REPAIR PROCEDURES & GUIDELINES
PRESTRESSED/PRECAST CONCRETE BRIDGE UNITS
Defective units or units damaged during handling or storage shall be evaluated for possible repair by the fabricator and the Iowa Department of Transportation as soon as practical (not to exceed 14 days). The fabricator shall propose repair procedures and list the brand name of patching material and submit a written request to the District Materials Engineer (DME) for approval and inclusion in the final beam inspection report. The District Materials Engineer, in consultation with the Construction and Materials Bureau, will have the final authority to accept, modify, or reject the repair procedure proposed by the fabricator.
Approved repair procedures that are standardized for reuse shall be documented in the plant-specific Quality Control Procedure Manual.
The following guidelines provide materials and procedures that may be used for repairs depending upon the extent of the defect or damage:
GUIDELINES FOR REPAIR OF AREAS WITH EXPOSED PRESTRESSING STRAND (STRUCTURAL TYPE)
Beams needing repair that have exposed prestress strands must undergo thorough inspection by District Materials personnel after removing forms, but before detensioning the strands. Before any repair work, exposed strands must be thoroughly cleaned while the beam stays under tension on the casting bed. A repair plan must be submitted for approval by the DME. The plan shall include a dimensioned diagram of the of the affected area, proposed repair material, and proposed repair procedures. The repair plan for both bonded and unbonded strands shall include:
2. Cleaning the exposed strands. Strands shall be free of rust, dust, grease, etc.. Use compressed air to remove dust and debris.
3. Using a repair material listed in IM 491.08 Appendix A or Appendix B, depending on application. Use of repair material not listed may be requested. A written request shall be submitted to and approved by the DME prior to beginning repairs.
4. Using repair material application procedures per manufacturer’s recommendations and instructions. Use of repair procedures differing from the manufacturer may be requested. A written request shall be submitted to and approved by the DME prior to beginning repairs.
Repair plans that impact unbonded strands must also not reengage the strands. The DME may consult with the Bridges and Structures Bureau prior to approving such plans.
Some repairs may require approved anchoring devices as listed in Office of Materials IM 453.09.
GUIDELINES FOR REPAIR OF AREAS WITHOUT EXPOSED PRESTRESSING STRAND (NON-STRUCTURAL TYPE)
Beams needing repair that do not have exposed prestress strands may be repaired after the beam is detensioned and during the finishing process prior to shipping. These repairs are more routine in nature and generally do not require District Materials inspection prior to the fabricator developing a repair plan. The repair plan must be submitted for approval by the DME. The plan shall include a dimensioned diagram of the of the affected area, proposed repair material, and proposed repair procedures. The repair plan shall include:
1. Removing unsound concrete from the area. The repair area boundary shall be at least one-half inch deep and roughly perpendicular to the finished surface. Damage to prestress strand and reinforcement shall be avoided or addressed in the repair procedure.
2. Cleaning any exposed reinforcement. Reinforcement shall be free of rust, dust, grease, etc.. Use compressed air to remove dust and debris.
3. Using a repair material listed in IM 491.08 Appendix A or Appendix B, depending on application. Use of repair material not listed may be requested. A written request shall be submitted to and approved by the DME prior to beginning repairs.
4. Using repair material application procedures per manufacturer’s recommendations and instructions. Use of repair procedures differing from the manufacturer may be requested. A written request shall be submitted to and approved by the DME prior to beginning repairs.
Some repairs may require approved anchoring devices as listed in Office of Materials IM 453.09.
Use an approved epoxy resin as listed in Materials IM 491.19, Appendix B. Follow the manufacturer instructions for mixing and injecting the resin into the crack. The repair procedure shall include details of the location of injection ports and the proposed sequence of injecting the resin into the crack through the ports. Follow manufacturer recommendations for curing.
Strand extensions that are cut off by mistake shall be repaired or may be substituted by leaving an uncut adjacent strand. Substitute strands shall have the same length and shape and maintain the vertical symmetry of the intended strand extension pattern. Consult with the DME to determine if substitute strands may be used.
If cut off strands must be repaired, use a strand of the same diameter and an approved epoxy-bonding grout as listed in IM 491.11 Appendix A that conforms to ASTM C-881 and/or AASHTO M-235 requirements. Follow the manufacturer recommendations and guidelines for preparation and mixing ratio. Prior approval of the DME shall be required.
The following procedures shall be used:
1. Drill 6 in. deep hole approximately 1/8 inch greater in diameter than the replacement strand, next to the cut-off strand.
2. Clean the hole by washing it and blowing it dry.
4. Fill the hole with a polymer grout listed in IM 491.11 Appendix A.
5. Insert the strand.
6. Cure per manufacturer’s recommendations.
7. Bend the strand at the required length from the end of the beam. (Heating and bending of the strand is not allowed.)
Strand cutoff length on ends of beams cannot vary by more than +1/2 in. of the specified length.
All completed spall and void repair sites shall be reviewed by the DME for possible containment measures. Repair site containment is intended to reduce the opportunity for dislodged repair material to fall on occupied areas under the bridge.
Containment measures shall typically be required for repair sites with any of the following characteristics:
Repair site containment shall use a Fiber Reinforced Polymer (FRP) repair system in accordance with Materials I.M. 491.25, Appendix A. Follow the manufacturer’s recommendations and guidelines for material preparation and use. When installed strictly for repair site containment purposes, manufacturer-trained/certified installer credentials are not required.
The FRP fabric shall extend at least 12 inches beyond the perimeter of the repair. The concrete surface under the fabric shall be free from fins, sharp edges, and protrusions that will cause voids or depressions behind the FRP fabric. The surface shall also be grouted to fill any voids greater than 0.5 inches in diameter and 0.125 inches in depth. Grout shall be fully cured before beginning installation of the FRP system.