 ........................................................................................... 29

4 Analysis .................................................................................................................... 33

4.1 Specimen #1 ..................................................................................................... 33

4.2 Specimen #2 ..................................................................................................... 41

4.3 Specimen #3 ..................................................................................................... 47

5 Discussion ................................................................................................................ 55

5.1 Specimen #1 ..................................................................................................... 55

5.2 Specimen #2 ..................................................................................................... 57

5.3 Specimen #3 ..................................................................................................... 59

6 Conclusions/Recommendations .............................................................................. 61

7 References ............................................................................................................... 63

8 Appendix A: Test Photos ......................................................................................... 66

8.1 Specimen #1 Observation Photo's .................................................................... 67



9 Appendix B: Test Specimen Layout ......................................................................... 76

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List of Figures

Figure 1-1: Neoprene pad supporting concrete girder ...................................................... 1

Figure 1-2: Typical Bridge Joint Sealer(Left), Cracks in Joint Sealer(Right) ..................... 2

Figure 1-3: Corrosion in pier or support beam .................................................................. 3

Figure 1-4: Bridge deck cold joint ...................................................................................... 3

Figure 2-1: Portland Cement(Left), #90 Orange County Silica Sand(Right) ..................... 8

Figure 2-2: #90 Silica Sand(Left), Polyethylene Fibers(Right) .......................................... 8

Figure 2-3: Polycarboxylic Ether Admixture(Left), Methyl Cellulose Admixture(Right) ..... 8

Figure 2-4: Hobart Mixer(Left), HPFRCC mix(Right) ......................................................... 9

Figure 2-5: #3 Glass Fiber Reinforced Bars .................................................................... 10

Figure 2-6: Framing Sections .......................................................................................... 11

Figure 2-7: Reinforced concrete slab viewed from cantilevered end of the girder

support(Left), Outer steel girder viewed from fixed end(Right) ....................................... 12

Figure 2-8: Girder support anchored to concrete slab below .......................................... 12

Figure 2-9: Expansion joint and girder gap viewed from outside(Left), viewed from

inside(Right) .................................................................................................................... 13

Figure 2-10: Unmounted clevis attached to actuator above ............................................ 14

Figure 2-11: Rectangular steel tubing viewed from above(Left), LVDT's measuring

displacement of steel section .......................................................................................... 15

Figure 2-12: Anchoring of the steel tubing at the bonded and unbonded sections ......... 15

Figure 2-13: LVDT measuring gap displacement ............................................................ 16

Figure 2-14: LVDT measuring steel girder displacement ................................................ 16

Figure 2-15: Strain Gauges ............................................................................................. 17

Figure 2-16: Sensor Layout ............................................................................................. 17

Figure 2-17: Sensor Layout ............................................................................................. 18

Figure 2-18: Specimen Frame Diagram .......................................................................... 19

Figure 3-1: Specimen Frame Diagram ............................................................................ 21

Figure 3-2: GFRP bar layout(Left), Bonded section and anchor hooks(Right) ................ 22

Figure 3-3: Debonding plexiglass .................................................................................... 22

Figure 3-4: Finished link slab and wood forming(Left), Link slab surface(Right) ............. 23

Figure 3-5: GFRP Layout and Formwork ........................................................................ 24

Figure 3-6: Precracking ................................................................................................... 24

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Figure 3-7: Precracking Setup ........................................................................................ 25

Figure 3-8: Anchors and Dowels ..................................................................................... 27

Figure 3-9: Vertical Dowels ............................................................................................. 28

Figure 3-10: Horizontal Dowels ....................................................................................... 28

Figure 3-11: Dowel Layout .............................................................................................. 29

Figure 3-12: Hydraulic Actuator ...................................................................................... 30

Figure 3-13: Link Slab ..................................................................................................... 30

Figure 3-14: Precracking Setup ...................................................................................... 31

Figure 3-15: Installed HPFRCC Link Slab ....................................................................... 32

Figure 4-1: Specimen #1 Actuator Load vs Cycles ......................................................... 33

Figure 4-2: Specimen #1 Actuator Load vs Displacement .............................................. 34

Figure 4-3: Specimen #1 Unbonded Section Stress vs Strain ........................................ 36

Figure 4-4: Specimen #1 Bonded Section Stress vs Strain ............................................ 37

Figure 4-5: Specimen #1 Unbonded Section vs Gap ...................................................... 39

Figure 4-6: Specimen #1 Bonded Section vs Gap Displacement ................................... 40

Figure 4-7: Specimen #2 Actuator Load vs Cycles ......................................................... 41

Figure 4-8: Specimen #2 Actuator Load vs Displacement .............................................. 42

Figure 4-9: Specimen #2 Unbonded Section Stress vs Strain ........................................ 43

Figure 4-10: Specimen #2 Bonded Section Stress vs Strain: Load to Failure ................ 44

Figure 4-11: Specimen #2 Unbonded Section Displacement vs Gap ............................. 45

Figure 4-12: Specimen #2 Bonded Section Displacement vs Gap: Load to Failure ....... 46

Figure 4-13: Specimen #1 Actuator Load vs Cycles ....................................................... 48

Figure 4-14: Specimen #3 Actuator Load vs Displacement ............................................ 49

Figure 4-15: Specimen #3 Unbonded Section Stress vs Strain ...................................... 50

Figure 4-16: Specimen #3 Bonded Section Stress vs Strain .......................................... 51

Figure 4-17: Specimen #3 Unbonded Section vs Gap .................................................... 52

Figure 4-18: Specimen #3 Bonded Section vs Gap ........................................................ 53

Figure 5-1: Specimen #1 Failure Diagram ...................................................................... 55



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List of Tables

Table 1: HPFRCC Mixture Percentage by Weight ............................................................ 9

Table 2: Specimen #2 Precracking ................................................................................. 26

Table 3: Specimen #3 Precracking ................................................................................. 32

Table 4: Measuring Device Abbreviations and Descriptions ........................................... 79

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1

1 Introduction

1.1 Background

Many current highway bridges are constructed with composite concrete slabs

on either steel or concrete girders simply supported on piers or bents.

Though piers or bents can be constructed of different materials such as

concrete or steel, the connections used to support the bridge deck in most

cases are still made of steel pin rollers and in some cases neoprene pads.

The following figures 1-1 thru 1-3 are examples from a typical bridge joint

located on the H1 freeway viaduct in Hawaii. Figure 1-1 shows the concrete

girder resting on a steel plate and neoprene pad.

Figure 1-1: Neoprene pad supporting concrete girder

These connections are effective in that they allow deflection of the bridge

deck during thermal expansion, shrinkage, creep as well as the onset of daily

service loads. However, these connections require a gap in the concrete

which makes it vulnerable to corrosive chemicals and debris limiting the

service life of not only the connection itself but the bridge deck it supports. As

can be seen in the Figure 1-2, these joints are typically filled with a joint

sealer which compress and expand depending on the length of the bridge

deck at any given time to alleviate rain run-off and debris from damaging the

2

concrete and support bearing below. Over time these joint sealers lose

effectiveness when cracks develop as the compound loses ductility.

Figure 1-2: Typical Bridge Joint Sealer (Left), Cracks in Joint Sealer (Right)

Under normal working conditions, aggregates and debris are common in and

around the joint sealers (Figure 1-2). If these cracks are not controlled and

allowed to propagate and expand, debris can be wedged within the joint and

rain run-off can seep through the sealer decreasing the effectiveness of the

bridge joint. Therefore, maintenance of these joints, though costly and

frequent, is important to the service life of the structure.

As can be seen in Figure 1-3, corrosion is not only limited to the pin or

neoprene pad support but can also corrode the reinforcement within the pier

or supporting beam possibly compromising its structural integrity.

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Figure 1-3: Corrosion in pier or support beam

As stated in the report by Lepech and Li, as recently as 1998, the American

Society of Civil Engineers assigned grades of D- to America's roads and C-

to bridges. In 2002, the USDOT reported that over half of roads and bridges

are in fair, mediocre, or poor condition. It is for these reasons that we aim to

effectively increase the overall service life of local and national road and

bridge infrastructures.

1.2 Jointless Bridge Decks

One way of reducing the maintenance of bridge joints is by removing them

completely and replacing them with link slabs (Figure 1-4).

Figure 1-4: Bridge deck cold joint

Link slabs are composed of high-performance fiber-reinforced cementitious

composite (HPFRCC) and glass fiber reinforced polymer (GFRP) bars.

4

Unlike conventional concrete which produces localized cracks under tension

loads, link slabs are designed to induce multiple micro cracks along its entire

length. Lepech and Li reported these cracks to open to a maximum of

between 50µm and 70µm during early strain hardening(i.e. below 1% tensile

strain) and remain at that width under additional tensile strain to failure. The

link slab must be of sufficient length that the sum of micro cracks within the

link slab is about equal to the expected change in joint width. A recent report

submitted to the Michigan Department of Transportation recommends that

the unbonded length of the link slab equal a minimum 5% of the girder span

in order to reduce stiffness (Li and others, 2003).

Li and others (2003) also recommends 2.5 inches of clear cover to control

crack widths. In practical applications, the stress required to induce cracking

in a slab with a clear cover of 2.5 inches (about 5 inch thick slab) may not

occur. Therefore, a 3 inch slab thickness and an unbonded link slab length of

6 feet was used. Based on the assumption that the unbonded length of the

link slab should equal a minimum 5% of the girder span, the 6 foot unbonded

length correlates to a maximum girder span of 120 feet.

1.3 Previous Research

The durability of reinforced concrete is greatly dependent on the size and

quantity of the formation of cracks. These cracks allow chlorides and other

deicing materials to permeate through the concrete and corrode the steel

reinforcement. To minimize permeability and increase durability, various

codes set limits on the maximum crack widths. ACI 222 limits the crack width

to 0.33mm for exterior members and 0.41mm for interior members. ACI 224

limits this further in high corrosive environments such as areas with high

humidity or areas exposed to sea water. These can range from 0.41mm in

dry areas to a maximum of 0.10mm in areas which retain water (Ahmed and

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Mihashi, 2007). Ahmed and Mihashi (2007) found that under service loads,

the bottom of the HPFRCC beams tested had an average crack width of

10mm. Because crack width is well controlled in HPFRCC even at service

loads, the material can be used in lieu of reinforced concrete in most

applications with the benefit of increased durability.

Ahmed and Mihashi (2007) also summarized various research done on

HPFRCC including the permeability characteristics of cracked HPFRCC.

Research found that under a tensile strain of 1.5%, cracked HPFRCC had

about the same permeability before the onset of cracking. At these

conditions, HPFRCC had closely spaced crack widths of about 0.06mm

which is compared to conventional reinforced concrete that had crack widths

varying between 0.15mm and over 2.5mm. It is apparent, that HPFRCC is

much less permeable than conventional concrete.

The deformation of HPFRCC is a material property and independent of the

gage length of the reinforcement fiber (Li and Fischer). Li and Fischer

reported that HPFRCC has an ultimate strain of 5-8Mpa and a strain capacity

of 3-5%. These HPFRCC mixtures typically consist of cement, sand, fly ash,

water, additive, and 1.5-2% of polymeric fibers, such as polyethylene.

Polyethylene fibers are different than others available, in that the fiber resist

forces exclusively by its frictional bond (Li and Fischer). Essentially, the fiber

continues to resist load even after complete debonding until it reaches a

peak tensile load and then suddenly decreases in capacity until the fiber is

completely pulled out.

Because HPFRCC uses larger quantities of cement and water than

conventional concrete, higher shrinkage can be observed (Ahmed and

Mihashi, 2007). However, when a restrained shrinkage test was performed,

crack widths remained below 0.050mm.

6

Similar to conventional concrete, the effectiveness of HPFRCC is dependent

on the mix design. In a link slab test performed by Li and others (2003), a mix

design using 2% fibers and 1.0 cement, 0.53 water, 0.8 sand, 1.2 type F fly

ash, and 0.03 super-plasticizer proportioned by weight was used. These

properties were chosen because the HPFRCC mix was found to have good

workability, had a compressive stress of about 8700psi after curing, and a

tensile strain capacity of 3% at 28days.

Although extensive tests have been performed to determine the shrinkage as

well as other material properties, it is important to note that majority of the

tests are not standardized and the HPFRCC mix design usually vary

between research done.

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2 Materials

2.1 High-Performance Fiber-Reinforced Cementitious Composite (HPFRCC)

Polymer

High-Performance Fiber-Reinforced Cementitious Composite (HPFRCC)

polymer is a cement based material that has the ability to strain harden in

tension. That is, it has the ability to undergo large tensile strains caused by

both tensile and bending stresses. Under these tensile and bending stresses,

multiple micro cracks are induced allowing the material to elongate. For link

slab applications as well as the experiment reported herein, Engineered

Cementitious Composite (ECC) is ideal. ECC is a type of HPFRCC that has

about the same compressive capabilities of conventional concrete. Within

this report, ECC and HPFRCC shall be used interchangeably but shall both

refer to ECC.

HPFRCC is able to strain harden because it does not use coarse aggregate

but instead the concrete is held together and strengthened by small fibers.

When the concrete reaches its elastic limit, the fibers slip between the many

microscopic cracks, this action is referred to as fiber bridging. Strain

hardening occurs when the peak bridging stress between fibers in a

developing crack is larger than stress required to first initiate cracking (Li and

Fischer). This ensures that the stress applied prior cracking can be carried by

the embedded fibers. This allows the internal forces to be evenly distributed

rather than become localized as what is expected with conventional

concrete.

The HPFRCC mix used in the experimental tests was comprised of Portland

Cement (Figure 2-1), #90 Silica Sand (Figure 2-1 and Figure 2-2), fly ash,

water, Polyethylene Fibers (Figures 2-2), Polycarboxylic Ether (Figure 2-3),

and Methyl Cellulose admixtures (Figures 2-3).

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Figure 2-1: Portland Cement(Left), #90 Orange County Silica Sand(Right)

Figure 2-2: #90 Silica Sand(Left), Polyethylene Fibers(Right)

Figure 2-3: Polycarboxylic Ether Admixture(Left), Methyl Cellulose Admixture(Right)

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The percentage by weight for each of these components used the HPFRCC

mix are recorded in Table 1.

Table 1: HPFRCC Mixture Percentage by Weight

Material Percentage by

Weight

Portland Cement 27.80%

#90 Silica Sand 22.25%

Fly ash 33.33%

Water 15.00%

Polyethylene Fibers 1.23%

Polycarboxylic Ether (Admixture)

0.36%

Methyl Cellulose (Admixture)

0.03%

The HPFRCC mix used in the experiment was mixed in a Hobart mixer

(Figure 2-4).

Figure 2-4: Hobart Mixer (Left), HPFRCC mix (Right)

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2.2 Glass Fiber Reinforced Polymer (GFRP) Bars

Glass Fiber Reinforced Polymer (GFRP) was the primary reinforcement used

in the longitudinal and transverse direction of the HPFRCC link slabs (Figure

2-5).

Figure 2-5: #3 Glass Fiber Reinforced Bars

Section 3 further discusses the reinforcement layout for each specimen. This

type of reinforcement was chosen because it is non-corrosive and is equal to

or greater in tensile strength to structural steel, and can be used in most of

the same applications. One of the major advantages of GFRP bars is that it

has a much lower modulus of elasticity compared to that of steel. This means

less tensile force is required to deform the bars and the micro cracks are able

to develop. For the application of jointless bridge decks, because higher

elongations are expected, the unbonded length of the link slab must be of

adequate length to reduce the strain in the concrete to within the elastic

region of the GFRP bars.

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2.3 Test Setup

The full scale test specimen was constructed as shown in Figure 2-6.

Figure 2-6: Framing Sections

The composite bridge deck is comprised of a 9 inch thick reinforced concrete

slab built on 2 W-shaped hot-rolled steel girders. To ensure a composite

action between the concrete slab and steel girders, (2)3/4"x4" studs were

welded to the girder every 12 inches. Figure 2-7 shows the reinforced

concrete slab and the attached steel girders below.

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Figure 2-7: Reinforced concrete slab viewed from cantilevered end of the girder

support(Left), Outer steel girder viewed from fixed end(Right)

The link slab is located far enough above the girder support, which acts as

the center of rotation, that the induced tension and compression loads in the

link slab can be assumed to be purely axial. To mimic service loads in the

test specimen, the girder was cantilevered out on one side and was attached

to a hydraulic actuator that applied a gravity tensile and compression loads.

To ensure the entire actuator load is reflected in the recorded stresses in the

link slab, the adjacent girder was anchored to the 2'-0" concrete slab below

to minimize movement (Figure 2-8).

Figure 2-8: Girder support anchored to concrete slab below

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Figure 2-9 shows the 1 inch expansion joint in the reinforced concrete slab

as well as the gap between the girder supports. These supports are welded

to the W-shape section below and reinforced with steel plates which acts as

pin connection. The expansion joint was measured and compared to the

elongation in the link slab to evaluate its effectiveness.

Figure 2-9: Expansion joint and girder gap viewed from outside(Left), viewed from

inside(Right)

Figure 2-10 shows the clevis and mounting point used to attach the actuator

to the test specimen. As the actuator deflects upwards, it induced a

compressive force in the link slab. Similarly, a downward deflection

correlated to a tensile force in the link slab

14

Figure 2-10: Unmounted clevis attached to actuator above

2.4 Measurement Devices

To measure the displacements in the link slab and test specimen, a total of 8

Linear Variable Displacement Transducers (LVDT) were used. The overall

elongation of the link slab was captured using 4 relatively undeformable

rectangular steel tubes, as shown in Figure 2-11 and 2-12. These rectangular

tubes are anchored on one side and are free to slide on the opposing side,

which is measured with an LVDT. Two of these steel LVDT combinations

were used to measure the elongation from unbonded section of the link slab

to the opposing unbonded section, and two were used to measure the

elongation from the end of the bonded section on one side to the end of the

bonded section on the opposing side.

15

Figure 2-11: Rectangular steel tubing viewed from above(Left), LVDT's measuring

displacement of steel section

Figure 2-12: Anchoring of the steel tubing at the bonded and unbonded sections

The LVDT shown in Figure 2-13 measured the change in gap displacement

of the expansion joint. The values obtained from the LVDT represented the

true displacements of the reinforced concrete slab. The measured value of

change in gap length was used to evaluate the effectiveness of the link slab.

16

Figure 2-13: LVDT measuring gap displacement

The LVDT shown in Figure 2-14 measured the displacement of the steel

girders. The measured values were compared to gap displacement to ensure

composite action concrete slab and steel girders.

Figure 2-14: LVDT measuring steel girder displacement

In addition to the LVDT's, 4 strain gauges on the top and bottom flanges of

the girders near the actuator were used to verify equal distribution of loads

on each girder (Figure 2-15).

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Figure 2-15: Strain Gauges

Figures 2-16 and 2-17 show the detailed locations of the LVDT's and strain

gauges in and around the test specimen.

Figure 2-16: Sensor Layout

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Figure 2-17: Sensor Layout

2.5 Objective

The purpose of the research was to test 3 different link slab configurations

and determine if any or all could be implemented in local and national

highways. These configurations to be discussed later in more detail are as

follows:

1. Cast-in-place HPFRCC

2. Precast HPFRCC dowelled horizontally and vertically

3. Precast HPFRCC dowelled vertically only

Figure 2-18 shows a general specimen and frame configuration. Though

each test configuration is constructed differently, all of them have a 1 foot

bonded section at each end and a 6 foot unbonded section.

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Figure 2-18: Specimen Frame Diagram

The basis on determining the effectiveness of these link slabs were as

follows:

The gap displacement and unbonded displacement should be

about equal meaning the unbonded section is acting elastically

The link slab remains elastic over numerous cycles

The link slab retains its compressive capacity

Tensile failure occurs well beyond the actual loads expected

Micro cracks remain uniform over the entire debonded section and

does not localize.

20

21

3 Approach

3.1 Test Specimens #1

Specimen #1 was a 7'-6" wide 3 inch thick cast in place HPFRCC link slab

reinforced with #3 GFRP bars spaced 6 inches on center in the longitudinal

and transverse directions. For this specimen, the 2'-0" bonded section on

both sides of the link slab were cast simultaneously into the reinforced

concrete slab. This setup would only be appropriate for new construction or

major reconstruction where the use of a link slab is predetermined in design.

One advantage of using a cast-in-place HPFRCC link slab is that the GFRP

bars of the link slab are well bonded to the reinforced concrete and hooked

bars can used in the 1'-0" bonded section. For this specimen, each GFRP

bar were doweled to the reinforced concrete with (2) #3 steel anchor

hooks(Figure 3-1). This ensured the link slab was well bonded to the

reinforced concrete. With the cast-in-place HPFRCC link slab, it was

expected that there would be little slippage of the GFRP bar within the

bonded section.

Figure 3-1: Specimen Frame Diagram

22

Figure 3-2 shows the GFRP bars anchored with (2) #3 steel anchor hooks.

These hooks were placed during the casting of the reinforced concrete and

were dried and cured to the full capacity of the concrete before the HPFRCC

link slab was poured. In addition, the bonded section was roughened which

contributed to the bonding of the link slab to the reinforced concrete.

Figure 3-2: GFRP bar layout(Left), Bonded section and anchor hooks(Right)

Figure 3-3 shows the plexiglass used to debond the HPFRCC link slab from

the concrete below. This ensured a smooth surface for the link slab to

expand and contract during loading.

Figure 3-3: Debonding plexiglass

Figure 3-4 (Left) shows the finished link slab and the wood forming built

around the reinforced concrete. The self consolidating HPFRCC mix was

23

rodded to remove any air bubbles to ensure a homogenous mix well bonded

to the GFRP bars. As can be seen in Figure 3-4 (Right), the link slab could

not be trowelled to a smooth surface. In practical applications, this is not a

major concern as most roadways are roughened or saw cut for daily traffic.

Figure 3-4: Finished link slab and wood forming(Left), Link slab surface(Right)


Specimen #2 was a 3'-9" wide 3 inch thick pre-cast HPFRCC link slab. Due

to the long setting and curing time of HPFRCC, this type of link slab would be

more appropriate for reconstruction and renovations rather than new

construction. This specimen used the same HPFRCC mix design as

specimen #1, described in section 2.1. The link slab was reinforced with #2

GFRP bars spaced 3 inches on center in the longitudinal direction and #2

GFRP bars spaced 6 inches on center in the transverse direction. Smaller,

closer spaced GFRP bars were used to better control localized cracking. As

can be seen in Figure 3-5, the formwork was laid on a flat surface and was

designed to allow the GFRP bars to extend out of the formwork 2'-0" on both

sides of the slab.

24

Figure 3-5: GFRP Layout and Formwork

The link slab was allowed to properly set and cure before being removed

from the formwork. Before being grouted and doweled to the reinforced

concrete for testing, the specimen was first precracked (Figure 3-6), to

induced micro cracking which allowed some compressive strain capacity.

Precracking was done to the middle 6'-0" of the slab, which was the

unbonded section of the link slab when fully installed.

Figure 3-6: Precracking

25

Precracking was performed in 1'-0" increments to minimize the possibility of

localization. To achieve this, 3 concrete blocks weighing about 4000lbs each

were placed on 2- 4x4 timbers spaced 3'-0" apart (Figure 3-7). This induced

a uniform moment within the 1'-0" spaced supports enough to precrack the

concrete. This procedure was repeated on both sides of the link slab.

Figure 3-7: Precracking Setup

The unbonded length of specimen #2 was measured during precracking and

reported in Table 2. After precracking of each 1 foot section of the bottom

26

surface of the link slab, the elongation of each side of the link slab was

measured and reported as Bottom I and Bottom II. The process was then

repeated on the top surface of the link slab and the elongation of each side

was measured and reported as Top I and Top II. The total elongation and

strain capacity of the unbonded section of the link slab was determined by

the averaging the elongation of the link slab after the last 1 foot segment

(Top I and Top II).

Table 2: Specimen #2 Precracking

Before Crack-

ing

After Precracking Section from: Δ

1'-2' 2'-3' 3'-4' 4'-5' 5'-6' 6'-7'

Bottom I 72 72.017 72.056 72.067 72.076 72.077 72.066 0.017

Bottom II 72 72.009 72.052 72.068 72.088 72.083 72.065 0.009

Top I -- 72.033 72.039 72.066 72.068 72.087 72.089 0.089

Top II -- 72.022 72.036 72.037 72.039 72.066 72.066 0.066

Average = 0.077

Avg ∆/L = 0.107%

Specimen #2 was doweled as shown in Figure 3-8. A total of 14- #4 steel

bars spaced 3 inches apart provided vertical and horizontal anchorage. Each

dowel was 6 inches long and was embedded about 3 inches into the

reinforced concrete below. In addition, the #2 GFRP bars were doweled 2'-0"

horizontally into the reinforced concrete. To ensure an adequate 1'-0"

bonded region, both the link slab and the reinforced concrete were

roughened and bonded using Non-Shrink Precision Grout, as manufactured

by Quikrete.

27

Figure 3-8: Anchors and Dowels

The #4 vertical anchors were installed as shown in Figure 3-9. 5/8" diameter

holes were drilled to a minimum depth of 3 inches into the reinforced

concrete below, equivalent to about 6 or 7 inches from the top of the link

slab. The #4 bars were placed in the holes and grouted using Non-Shrink

Precision Grout, as manufactured by Quikrete, and trowelled to a flat surface.

28

Figure 3-9: Vertical Dowels

Figure 3-10 shows the horizontal GFRP bars dowelled into the reinforced

concrete. At these locations, the reinforced concrete was dry cut with a

diamond saw blade and chipped out. The reinforced concrete was chipped

enough that there was at least 1/2" clearance between the reinforced

concrete and the GFRP bar on all sides. This ensured the GFRP bars were

adequately coated with grout. The GFRP bars were grouted with Non-Shrink

Grout, as manufactured by Quikrete and trowelled to a flat surface.

Figure 3-10: Horizontal Dowels

29


Specimen #3 was constructed the same way as specimen #2 as described in

section 3.2. However, the GFRP bars do not extend beyond the extents of

the link slab. Instead, the link slab was anchored to the reinforced concrete

by 21-#4 steel bars as shown in Figure 3-11. Similar to Specimen #2, each

dowel was 6 inches long and was embedded about 3 inches into the

reinforced concrete below. The 1'-0" bonded section was also roughened on

the link slab and reinforced concrete surfaces and bonded with Non-Shrink

Precision Grout, as manufactured by Quikrete.

Figure 3-11: Dowel Layout

Similar to specimen #2, the link slab was precracked to allow some

compressive strain capacity. However, to increase the compressive strain

capacity beyond that of Specimen #2, the precracking load was increased.

To apply a higher load, a 300Kip hydraulic actuator applied a point load to

the simply supporting a W-beam, and the link slab was placed under one of

the W-beam supports (Figure 3-12 and 3-13).

30

Figure 3-12: Hydraulic Actuator

Figure 3-13: Link Slab

Precracking was performed in 1'-0" increments to minimize the possibility of

localization. To achieve this, the load from the W-beam applied a point load

on the link slab which was simply supported on 4x4 timbers placed about 2'-

0" apart (Figure 3-14). This induced a moment within the 2'-0" spaced

supports enough to precrack the concrete. This procedure was repeated on

both sides of the link slab.

31

Figure 3-14: Precracking Setup

The actuator load was incrementally increased to just before localization

could be visually seen in order to maximize the effects of precracking. The

results from the precracking were reported in Table 3. Measurements of the

unbonded section elongation on both sides of the link slab were taken after

precracking of 1/2 length, full length and at the full length of the opposite

surface. The total elongation and strain capacity of the unbonded section of

the link slab was determined by averaging the elongation at Side I and Side

II.

32

Table 3: Specimen #3 Precracking

Before

Cracking

After Precracking Section at: Δ

1/2 Length Full Length Opposite Side

Side I 72 72.036 72.057 72.132 0.132

Side II 72 72.009 72.028 72.115 0.114

Average 0.123

Avg ∆/L = 0.171%

Similar to Specimen #2, the #4 vertical anchors were installed by drilling 5/8"

diameter holes to a minimum depth of 3 inches into the reinforced concrete

below, equivalent to about 6 or 7 inches from the top of the link slab. The #4

bars were placed in the holes and grouted using Non-Shrink Precision Grout,

as manufactured by Quikrete, and trowelled to a flat surface. The installed

HPFRCC link slab is shown in Figure 3-15.

Figure 3-15: Installed HPFRCC Link Slab

33

4 Analysis

4.1 Specimen #1

The loads applied to specimen #1 using the hydraulic actuator is reported in

Figure 4-1. The actuator displacement was plotted against the number of

cycles because the actuator displacement remains consistent throughout

cycling at the target strains. The specimen was loaded and cycled at the

strains 0.5%, 0.6%, 0.85%, and then loaded till failure. These target strains

represent the gap displacement relative to the unbonded length, which is the

physical displacement of the composite deck.

Figure 4-1: Specimen #1 Actuator Load vs Cycles

(A) Load to 0.5% Tensile Strain

(B) First cycle at 0.5% Tensile Strain

(C) Cycle at 0.5% Tensile Strain

(D) Load to 0.6% Tensile Strain

(E) Cycle at 0.6% Tensile Strain

(F) Load to 0.85% Tensile Strain

(G) Cycle at .85% Tensile Strain

(H) Max Compression and Load to Failure

34

Figure 4-2 is the plots of Actuator Load versus Actuator Displacement of

Specimen #1, which correlate directly to the stress and strain in the

composite deck. After initial onset of loading to a target strain, the composite

deck approached more elastic behavior as more cycles were applied and the

material was developing micro cracks. This can be seen in the plot when

loading to 0.5% strain, the actuator must apply increased load to achieve a

relatively small displacement gain. As the load is cycled at the 0.5% strain, it

takes less force to get the same displacement when loading. The same

occurs when loading and cycling at any other strain. Also, the stress versus

strain load paths during the compression and tension loading cycle tended to

approach a single load path after each subsequent cycle.

Figure 4-2: Specimen #1 Actuator Load vs Displacement

‐30

‐20

‐10

0

10

20

30

40

‐2.5‐2‐1.5‐1‐0.500.5

Actuator Load

(kips)

Actuator Displacement (in)

Specimen #1 ‐ Actuator Load vs Displacement (Load to 0.5% Tensile Strain)

‐30

‐20

‐10

0

10

20

30

40

‐2‐1.5‐1‐0.500.51

Actuator Load

(kips)


Specimen #1 ‐ Actuator Load vs Displacement ( First Cycle at 0.5% Tensile Strain)

‐30

‐20

‐10

0

10

20

30

40

‐2‐1.5‐1‐0.500.51

Actuator Load

(kips)


Specimen #1 ‐ Actuator Load vs Displacement (Cycle at 0.5% Tensile Strain)

‐30

‐20

‐10

0

10

20

30

40

‐3‐2.5‐2‐1.5‐1‐0.500.51

Actuator Load

(kips)



35

Figure 4-2(cont.): Specimen #1 Actuator Load vs Displacement

The unbonded section stress versus unbonded strain is plotted in Figure 4-3.

The link slab change in length measured from the unbonded to unbonded

section is linearly related to the physical gap of the frame structure. That is,

the unbonded section stress versus strain plot is expected to mimic the

Actuator Load versus Displacement plot. Similar observations can be seen

as described in the Actuator Load versus Displacement plot. As can be seen

in the unbonded stress versus strain plots, although the link slab was able to

‐30

‐20

‐10

0

10

20

30

40

‐3‐2.5‐2‐1.5‐1‐0.500.51

Actuator Load

(kips)



‐40

‐30

‐20

‐10

0

10

20

30

40

50

‐4‐3‐2‐1012

Actuator Load

(kips)



‐40

‐30

‐20

‐10

0

10

20

30

40

‐4‐3‐2‐1012

Actuator Load

(kips)



‐8

‐6

‐4

‐2

0

2

4

6

8

‐0.6‐0.4‐0.200.20.40.6

Actuator Load

(kips)


Specimen #1 ‐ Actuator Load vs Displacement (Max Compression)

0

5

10

15

20

25

30

35

40

45

50

‐7‐6‐5‐4‐3‐2‐10

Actuator Load

(kips)


Specimen #1 ‐ Actuator Load vs Displacement (Load to Failure)

36

reach a tensile strain greater than 1.0%, the max compressive strain was

less than 0.08%.

Figure 4-3: Specimen #1 Unbonded Section Stress vs Strain

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Unbonded Section Stress vs Strain(Load to 0.5% Tensile Strain)

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Unbonded Section Stress vs Strain(First Cycle at 0.5% Tensile Strain)

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Unbonded Section Stress vs Strain(Cycle at 0.5% Tensile Strain)

‐0.5

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007

Stress (Ksi)

Strain (in/in)


‐0.5

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007

Stress (Ksi)

Strain (in/in)


‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 0 0.002 0.004 0.006 0.008 0.01

Stress (Ksi)

Strain (in/in)


37

Figure 4-3(cont.): Specimen #1 Unbonded Section Stress vs Strain

The Bonded Section Stress versus Strain for Specimen #1 is plotted in

Figure 4-4. Like the Unbonded plot, the Bonded section Stress versus Strain

plot mimics the Actuator Load versus Displacement Plot. Similarly, the same

observations can be made.

Figure 4-4: Specimen #1 Bonded Section Stress vs Strain

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 0 0.002 0.004 0.006 0.008 0.01

Stress (Ksi)

Strain (in/in)


‐0.1

‐0.08

‐0.06

‐0.04

‐0.02

0

0.02

0.04

0.06

0.08

0.1

‐0.0006‐0.0004‐0.0002 0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Unbonded Section Stress vs Strain(Max Compression)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Unbonded Section Stress vs Strain(Load to Failure)

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Bonded Section Stress vs Strain(Load to 0.5% Tensile Strain)

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.001 0 0.001 0.002 0.003 0.004

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Bonded Section Stress vs Strain(First Cycle at 0.5% Tensile Strain)

38

Figure 4-4(cont.): Specimen #1 Bonded Section Stress vs Strain

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Bonded Section Stress vs Strain(Cycle at 0.5% Tensile Strain)

‐0.5

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006

Stress (Ksi)

Strain (in/in)


‐0.5

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006

Stress (Ksi)

Strain (in/in)


‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 0 0.002 0.004 0.006 0.008

Stress (Ksi)

Strain (in/in)


‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 0 0.002 0.004 0.006 0.008

Stress (Ksi)

Strain (in/in)


‐0.1

‐0.08

‐0.06

‐0.04

‐0.02

0

0.02

0.04

0.06

0.08

0.1

‐0.0006 ‐0.0004 ‐0.0002 0 0.0002 0.0004 0.0006 0.0008 0.001

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Bonded Section Stress vs Strain(Max Compression)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.002 0.004 0.006 0.008 0.01

Stress (Ksi)

Strain (in/in)

Specimen #1 ‐ Bonded Section Stress vs Strain(Load to Failure)

39

The unbonded section elongation versus Gap displacement is plotted in

Figure 4-5. For the cycling at strains 0.5% and 0.6% tensile strain, the

unbonded elongation and gap displacement are linearly correlated at a near

1:1 ratio. As the specimen is cycled at increased strains of 0.85% or until

failure, the correlations remains linear but gap displacement opens more

than the unbonded section elongates.

Figure 4-5: Specimen #1 Unbonded Section vs Gap

‐0.1

‐0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

‐0.1 0 0.1 0.2 0.3 0.4

Unbonded Section Displacement (in)

Gap Displacement (in)

Specimen #1 ‐ Unbonded Section vs Gap Displacement (Cycle at 0.5% Tensile Strain)

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6Unbonded Section Displacement (in)



‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7




‐0.04

‐0.02

0

0.02

0.04

0.06

0.08

‐0.06 ‐0.04 ‐0.02 0 0.02 0.04 0.06 0.08 0.1



Specimen #1 ‐ Unbonded Section vs Gap Displacement (Max Compression)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1



Specimen #1 ‐ Unbonded Section vs Gap Displacement (Load to Failure)

40

The bonded section displacement versus gap displacement is plotted in

Figure 4-6. Similar to the unbonded section, the bonded section elongation is

correlated linearly to the gap displacement, however, this remains near a 1:1

ratio throughout through all cycled strains including failure.

Figure 4-6: Specimen #1 Bonded Section vs Gap Displacement

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.1 0 0.1 0.2 0.3 0.4

HPFR

CC Bonded Section (in)


Specimen #1 ‐ Bonded Section vs Gap Displacement (Cycle to 0.5% Tensile Strain)

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6

HPFR



Specimen #1 ‐ Bonded Section vs Gap Displacement (Cycle to 0.6% Tensile Strain)

‐0.2

0

0.2

0.4

0.6

0.8

‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

HPFR



Specimen #1 ‐ Bonded Section vs Gap Displacement (Cycle to 0.85% Tensile

Strain)

‐0.06

‐0.04

‐0.02

0

0.02

0.04

0.06

0.08

0.1

‐0.06 ‐0.04 ‐0.02 0 0.02 0.04 0.06 0.08 0.1

HPFR



Specimen #1 ‐ Bonded Section vs Gap Displacement (Max Compression)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

HPFR



Specimen #1 ‐ Bonded Section vs Gap Displacement (Load to Failure)

41

4.2 Specimen #2

Note: Specimen #2 was tested in a similar manner to Specimen #1. Much of

the same verbiage is repeated for convenience.





strains 0.55%, 0.8%, and then loaded till failure. These target strains





(B) Cycle at 0.55% Tensile Strain

(C) Load to 0.8% Tensile Strain

(D) Cycle at 0.8% Tensile Strain

(E) Load to Failure

42







relatively small displacement gain. As the load is cycled at the 0.55% strain,

it takes less force to get the same displacement when loading. The same





‐10

‐5

0

5

10

15

20

‐2.5‐2‐1.5‐1‐0.500.5

Actuator Load

(Kips)



‐15

‐10

‐5

0

5

10

15

20

‐2.5‐2‐1.5‐1‐0.500.5

Actuator Load

(Kips)



‐20

‐15

‐10

‐5

0

5

10

15

20

‐4‐3‐2‐101

Actuator Load

(Kips)



‐20

‐15

‐10

‐5

0

5

10

15

20

‐3.5‐3‐2.5‐2‐1.5‐1‐0.500.51

Acturator Load

(Kips)



43

Figure 4-8(cont.): Specimen #2 Actuator Load vs Displacement

The unbonded section stress versus unbonded strain is plotted in Figure 4-9.

The link slab change in length measured from the unbonded to unbonded




as described in the Actuator Load versus Displacement plot. However, the

unbonded section only reached a strain of about 0.5% before failure.


‐20

‐15

‐10

‐5

0

5

10

15

20

‐4‐3‐2‐1012

Actuator Load

(Kips)



‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #2 ‐ Unbonded Section Stress vs Strain (Load to 0.55% Tensile Strain)

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #2 ‐ Unbonded Section Stress vs Strain (Cycle at 0.55% Tensile Strain)

44

Figure 4-9(cont.): Specimen #2 Unbonded Section Stress vs Strain


Figure 4-10. Like the Unbonded plot, the Bonded section Stress versus

Strain plot mimics the Actuator Load versus Displacement Plot. Similarly, the

same observations can be made.

Figure 4-10: Specimen #2 Bonded Section Stress vs Strain: Load to Failure

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007

Stress (Ksi)

Strain (in/in)

Specimen #2 ‐ Unbonded Section Stress vs Strain (Load to 0.8% Tensile Strain)

‐0.5

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007

Stress (Ksi)

Strain (in/in)

Specimen #2 ‐ Unbonded Section Stress vs Strain (Cycle at 0.8% Tensile Strain)

‐0.5

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.003 ‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006

Stress (Ksi)

Strain (in/in)

Specimen #2 ‐ Unbonded Section Stress vs Strain (Load to Failure)

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #2 ‐ Bonded Section Stress vs Strain (Load to 0.55% Tensile Strain)

‐0.4

‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #2 ‐ Bonded Section Stress vs Strain (Cycle at 0.55% Tensile Strain)

45

Figure 4-10(cont.): Specimen #2 Bonded Section Stress vs Strain: Load to Failure


Figure 4-11. As the specimen is cycled, the correlation between the

unbonded elongation and the gap displacement remains relatively linear,

however, the gap displacement opens more than the unbonded section

elongates.

Figure 4-11: Specimen #2 Unbonded Section Displacement vs Gap

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006

Stress (Ksi)

Strain (in/in)


‐0.5‐0.4‐0.3‐0.2‐0.1

00.10.20.30.40.50.6

‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006

Stress (Ksi)

Strain (in/in)

Specimen #2 ‐ Bonded Section Stress vs Strain (Cycle at 0.8% Tensile Strain)

‐0.5‐0.4‐0.3

‐0.2‐0.1

00.1

0.20.30.4

0.50.6

‐0.003 ‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #2 ‐ Bonded Section Stress vs Strain (Load to Failure)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 0.1 0.2 0.3 0.4 0.5

Unbonded Section (in)


Specimen #2 ‐ Unbonded Section vs Gap Displacement (Load to 0.55% Tensile Strain)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 0.1 0.2 0.3 0.4 0.5




46

Figure 4-11(cont.): Specimen #2 Unbonded Section Displacement vs Gap


Figure 4-12. Similar to the unbonded section, the bonded section elongation

is correlated linearly to the gap displacement, however, this remains near a

1:1 ratio throughout through all cycled strains including failure.

Figure 4-12: Specimen #2 Bonded Section Displacement vs Gap: Load to Failure

‐0.050

0.050.10.150.20.250.30.350.40.450.5

‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6




‐0.050

0.050.10.150.20.250.30.350.40.450.5

‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6




‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

‐0.3 ‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6




0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 0.1 0.2 0.3 0.4 0.5

HPFR

CC Bonded Section

Displacement (in)


Specimen #2 ‐ Bonded Section vs Gap Displacement (Load to 0.55% Tensile Strain)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 0.1 0.2 0.3 0.4 0.5

HPFR

CC Bonded Section

Displacement (in)


Specimen #2 ‐ Bonded Section vs Gap Displacement (Cycle at 0.55% Tensile Strain)

47

Figure 4-12(cont.): Specimen #2 Bonded Section Displacement vs Gap: Load to Failure

4.3 Specimen #3

Note: Specimen #3 was tested in a similar manner to Specimen #1 and #2.

Much of the same verbiage is repeated for convenience.





strains 0.55%, 0.85%, and then loaded till failure. These target strains



‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6

HPFR

CC Bonded Section

Displacement (in)



‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6

HPFR

CC Bonded Section

Displacement (in)



‐0.3

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.3 ‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5

HPFR

CC Bonded Section

Displacement (in)



48



(B) Cycle at 0.55% Tensile Strain

(C) Load to 0.85% Tensile Strain

(D) Cycle at 0.85% Tensile Strain

(E) Load to Failure







relatively small displacement gain. As the load is cycled at the 0.55% strain,

it takes less force to get the same displacement when loading. The same




49


The unbonded section stress versus unbonded strain is plotted in Figure 4-

15. The link slab change in length measured from the unbonded to unbonded




as described in the Actuator Load versus Displacement plot. However, the

unbonded section only reached a strain of about 0.45% before failure.

‐30

‐25

‐20

‐15

‐10

‐5

0

5

10

15

20

‐2.5‐2‐1.5‐1‐0.500.511.5

Actuator Load

(Kips)



‐30

‐25

‐20

‐15

‐10

‐5

0

5

10

15

‐2.5‐2‐1.5‐1‐0.500.511.5

Actuator Load

(Kips)



‐40

‐30

‐20

‐10

0

10

20

‐4‐3‐2‐1012

Actuator Load

(Kips)



‐35

‐30

‐25

‐20

‐15

‐10

‐5

0

5

10

15

‐4‐3‐2‐1012

Actuator Load

(Kips)



‐30

‐25

‐20

‐15

‐10

‐5

0

5

10

15

20

‐5‐4‐3‐2‐1012

Actuator Load

(Kips)



50



Figure 4-16. Like the Unbonded plot, the Bonded section Stress versus

Strain plot mimics the Actuator Load versus Displacement Plot. Similarly, the

same observations can be made.

‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #3 ‐ Unbonded Stress vs Strain (Load to 0.55% Tensile Strain)

‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #3 ‐ Unbonded Stress vs Strain (Cycle at 0.55% Tensile Strain)

‐1.2

‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006

Stress (Ksi)

Strain (in/in)

Specimen #3 ‐ Unbonded Stress vs Strain (Load to 0.85% Tensile Strain)

‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #3 ‐ Unbonded Stress vs Strain (Cycle at 0.85% Tensile Strain)

‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #3 ‐ Unbonded Stress vs Strain (Load to Failure)

51

Figure 4-16: Specimen #3 Bonded Section Stress vs Strain


Figure 4-17. As the specimen is cycled, the correlation between the

unbonded elongation and the gap displacement is no longer linear in

comparison to Specimens #2 and #3.

‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #3 ‐ Bonded Section Stress vs Strain (Load to 0.55% Strain)

‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005

Stress (Ksi)

Strain (in/in)

Specimen #3 ‐ Bonded Section Stress vs Strain (Cycle at 0.55% Strain)

‐1.2

‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007

Stress (Ksi)

Strain (in/in)


‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 ‐0.001 0 0.001 0.002 0.003 0.004 0.005 0.006

Stress (Ksi)

Strain (in/in)

Specimen #3 ‐ Bonded Section Stress vs Strain (Cycle at 0.85% Strain)

‐1

‐0.8

‐0.6

‐0.4

‐0.2

0

0.2

0.4

0.6

‐0.002 0 0.002 0.004 0.006 0.008 0.01

Stress (Ksi)

Strain (in/in)

Specimen #3 ‐ Bonded Section Stress vs Strain (Load to Failure)

52

Figure 4-17: Specimen #3 Unbonded Section vs Gap


Figure 4-18. The bonded section elongation is correlated linearly to the gap

displacement, however, this remains near a 1:1 ratio only when loaded to the

0.55% tensile strain. In all subsequent cycles, the gap displacement

increased more than the elongation in the bonded section.

‐0.1

‐0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5

Unbonded Section

Displacement (in)



‐0.1

‐0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5

Unbonded Section

Displacement (in)



‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Unbonded Section

Displacement (in)



‐0.15

‐0.1

‐0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Unbonded Section

Displacement (in)



‐0.15

‐0.1

‐0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

‐0.2 0 0.2 0.4 0.6 0.8 1

Unbonded Section

Displacement (in)



53

Figure 4-18: Specimen #3 Bonded Section vs Gap

‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5

HPFR

CC Bonded Section

Displacement (in)



‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5

HPFR

CC Bonded Section

Displacement (in)



‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

HPFR

CC Bonded Section

Displacement (in)



‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

‐0.2 ‐0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

HPFR

CC Bonded Section

Displacement (in)



‐0.2

‐0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

‐0.2 0 0.2 0.4 0.6 0.8 1

HPFR

CC Bonded Section

Displacement (in)



54

55

5 Discussion

5.1 Specimen #1

One advantage of using cast-in-place HPFRCC link slab, is that it was very

well bonded to the reinforced concrete deck. In fact, majority of the micro

cracks developed exclusively within the unbonded section. Figure 5-1

illustrates the failure mechanism observed for Specimen #1. At initial loading,

majority of the cracks developed within the unbonded section. However, one

crack began to localize near the transition point between the unbonded and

bonded section. Though a uniform distribution between micro cracks

developed, about 1cm between each crack, the localized crack at the

transition point propagated to the entire cross section of the link slab and

eventually the HPFRCC failed. Once the HPFRCC failed, the entire load was

carried by the GFRP bars. However, it was observed that the GFRP bars did

not have much capacity beyond the failure of the HPFRCC and failed soon

after.

Figure 5-1: Specimen #1 Failure Diagram

56

The unbonded section elongation was about equal to the gap displacement

for tensile strains up to 0.6% as discussed in section 4.1. This tells us the link

slab is working as designed, with all the required strain being taken up by the

micro cracks within the unbonded section. However, it was also noted that

beyond that strain, the gap displacement was greater than the unbonded

section elongation. Meaning, at tensile strains greater than 0.6% either the

crack at the transition point has opened up excessively, the bonded section

has begun to undergo elongation as well, or a combination of both of these.

Localized cracks at the transition point between the unbonded and bonded

section, as well as the visual opening of the cold joint between the HPFRCC

slab and reinforced concrete show that the link slab movement and

elongation was no limited to unbonded section.

Another disadvantage of using a cast-in-place link slab is that the micro

cracks must be developed after installation. However, it was observed that it

takes more load to develop cracks in the slab than it takes to cycle at an

equivalent strain. In practical applications, service loads may or may not be

large enough to develop the micro cracks needed for the link slab to be

effective.

Though the link slab performed well under tensile loads, the disadvantage of

using a cast-in-place slab was its low compressive strain capacity. It was

observed from the plots in section 4.1, that when cycled at the same

compressive force, the link slab does not return to the same strain. This was

most obvious before and after micro cracks were developed, but was also

observed after each subsequent cycle. This is due to the polyethylene fibers

in the HPFRCC that slide out of place to develop micro cracks in tension

never fully return to their original position regardless of the compression load

applied. Theoretically, this will create a compressive force within the link slab

which would never be dissipated and essentially limit the function of the link

57

slab. To mediate this problem, precracking was used in specimens #2 and

#3. By precracking the specimens, the permanent strain in the link slab from

micro cracking is achieved before the slab is in place. This ensures, that the

link slab has already achieved some elasticity before installation.

5.2 Specimen #2

Specimen #2 was a precast HPFRCC link slab designed to have some

compressive strain capacity. This was achieved by precracking the link slab

as described in section 3.2. The advantage of precracking the link slab is that

micro cracks were developed before placing the link slab into the reinforced

concrete deck. As discussed in section 5.1, the load required to initiate micro

cracking may be higher than actual service loads. By precracking the link

slab, it ensures some elastic action even at smaller loads. Similarly, because

the micro cracks in the link slab are open when installed, they have some

capacity to close when a compressive force is applied. In Specimen #1, the

maximum compressive strain was about 0.08%. In specimen #2 with

precracking, the maximum compressive strain was increased to 0.2%. This

gain in compressive strain capacity may be adequate enough to for daily

thermal expansion or other compressive forces.

In practical applications, using a precast link slab is more suitable for retrofits

due to the long setting and curing times of HPFRCC.

However, the primary problem with using a precast link slab was the

anchoring method of the bonded section, which was the failure mechanism of

Specimen #2. Figure 5-2 illustrates the failure mechanism observed. The

bonded section in Specimen #2 was anchored using vertical dowels,

horizontal GFRP bars, and grout below the 1 foot bonded section. At the first

application of load, though some of the micro cracks opened, majority of the

movement was at the cold joint between the HPFRCC link slab and the

58

reinforced concrete deck. This tells us (1) the grout below the bonded section

was not effective, (2) the vertical steel dowels had some capacity to deflect

before they could resist load, and (3) the grout was not bonded well to the

horizontal GFRP bars. As the applied load was increased, the bonded

section began to lift up on one end and pivot about the vertical dowels, which

was due to the vertical dowels placed in a single row. Additionally, though

micro cracks opened within the unbonded section, localized cracking was

observed at the transition point between the unbonded and bonded section.

Eventually, the bonded section lifted up enough and the GFRP bars failed in

shear.


As discussed in section 4.2, the elongation of the bonded section was

greater than the elongation in the unbonded section. This confirms that much

of the cracks that developed occurred outside of the unbonded section.

Additionally, cracks were observed in the grouted horizontal GFRP bars that

59

propagated 45 degrees to the application of tensile load. This shows that the

doweled GFRP bars were resisting load.

Though Specimen #2 had a higher compressive strain capacity, the

anchoring of the link slab limited the maximum tensile strain capacity to

0.6%. It should be noted that this maximum tensile strain did not occur at the

failure of the link slab. Failure of the slab occurred during cycling at a tensile

strain capacity of 0.5% when the GFRP bars reached their shear capacity

limit.

To mediate this problem, it was proposed to dowel 2 alternating rows of

vertical anchors to keep the bonded section from lifting. Similarly, it was

noted that doweling the horizontal GFRP bars were more difficult to install

than the vertical steel dowels. Also, neither Specimen #1 or #2 showed

evidence that the horizontal GFRP bars required more than the 1 foot

bonded section to reach its full tensile capacity. These were tested in

Specimen #3.

5.3 Specimen #3

Specimen #3 was constructed similar to Specimen #2 but was only anchored

with vertical dowels and grout below the 1 foot bonded section. Because of

the lifting of the bonded section in Specimen #2, the dowels used in

Specimen #3 were placed in 2 alternating rows. However, this did not

improve the results from Specimen #2. It was found that the maximum

compressive strain and tensile strain were about 0.14% and 0.45%

respectively.

Figure 5-3 illustrates the failure mechanism of Specimen #3. At the

application of load, the cold joint between the HPFRCC link slab and the

reinforced concrete deck began to open up. As more load was applied the

60

entire link slab began to lift up and eventually slip out of the vertical dowels.

Though the vertical dowels were adequate enough to anchor the link slab

horizontally, the bond between the grout and the vertical dowels were not

adequate enough to hold the link slab in place. During cycling, the link slab

would lift during tensile loads and would not return to its original position

regardless of the compression loads.


Specimens #2 and #3 showed that precracking a link slab gave adequate

compressive strain capacity and if precracked and anchored properly can

attain higher tensile strain capacities.

61

6 Conclusions/Recommendations

A cast-in-place link slab has the advantage of providing good continuity at

the ends of the FRCC section to the concrete or bridge deck, meaning it

can be built to be flush with the bridge deck. However, because of the

limitation of permanent strain in the link slab, the effectiveness of the slab

in compression is reduced. Therefore, a precracked link slab would be

more appropriate in most applications.

Because HPFRCC concrete requires a long setting and curing time to

reach its optimal strength, it may not be practical to cast-in-place

especially when time is a construction consideration.

Precracking of the link slab though effective requires a different means of

pre cracking than used in specimens #2 and #3. In these specimens,

precracking was done by inducing an internal moment in the link slab

which induced some localized cracking. To minimize crack localization,

physical bending of the link slab may be more effective. The possibility of

sliding the link slab through a series of rollers may be a possible solution

for this.

Pre-cast slabs has the advantage of pre-cracking but are limited by the

bond of the link slab to the existing concrete. The following bonding

methods may be considered:

a. Vertical dowels can be installed at an angle so that the slab is

essentially pulled downward during tension loads.

b. A combination of vertical dowels and horizontal GFRP bars

similar to specimens #2 and #3 would be more effective than

either acting alone.

62

Because localized cracking became a problem in all 3 specimens it may

be worth considering increasing the depth of the HPFRCC link slab (i.e.

3.5" or 4")

Water or rain run-off may seep through and get trapped below the link slab

causing the unbonded section to be susceptible to deterioration and traffic

induced damage.

63

7 References

[1] Ahmed, S. F. U. and H. Mihashi. 2007. "A review on durability

properties of strain hardening fibre reinforced cementitious composites

(SHFRCC)". Cement & Concrete Composites 29 (2007): p.365-376.

[2] Caner, A. and P. Zia. 1998. "Behavior and Design of Link Slabs for

Jointless Bridge Decks". PCI Journal, May-June 1998: p.68-73.

[3] El-Safty, A. and A. M. Okeil. 2008. "Extending the service life of

bridges using continuous decks". PCI Journal, November-December

2008:p.96-111.

[4] Keoleian, G. A., Kendall, A., Dettling, J. E., Smith, V. M., Chandler, R.

F., Lepech, M. D. and V. C. Li. 2005. "Life Cycle Modeling of Concrete

Bridge Design: Comparison of Engineered Cementitious Composite

Link Slabs and Conventional Steel Expansion Joints". Journal of

Infrastructure Systems, Vol. 11, No. 1, March 1, 2005: p.51-60.

[5] Kim, D., Naaman, A. E. and S. El-Tawil. 2008. "Comparative flexural

behavior of four fiber reinforced cementitious composites". Cement &

Concrete Composites 30 (2008): p.917-928.

[6] Larson, M. B. 2005. "Bridge Decks Going Jointless". C&T Research

Record, Issue 100, August 2005: p.1-4.

[7] Lepech, M., Li, V. C. "Design and Field Demonstration of ECC Link

Slabs for Jointless Bridge Decks", University of Michigan.

[8] Li, V. C. and G. Fischer. "Reinforced ECC - An evolution from

materials to structures". Composite Structures, Session 5: p.105-122.

64

[9] Li, V. C., Wang, S. and C. Wu. 2001. "Tensile Strain-Hardening

Behavior of Polyvinyl Alcohol Engineered Cementitious Composite

(PVA-ECC)". ACI Materials Journal, V. 98, No. 6, November-

December 2001: p.483-492.

[10] Li, V. C., Fischer, G., Kim Y., Lepech, M., Qian, S., Weimann, M.,

Wang, S. 2003. "Durable Link Slabs for Jointless Bridge Decks Based

on Strain-Hardening Cementitious Composites" Research Report

submitted to Michigan Department of Transportation, University of

Michigan.

[11] Maggio, R. D., Frannchini, M., Guerrini, G., Poli, S. and C.

Migiliaresi. 1997. "Fibre-matrix Adhesion in Fibre Reinforced CAC-

MDF Composites". Cement and Concrete Composites 19 (1997):

p.139-147.

[12] Peled, A., Bentur, A. and D. Z. Yankelevsky. 1998. "The Nature of

Bonding Between Monofilament Polyethylene Yarns and Cement

Matrices". Cement and Concrete Composites 20 (1998): p.319-327.

[13] Qian, S., Lepech, M. D., Kim, Y. Y. and Li, V. C. 2009. "Introduction

of Transition Zone Design for Bridge Deck Link Slabs Using Ductile

Concrete". ACI Structural Journal, V. 106, No. 1, January-February

2009: p.96-105.

[14] Sirijaroonchai, K., El-Tawil, S. and G. Parra-Montesinos. 2010.

"Behavior of high performance fiber reinforced cement composites

under multi-axial compressive loading". Cement & Concrete

Composites 32 (2010): p.62-72.

65

[15] Younsi, A., Turcry, P., Roziere, E., Ait-Mokhtar, A. and A. Loukili.

2011. "Performance-based design and carbonation of concrete with

high fly ash content". Cement & Concrete Composites 33 (2011):

p.993-1000.

66

8 Appendix A: Test Photos

67

8.1 Specimen #1 Observation Photo's

Specimen #1

Visible micro cracks at end of bonded section at 0.5% Strain in link slab.

Well spaced micro cracks about 1cm apart at 0.5% Strain in link slab.

Some cracks begin to localize (0.5% Strain in link slab).

Cracks tend to localize at slab ends and becomes more controlled at first GFRP bar

(0.5% Strain in link slab).

Cold Joint between link slab and existing reinforced concrete opens up (0.5% Strain

in link slab).

Cracks tend to localize at slab ends and becomes more controlled at first GFRP bar

(0.5% Strain in link slab).

68

Cracking is more controlled at reinforcement (0.5% Strain in link slab).

Cracking is more prevalent at end of bonded section and slab edges (0.5%

Strain in link slab).

Localized cracking at 0.75% Strain. Crack between GFRP reinforcement (0.75% Strain).

Localized crack between GFRP reinforcement (0.75% Strain).

Localized crack at slab edge (0.75% Strain).

69

Cracking remains controlled at GFRP bars (0.75% Strain).

Micro cracks evenly distributed in the middle section of unbonded section (0.75%

Strain).

Localized cracking is more prevalent near end of unbonded section (1.0% Strain).

Localized cracking is more prevalent near end of unbonded section (1.0% Strain).

GFRP bars struggling to control localized cracking (1.0% Strain).

Localized cracking at end of bonded section (1.0% Strain).

Failure occurs at end of bonded section. GFRP bars failure in tension.

70

Failure occurs at end of bonded section.

71


Specimen #2

Micro cracks occur in 2'-0" dowelled section of GFRP bar.

Link slab cold joint begins to open up.

Localized cracking near slab end. Localized cracking near slab end.

Localized cracks during precracking open up under load.

Uplift of slab edge.

72

Slab edge uplifts and GFRP bars fail in shear at link slab cold joint.

After GFRP bars fail in shear, link slab is still able to resist little force but eventually

fails at end of unbonded section.

After GFRP bars fail in shear, link slab is still able to resist little force but eventually

fails at end of unbonded section.

Shear failure in GFRP bar at cold joint.

73


Specimen #3

Cracking from precracking visible before any load is applied

Shrinkage cracks in unreinforced grout.

Cracks from precracking open up under load.

Localized crack along middle section of link slab.

Cracks from precracking begin to localize. Link slab cold joint opens up on both sides.

74

Uplift of link slab edge. Pull out and uplift of link slab edge.

Link slab slipping out of outermost vertical dowels.

Extensive uplift of slab edge under cyclic loading.

Extensive uplift of slab edge considered point of failure. Applied load is continued

until failure of GFRP bar

Failure of GFRP bar.

75

Link slab failure. GFRP bar failed in tension.

Dowels remain well grouted to existing concrete.

76

9 Appendix B: Test Specimen Layout

77

78

79

Table 4: Measuring Device Abbreviations and Descriptions

Measuring Device Abbreviation

Description

ECC1 Measures the change in length from the extreme ends of the link slab. If different than UNB1 and UNB2, displacement is not limited to within the unbonded

section. (about 8'-0") ECC2 Same as ECC1. UNB1 Measures the change in length within the unbonded

section. If similar to GAP1 and GAP2, the link slab is effective in completely elastic. (about 6'-0")

UNB2 Same as UNB1. GAP1 Measures the true displacement of the concrete/bridge

deck. GAP2 Same as GAP1. STL1 Measures the true displacement of the steel girder.

Factored comparison with GAP1 and GAP2, determines the effectiveness of the steel studs and ensures no slip between the concrete slab and steel

girders. STL2 Same as STL1. B1T Measures the strain on the top flange of the steel

beam. Used to ensure equal loading on both girders. B2T Same as B1T. B1B Measures the strain on the bottom flange of the steel

beam. Used to ensure equal loading on both girders B2B Same as B1B.

Documents

PRECAST LINK SLABS FOR JOINTLESS BRIDGE DECKS · PRECAST LINK SLABS FOR JOINTLESS BRIDGE DECKS ... providing good continuity with the bridge deck, but had no compressive ... assistance