Beam End Repair For Prestressed Concrete Beams Final Report

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Beam End Repair for PrestressedConcrete BeamsFinal ReportSeptember 2020Sponsored byIowa Highway Research Board(IHRB Project TR-715)Iowa Department of Transportation(InTrans Project 17-598)

About the Bridge Engineering CenterThe mission of the Bridge Engineering Center (BEC) is to conduct research on bridgetechnologies to help bridge designers/owners design, build, and maintain long-lasting bridges.About the Institute for TransportationThe mission of the Institute for Transportation (InTrans) at Iowa State University is to developand implement innovative methods, materials, and technologies for improving transportationefficiency, safety, reliability, and sustainability while improving the learning environment ofstudents, faculty, and staff in transportation-related fields.Iowa State University Nondiscrimination StatementIowa State University does not discriminate on the basis of race, color, age, ethnicity, religion,national origin, pregnancy, sexual orientation, gender identity, genetic information, sex, maritalstatus, disability, or status as a US veteran. Inquiries regarding nondiscrimination policies may bedirected to the Office of Equal Opportunity, 3410 Beardshear Hall, 515 Morrill Road, Ames, Iowa50011, telephone: 515-294-7612, hotline: 515-294-1222, email: eooffice@iastate.edu.Disclaimer NoticeThe contents of this report reflect the views of the authors, who are responsible for the factsand the accuracy of the information presented herein. The opinions, findings and conclusionsexpressed in this publication are those of the authors and not necessarily those of the sponsors.The sponsors assume no liability for the contents or use of the information contained in thisdocument. This report does not constitute a standard, specification, or regulation.The sponsors do not endorse products or manufacturers. Trademarks or manufacturers’ namesappear in this report only because they are considered essential to the objective of the document.Iowa DOT StatementsFederal and state laws prohibit employment and/or public accommodation discrimination onthe basis of age, color, creed, disability, gender identity, national origin, pregnancy, race, religion,sex, sexual orientation or veteran’s status. If you believe you have been discriminated against,please contact the Iowa Civil Rights Commission at 800-457-4416 or Iowa Department ofTransportation’s affirmative action officer. If you need accommodations because of a disability toaccess the Iowa Department of Transportation’s services, contact the agency’s affirmative actionofficer at 800-262-0003.The preparation of this report was financed in part through funds provided by the IowaDepartment of Transportation through its “Second Revised Agreement for the Management ofResearch Conducted by Iowa State University for the Iowa Department of Transportation” and itsamendments.The opinions, findings, and conclusions expressed in this publication are those of the authorsand not necessarily those of the Iowa Department of Transportation.

1. Report No.2. Government Accession No.3. Recipient’s Catalog No.IHRB Project TR-7154. TitleBeam End Repair for Prestressed Concrete Beams5. Report DateSeptember 20206. Performing Organization Code7. Authors8. Performing Organization Report No.Behrouz Shafei (orcid.org/0000-0001-5677-6324), Brent Phares(orcid.org/0000-0001-5894-4774), and Weizhuo Shi (orcid.org/0000-00018193-0098)InTrans Project 17-5989. Performing Organization Name and Address10. Work Unit No. (TRAIS)Bridge Engineering CenterIowa State University2711 South Loop Drive, Suite 4700Ames, IA 50010-866411. Contract or Grant No.12. Sponsoring Organization Name and Address13. Type of Report and Period CoveredIowa Highway Research ProgramIowa Department of Transportation800 Lincoln WayAmes, IA 50010Final Report14. Sponsoring Agency Code15. Supplementary NotesVisit https://intrans.iastate.edu for color pdfs of this and other research reports.16. AbstractOne of the primary concerns of the use of precast prestressed concrete beam (PPCB) bridges is cracking and spalling of theconcrete towards the ends of the beams due to contamination from water and deicing chemicals, which results in exposure andcorrosion of the beams’ reinforcement and prestressing strands. If allowed to progress, this deterioration will compromise thecapacity of the beams, which can affect the integrity of the entire bridge and raise safety and durability concerns.To address this issue, the efficacy of ultra-high performance concrete (UHPC) and high early strength concrete (HESC) forstrengthening and repairing damaged prestressed concrete beams ends was evaluated. First, a review of current repair strategieswas conducted to determine the key qualities of effective repair methods. The use of unique materials with enhanced propertiesto perform patch repairs was ultimately selected as the repair method evaluated in this research project. Small-scale laboratorytesting was conducted to evaluate the bond strength of various potential patching materials in terms of shear stress and tensilestress. Full-scale laboratory testing was conducted to determine the properties and performance of UHPC and HESC as beampatching materials. Six artificially damaged prestressed concrete beams were tested in full-scale experiments: two withoutrepair, two repaired with UHPC, and two repaired with HESC.Observations indicated excellent patch bonding by the two materials tested in the full-scale portion of this research. Failure ofone of the unrepaired beams due to confinement failure demonstrated one consequence of the loss of concrete cover anddamage to the reinforcing steel caused by the beam-end damage. The outcome of this study is a set of recommendationsregarding the most effective repair methods and appropriate retrofit materials for rehabilitating prestressed concrete beam ends.17. Key Words18. Distribution Statementbeam end patching—bond strength—bridge girder repairs—high earlystrength concrete—prestressed concrete bridges—shear strength—shrinkagecompensating cement concrete—ultra-high performance concreteNo restrictions.19. Security Classification (of thisreport)20. Security Classification (of thispage)21. No. of Pages22. PriceUnclassified.Unclassified.72NA

BEAM END REPAIR FOR PRESTRESSEDCONCRETE BEAMSFinal ReportSeptember 2020Principal InvestigatorBehrouz Shafei, Associate ProfessorBridge Engineering Center, Iowa State UniversityCo-Principal InvestigatorBrent M. Phares, Research Associate ProfessorBridge Engineering Center, Iowa State UniversityResearch AssistantQuin RogersAuthorsBehrouz Shafei, Brent M. Phares, and Weizhuo ShiSponsored byIowa Highway Research Board andIowa Department of Transportation(IHRB Project TR-715)Preparation of this report was financed in partthrough funds provided by the Iowa Department of Transportationthrough its Research Management Agreement with theInstitute for Transportation(InTrans Project 17-598)A report fromBridge Engineering CenterIowa State University2711 South Loop Drive, Suite 4700Ames, IA 50010-8664Phone: 515-294-8103 / Fax: 515-294-0467https://intrans.iastate.edu

TABLE OF CONTENTSACKNOWLEDGEMENTS . ixEXECUTIVE SUMMARY . xiINTRODUCTION .1Background .1Research Objective and Scope .2Report Organization .2LITERATURE REVIEW .3Introduction .3Review of Corrosion in Prestressing Steel.4Current Practices .6Alternative Patching Materials .13Recommendations .14SMALL-SCALE BOND TESTING .17Introduction .17Experimental Program .21Results and Discussion .29Summary and Conclusions .33FULL-SCALE BEAM PATCHING TESTING .34Specimen Preparation .34Test Setup and Procedure.41Results and Discussion .43Summary and Conclusions .54SUMMARY AND CONCLUSIONS .55Summary .55Conclusions and Recommendations .55REFERENCES .57v

LIST OF FIGURESFigure 1.1. Severely corroded prestressed concrete girder (Minnesota) .1Figure 2.1. Reinforced shotcrete repair of a damaged beam end in Minnesota.8Figure 2.2. FRP stirrups (U-wrap) configuration.11Figure 3.1. Slump flow of self-consolidating concrete mixture .23Figure 3.2. Formwork retarder application .25Figure 3.3. Various levels of surface roughness for the substrate specimens: (a) slant shearspecimens and (b) splitting tensile specimens .26Figure 3.4. Splitting tensile strength test for characterizing bond strength .27Figure 3.5. Splitting tensile test sample specimen .27Figure 3.6. Slant shear test for characterizing bond (left); slant shear stresses (right) .28Figure 3.7. Slant shear test sample specimen .29Figure 3.8. Adhesion stress at failure for different patching materials .30Figure 3.9. Example of UHPC-NP specimen after failure.30Figure 3.10. Examples of partial substrate failure: HESC (left), SCC-C (right) .31Figure 3.11. Examples of failed slant shear specimens: HESC (left) and SCC-C (right) .32Figure 3.12. Examples of failed UHPC slant shear specimens.32Figure 4.1. BTC115 cross-section (left) and midspan reinforcement layout (right) .34Figure 4.2. Wire saw cutting in progress .35Figure 4.3. Cut beam segment marked for artificial damage .35Figure 4.4. Areas of simulated damage on beam specimens .36Figure 4.5. Cutting and chiseling (left), damaged bottom flange (center), and damaged web(right).36Figure 4.6. Artificially damaged beam specimen (1 ft damage).37Figure 4.7. Beam patching formwork (left) and wetted area to be patched (right) .39Figure 4.8. Patch mix being poured into formwork .40Figure 4.9. Patch mix flowing from weep holes .40Figure 4.10. Four-point loading laboratory test set up.41Figure 4.11. Beam instrumentation schematic .43Figure 4.12. Crack pattern of Control-1.44Figure 4.13. Control-2 failure .45Figure 4.14. Fractured stirrup on bottom flang

Six artificially damaged prestressed concrete beams were tested in full-scale experiments: two without repair, two repaired with UHPC, and two repaired with HESC. Observations indicated excellent patch bonding by the two materials tested in the full-scale portion of this research.

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