Mockup Injections of Alternative Flexible Fillers for Multistrand PT Bridge Tendons

Trey Hamilton, PhD, PE

Byron D. Spangler Professor of Civil Engineering

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Outline

Objective

Small scale component tests

Full scale mock up construction

Injection process and results

Comments and Observations

Future research

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Research Project

Research Project: Replaceable Unbonded Tendons for Post-Tensioned Bridges(FDOT Contract No. BDV31-977-15)

Project Mangers: Will Potter and Rick Vallier

Staff of Marcus H. Ansley Structures Research Center

Co-PI Dr. Jennifer Rice

Graduate Students: Rahul Bhatia, Natassia Brenkus, A. Abdullah

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Acknowledgements

DYWIDAG-Systems International USA Inc.

Freyssinet, Inc. USA

Schwager Davis, Inc.

VSL

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Objective

To assess the implications of using unbonded tendons with pliable filler with respect to constructability of the tendon.

Bare strand

Bundled monostrand

Epoxy coated strand Stacked

Wire tendon

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FDOT Design Bulletin

Issued April 30, 2014:

“The Florida Department of Transportation will be implementing the use of wax filler material in lieu of grout for corrosion protection on certain post-tensioning tendons in the near future.”

“All tendons with wax filler material will be assumed to be unbonded and must be designed and detailed to be fully replaceable.”

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Pros Cons

105˚C material

Duct blockage or bursting

Grease: oil separation

Effect of voids unknown

Material issues unknown

Unbonded

Material is formulated in plant, not on site

Does not use water

Corrosion prevention

Easier to repair than grout

Unbonded

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Internal and external tendons

Internal-

Drop-In

girders

External tendon-Segmental

box girder

Internal

Cantilever

tendons

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Alternative Filler Materials

Grease: semisolid lubricant that composed of liquid base oil, solid thickener, and additives. The liquid base oil is a long hydrocarbon chain or cyclic aliphatic compounds that are usually produced from refining of crude petroleum oil.

Microstructural Wax: petroleum waxes are produced by de-oiling of petrolatum (petroleum jelly). Petroleum waxes are mostly branched isoparaffinicor naphthenic hydrocarbons and differ from paraffin waxes, which have unbranched straight hydrocarbon chains. Due to their small and thin crystal structure, petroleum waxes are more flexible than the paraffin waxes.

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Filler Materials

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Rheology

Temperature (C)

Vis

co

sit

y (

Pa

-s)

Nontribos shear test

50 60 70 80 90 100 110 1200.01

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

100

Shear rate- 1/10sShear rate- 1/20sShear rate- 1/30sShear rate- 1/50sShear rate- 1/80s

cream

vegetable oil

tomato juice

mayonnaise

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Filler preparation

Barrel heaters Insulation blanketTransfer of filler

Stirring Measurement

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Small Scale Injection

~5’-0”

4-in. HDPE duct

55 gal. barrel heated to ~105° C

Return line from pump

Supply line to specimen

Return line

from specimen

pump

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Small Scale Specimens

HDPE only HDPE with saddles

HDPE with polycarbonate tube HDPE with PVC (Shrink wrap)

HDPE with thermocouple HDPE with polycarbonate tube

(vent)

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Findings-Prolonged Injection Sag in the HDPE duct

Pressure >100 psi

Duration > 8 minutes

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Findings-Voids

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(3) 19 (0.6”) strand tendons.

0.2 kip/strand prestressing to achieve profile.

4 ½” HDPE duct (DR=17); pressure rating=125 psi

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Duct Installation

Duct placement

Anchorage and couplers

Duct Windows

Welded

Joints

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Tendon installation

Strands tensioned with monostrand jack

Gravity deviators

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Instrumentation

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Visconorustin

jectio

n

Rate: ~50 fpm (32 gpm)

Burp: no

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Injection

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Visconorust-Results

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VZ inject

inje

ctio

n

inje

ctio

n

Rate: ~75 fpm (50 gpm)

Burp: yes (too fast)

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VZ inject-Results

inje

ctio

n

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Cirinject

inje

ctio

n

inje

ctio

n

Rate: ~60 fpm (40 gpm)

Burp: yes

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Cirinject-Results

inje

ctio

n

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Trenton 1-vacuum

inje

ctio

n

Rate: ~100 fpm (65 gpm)

Burp: no

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Trenton 1-Results

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Trenton 2 - Slow

inje

ctio

n

inje

ctio

n

Rate: ~20 fpm (13 gpm)

Burp: yes

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Trenton 2-Results

inje

ctio

n

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Temperature Variation

Time during injection (minute)

Te

mp

era

ture

(F

)

Te

mp

era

ture

(C

)

0 1 2 3 4 5 650

70

90

110

130

150

170

190

210

230

250

270

15

30

45

60

75

90

105

120

Sta

rt

End

T1T2T3T4T5T6T7

Time during injection (minute)

Te

mp

era

ture

(F

)

Te

mp

era

ture

(C

)

0 1 2 3 4 5 640

60

80

100

120

140

10

20

30

40

50

ST1ST2ST3ST4ST5ST6ST7

Internal

External

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Findings

Follow good grouting practice

Preheat equipment (hoses)

Feed wax to avoid splash (and foam) in open hopper pump

good results using target injection speed between 50 to 80 ft/min

No serious issues discovered with PT Anchorages or duct

Vacuum assist greatly simplified injection

Reversible variable speed pump allows better control of injection

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Future work

Heat transfer behavior of the injection in the tendon and compare the results with the closed form solution

Structural implication of unbonded tendon over the bonded tendon.

Fatigue behavior on full scale beam

Replaceability of unbonded tendons in full scale beam

Effect of moisture in duct prior to injection

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Thank you

http://www.dot.state.fl.us/structures/StructuresResearchCenter/

Progress%20Reports/BDV-31-977-15-task1.pdf