SAFETY AND SERVICEABILITYLongitudinal Cracks in the Websof Precast, Prestressed <strong>Concrete</strong> Girders:To Repair or not to Repair?by Steve Seguirant,<strong>Concrete</strong> Technology CorporationWith the increased use of higher strengthconcretes, deeper girders, and larger amountsof prestressing, longitudinal cracks in the websof precast, prestressed concrete bridge girdershave become more prevalent during the last twodecades. <strong>The</strong>se cracks generally appear at the endsof girders following transfer of the prestressingforce. Sometimes they become more noticeablewhen the girders are lifted from the castingbed. Nonprestressed transverse reinforcement isprovided at the ends of the girders to control thewidth of these cracks.In practice, there has been no consistentunderstanding of the impact of end-zone crackingon the strength and durability of the girders. Thus,the assessments made by bridge owners vary fromdoing nothing to total rejection of the girders.Other reactions include debonding of strandsat the girder ends, limiting prestressing levels,reducing the allowable concrete compressive stressat the time of transfer, injecting epoxy into thecracks, and coating the girder ends with sealants.<strong>The</strong>re has been no consensus among owners onthe level of tolerance allotted to these longitudinalcracks.With this in mind, National CooperativeHighway Research Project 18-14 was initiatedto establish a user’s manual for the acceptance,repair, or rejection of precast, prestressed concretegirders with longitudinal web cracks. <strong>The</strong> researchinvolved the following activities:• Structural investigation and full-scaletesting of girder specimens to study theeffect of end zone cracking and transversereinforcement details on shear andflexural strengths.• Epoxy injection to investigate its abilityto restore the tensile capacity of crackedconcrete.• Durability testing to investigate whatrepair methods and materials should beused if repair is deemed necessary.• Field inspection of bridges to check if thein-service condition of end zone crackingchanges with time.Based on the research, the following proposedcrack width limits were developed:• Cracks narrower than 0.012 in. may beleft unrepaired.• Cracks ranging in width from 0.012in. to 0.025 in. should be repaired byfilling the cracks with approved specialtycementitious materials, and coating theend 4 ft of the girder web side faces withan approved sealant.• Cracks ranging in width from 0.025 in. to0.05 in. should be filled by epoxy injectionand the end 4 ft of the girder web coatedwith a sealant.• For girder webs exhibiting crackswider than 0.05 in., the research teamrecommends that the girders be rejectedunless shown by detailed analysis thatstructural capacity and long-termdurability are sufficient.Although the report does not address the timingof repairs, state practices vary from repairingbefore shipment to repairing after girder erectionand the deck has been cast. In the latter case,the crack widths are likely to be less as a result ofprestress losses and the application of dead load.Consequently, a less intrusive and less expensiverepair procedure may be appropriate.Perhaps more importantly, the researchsuggests that transverse reinforcement detailshave been shown by experience to control endzonecracking so that repair is not needed. Moredetails about this reinforcement and the repairmaterials used in the research are given in the fullreport along with recommendations about repairprocedures._______Steve Seguirant of <strong>Concrete</strong> TechnologyCorporation, Federal Way, Wash., servedas a consultant on the project.Editor’s NoteThis article is based on NCHRP Report No.654 titled Evaluation and Repair Proceduresfor Precast/Prestressed <strong>Concrete</strong> Girders withLongitudinal Cracking in the Web, whichis available at www.trb.org/Publications/Blurbs/163575.aspx.Cracks ranging in width from 0.025 in. to 0.05 in. should be filled by epoxy injection. Photos: Mohsen Shahawy, SD Engineering Consultants Inc., Tallahassee, Fla.After injectionBefore shipment
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