EVALUATING CHLORIDE PERMEABILITY OF A … Convention/Tinnea... · Title: Microsoft PowerPoint - Tinnea WWB Presentation PTI.ppt Author: Administrator Created Date: 6/16/2006 9:41:08

EVALUATING CHLORIDE PERMEABILITY EVALUATING CHLORIDE PERMEABILITY OF A CHEMICAL GROUT USED TO SEAL OF A CHEMICAL GROUT USED TO SEAL LEAKS IN POSTLEAKS IN POST--TENSIONING DUCTS: AN TENSIONING DUCTS: AN

ACCELERATED TEST METHODACCELERATED TEST METHOD

Presented by Jack Tinnea,Presented by Jack Tinnea,

PO Box 22349PO Box 22349Seattle, Washington 98122Seattle, Washington 98122206/328206/328--7872 7872 www.tinnea.net

2006 PTI TECHNICAL CONFERENCE-SESSION-6 EVALUATING CHLORIDE PERMEABILITY OF A CHEMICAL GROUTIN POST-TENSIONING DUCTS: AN ACCELERATED TEST METHOD

JACK TINNEA

© COPYRIGHT POST-TENSIONING INSTITUTE, ALL RIGHTS RESERVED Page 1 of 32

The Project – The Need

The old Woodrow Wilson Bridge crosses the Potomac River between Washington, D.C. and Alexandria, VirginiaThe old bridge, completed in 1961, reached its design capacity of 75,000 vehicles per day within eight years of entering serviceToday the bridge carries almost three times that initial design traffic capacity


JACK TINNEA


The Project – The Need

The new Woodrow Wilson Bridge will double the number of traffic lanes, removing one of the largest traffic bottlenecks in the country.The new bridge will have a higher clearance reducing drawbridge openings about 70%The new bridge will have the option to replace HOV lanes with mass transitTotal costs are approximately $2.5 billion


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The Project – The Neighborhood

Arlington Memorial Bridge

New Woodrow Wilson Bridge


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The Bridge – Support

Pile Cap

Arches

Roadway


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The Bridge – Support

Pile Cap

PedestalArch

Roadway

Generalized Bridge Support Elevation


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The Bridge – PT Anchorage

Pile Cap

Pedestal

Precast Segments

Restrained by PT

PT Strands

PT Loop Anchors


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The Bridge – PT Anchorage

Plan Elevation


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The Bridge – Construction

Pedestals


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PT Loop Anchor Ducts in Pile Cap


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PT Loop Anchor


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Pedestal Forms


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Ducts Exiting Pile Cap


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Pedestal reinforcementPT ducts visible within the cageLighter ducts are the loops for the first segmentDarker ducts are the loop anchors extending down into the pile cap


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The Problem – Leaks

Joints in post-tensioning ducts allowed brackish Potomac River to seep into the ductsPost-tensioning strands were not yet in place


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The Problem – Likely Site

Cold Joint Below MHW


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The Problem – Solution

The water was pumped outPlugs were set in the ducts above and below the suspected jointsThe joints were injected with an acrylic gelThe plugs were removed and the ducts were flushed with clean water, dried, and no leaks

The UnknownThe chloride permeability of the gel


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Test Method – The Basis

Based on the Post-Tensioning Institute’s (PTI) Accelerated Corrosion Test Method (ACTM)Appendix B of the PTI “Specification for Grouting of Post-Tensioned Structures”Used 1000 hours as test time limit per Florida Department of Transportation Standard Specification 938-6


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Test Method –Specimen Design

Based on PTI’s ACTMPVC tubes were filled with the same grout used on-site with post-tensioning strands in the center of the tubes3½-inches of PVC removedArtificial cracks cut at exposed area midpoint Figure 1

9"

4½"

3½"

1"

7-W irePost-tensioningStrand

Clear PVCTubing

ExposedGroutSurface(Diameter ≅ 1")

End Cap

Cut 'Crack'


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Test Method – Fabrication

Specimens After Assembly and Grouting


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Test Method – Fabrication

Cutting “cracks” in specimens using masonry saw0.012 and 0.025-in. diamond jeweler’s blades were usedProfile showing “crack”before filling with gel


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Test Method – Injecting Cracks

Sections of the PVC tube were used to form injection damsEach half of the dam was fitted with a port and tubeThe gel was injected from belowCrack after injection


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Test Method – Curing

The specimens were cast and cured 10-days in the PVC tubesAfter removing the center section of PVC, the specimens were water-cured for 5 daysThe cracks were cut and the specimens were water-cured for an additional 13 days (28 total)Prior to injecting, the cracks were thoroughly rinsed with clean water.


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Test Method – ACTM

The specimens were placed into large beakers containing a 3% NaCl solutionConnections were through a multiplexer to a potentiostat.Specimens were polarized to +200 mV relative to a SCE reference electrodeSpecimens were considered to “pass” if they did not corrode for 1000 hours


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Final Test Cell Assembly


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Test Cells and Potentiostat


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Under Test After Removal

ExpandingGel


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When cutting the “cracks” we tried to leave a thin layer, 0.025-in, of grout surrounding the tendonIf the tendon was not well centered, steel could be exposed to gelIn that case failure was quickly apparent.


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The nominal resistivity of the cementitious grout is 10,000 ohm-cmThe resistivity of the gel was much lower, less than 150 ohm-cmIf the gel was in immediate contact with the steel tendon it effectively short-circuited the testLeaving a thin layer of grout completely encapsulating the tendon evaluated the grout’s ability to resist chloride ion penetration.


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Findings

Specimens that had a very thin layer of grout around the strands showed no signs of corrosionThis was after the 1000 hours of anodic polarization


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Conclusions

The gel itself was able to resist the flow of chloride ions to pass a 1000-hour ACTMThe acrylic gel has a pH of about 7.4 whereas the grout has a pH of about 12.3. This is a difference of 5 orders of magnitudeSuch a difference in pH with the difference in resistivity can cause a differential corrosion cellIt was recommended that the strands and the acrylic gel were not to come into contact


JACK TINNEA


Special Thanks

Tinnea & Associates extends our thanks toParsons CorporationMaryland State Highway AdministrationFederal Highway Administration

and to you,for your interest


JACK TINNEA


Documents

EVALUATING CHLORIDE PERMEABILITY OF A … Convention/Tinnea... · Title: Microsoft PowerPoint - Tinnea WWB Presentation PTI.ppt Author: Administrator Created Date: 6/16/2006 9:41:08