|FHWA > Engineering > Pavements > Concrete > FHWA-IF-07-034 > Appendix A|
Construction of the Iowa Highway 60 Precast Prestressed Concrete Pavement Bridge Approach Slab Demonstration Project
APPENDIX A: Project Plans From the Iowa Department of Transportation
Design for Precast Reinforced Concrete Approach Panels
Approach Panel Notes
This provision shall cover the fabrication, installation, post-tensioning, and grouting of precast prestressed concrete panels for a bridge approach slab. The term "slab" shall refer to a post-tensioned section of precast panels between the bridge abutment and the expansion joint.
Materials: materials shall conform to the requirements of the standard specifications noted herein, with the exceptions noted in these notes.
Precast panel fabrication:
Tolerances for precast panels, regardless of type shall be as shown below:
Concrete mix: the concrete mix used will be required to reach a compressive strength of 5,000 psi at 28 days as per Article 2407.03 of the standard specifications. The coarse aggregate used will have a minimum of Class 3 durability, as per Article 4115.04 of the standard specifications. The mix will be workable enough to achieve the required surface finish as described below. The contracting authority must approve the coarse aggregate to be used by the precast fabricator prior to fabrication to ensure compatibility with grinding equipment.
Non-prestressed reinforcement: all non-prestressed reinforcement, including tie bars, shall be grade 60 epoxy-coated reinforcement, conforming to the requirements of Article 4151.03 of the standard specifications. Precasting: precasting materials and procedures shall conform to Section 2407 of the standard specifications.
Post-tensioning materials: post-tensioning ducts shall be rigid galvanized corrugated metal or rigid corrugated polypropylene. The ducts shall have an inside diameter a minimum of 3/8 inch larger than the nominal diameter of the post-tensioning strand.
Grout ports shall be located in the panels as shown on the plans. The grout ports shall have a minimum 1/2 inch inside diameter and shall be compatible with the post-tensioning ducts, providing a water-tight seal between the duct and port. Grout ports shall not protrude from the finished surface of the panels.
Lifting anchors: lifting anchors shall be approved by the engineer prior to use. Lifting anchors shall be located as shown in the plans. The top of the lifting anchors shall be recessed 1/2 inch minimum from the surface of the panel.
Dowels for the expansion joints shall be grade 60 epoxy-coated dowels conforming to the requirements of Article 4151.02. The entire length of the dowel shall be coated with graphite grease or other approved bond breaker. Dowels shall remain parallel to the bottom surface of the panel.
Unless otherwise shown on the plans, the minimum length of dowel embedment on either side of the expansion joint shall be one-half the length of the dowel minus the specified initial width of the expansion joint.
Dowel expansion caps specified in the plans shall be approved by the engineer prior to use.
Finishing and texturing: unless otherwise directed by the engineer, the top surface of the panels (driving surface) shall receive a artificial turf or carpet drag texture conforming to the requirements of Section 2301.16 of the standard specifications. The texture shall be applied in a timely manner after final screeding such that the desired texture depth is achieved without disturbing the underlying concrete or turning over aggregate. The surface texture may be applied either parallel or normal to the long axis of the panel, at the discretion of the engineer.
Placement in forms: concrete formwork and placement procedures shall conform to the requirements of section 2407 of the standard specifications. Concrete shall be placed in a single lift and distributed in such a manner that embedded items such as reinforcement, ducts, dowels, anchors, and lifting devices are not dislodged by the concrete mass. Proper consolidation must be achieved such that honeycombing or segregation of the concrete does not occur and all spaces around embedded items and around the panel forms are filled.
Curing: curing of the precast panels shall conform to the requirements of Article 2407.09 of the standard specifications, with the exceptions noted below. The precast fabricator shall submit the proposed curing methods and procedures to the engineer for approval prior to placing concrete. Curing shall commence immediately after the surface finishing operation and as soon as marring of the concrete will not occur. Liquid curing compound may be applied in accordance with Article 2301.19 and section 4105 of the standard specifications to the top surface of the precast panels while in the forms at the discretion of the engineer. A minimum two applications of the curing compound, applied immediately after surface texture finishing, shall be required for liquid curing. Curing compound residue shall be removed from all adjoining surfaces prior to shipment of the panels to the jobsite.
Curing shall be maintained for a minimum of 72 hours from the beginning of curing operations on the sides and top surface of the panels. While in the forms, the forms will be considered to provide adequate curing for the edges (vertical faces) of the panels. If any part of the form is removed, the exposed surface shall be covered in accordance with Article 2407.09 of the standard specifications. Removal of panels from the forms to a storage area shall be done in such a manner that curing is not interrupted for more than four hours for any member. After removal from the forms, the panels may be cured using wet burlap mats conforming to section 4104 of the standard specifications until the end of the 72 hour curing period.
Form removal and storage: panels shall be removed from the forms in such a manner that no damage occurs to the panel. Form removal shall conform to the requirements of Article 2407.10 of the standard specifications. Any materials forming blockouts in the panels shall be removed such that damage does not occur to the panel or the blockout. Panels shall be stored in such a manner that adequate support is provided to prevent cracking or creep-induced deformation (sagging). Supports beneath the panels shall be located at approximately the same location as the lifting anchors. Panels with a uniform thickness may be stacked no higher than five panels per stack, with adequate support between panels. Panels shall be stacked such that individual panels or stacks of panels are not touching one another. Panels stored for long periods of time (longer than one month) shall be checked at least once per month to ensure creep-induced deformation does not occur.
Unobstructed ducts and conduit: after removal from the forms and prior to shipment, the precast fabricator shall check for obstructions in all post-tensioning ducts. The post-tensioning ducts shall be checked by feeding a post-tensioning strand of the same size as that specified for actual post-tensioning completely through each duct. If the strand does not slide freely through the duct, the cause of the obstruction shall be remedied, at the expense of the contractor, before the panel is shipped.
Lifting and handling: panels shall be handled in such a manner as not to damage the panel during lifting or moving. Lifting anchors cast into the panels shall be used for lifting and moving the panels at the fabrication plant. The angle between the top surface of the panel and the lifting line shall not be less than sixty degrees, when measured from the top surface of the panel to the lifting line. Damage caused to any panel, shall be repaired at the expense of the contractor to the satisfaction of the engineer.
Transportation: panels shall be transported in such a manner that the panel will not be damaged during transportation. Panels shall be properly supported during transportation such that cracking or deformation (sagging) does not occur. If more than one panel is transported per vehicle, proper support and separation must be provided between the individual panels. Panels shall be lying horizontally during transportation, unless otherwise approved.
Repairs: repairs of damage caused to the panels during fabrication, lifting and handling, or transportation shall be addressed on a case-by-case basis. Damage within acceptable limits caused to the top surface (driving surface) or to keyed edges of the panels shall be repaired using an approved repair method at the fabrication plant at the expense of the contractor. Repetitive damage to panels shall be cause for stoppage of fabrication operations until the cause of the damage can be remedied.
Demonstration of panel fit: the precast fabricator shall initially fabricate one full set of four panels and assemble these panels at the fabrication plant to demonstrate the fit of the panels to the satisfaction of the engineer. The panels shall be assembled over a level surface that will not cause damage to the panels during or after assembly. Post-tensioning shall not be required for this trial assembly, and epoxy shall not be required in the joints between panels. Joints between panels should not be more than 1/4 inch wide when assembled. Any problems with fitting the panels caused by imperfections in the panels shall be corrected prior to proceeding with panel fabrication. Panel fabrication may commence following the trial assembly only upon approval from the engineer.
Instrumentation: the precast fabricator shall permit the installation of instrumentation in the panel forms prior to placement of concrete. A schematic layout and instrumentation plan shall be provided to the fabricator and the engineer for approval prior to beginning panel fabrication. The precast fabricator shall provide at least 7 days advanced notice to the instrumentation installer before casting the instrumented panels. Instrumentation shall include, but is not limited to, temperature sensors, strain gages, and load cells.
Instrumentation shall not compromise the integrity of the reinforcing steel, pre-stressing system, or the precast panel itself. The precast fabricator shall protect the integrity of the instrumentation, including lead wires and connectors at the surface and edges of the precast panels, during fabrication and handling of the instrumented panels.
Base preparation: the precast panels shall be placed over a prepared surface as shown in the plans. The surface shall be free from debris and other materials that prevent the panels from fully resting on the base.
Grade control for placement: grade control will be established for placement of the base material to ensure long-wavelength roughness is not built into the base. Grade control will be established using stringlines, laser guidance, or other comparable methods. Grade control methods must be approved by the engineer prior to base preparation.
Panel installation on site:
Equipment: the contractor shall have all equipment required for panel installation, post-tensioning, and grouting on-site prior to beginning panel installation. Lifting and transporting equipment shall not damage the prepared base material prior to or during panel installation. Any damage to the prepared base material will be repaired at the contractor’s expense to the satisfaction of the engineer.
Friction reducing membrane: a single layer of drainable engineered fabric with frictional properties similar to polyethylene sheeting will be placed over the prepared base material, beneath the precast panels, to serve as a friction reducing membrane. The fabric shall have material properties conforming to Section 4196.01b of the standard specifications, unless otherwise approved by the engineer. Provision shall be made to prevent folds and creases in the fabric beneath the panels. The surface of the prepared base shall be free from loose debris, which may puncture the fabric prior to placement of the fabric. Any tears or punctures in the fabric shall be repaired to the satisfaction of the engineer prior to placement of the precast panels over the fabric. Provision shall be made to prevent the fabric from becoming pinched in the joints between individual precast panels during panel installation.
Temporary post-tensioning: panels shall be temporarily post-tensioned together during placement to ensure closure of transverse joints prior to final post-tensioning. Unless otherwise specified, temporary post-tensioning shall be completed after placement of no more than two adjacent panels. A minimum of two temporary post-tensioning strands shall be required for each set of precast panels. Strand used for temporary post-tensioning shall be either 1/2 inch or 0.6 inch nominal diameter, with corresponding temporary anchorage. Any damage to the precast panels during temporary post-tensioning shall be repaired at the contractor’s expense to the satisfaction of the engineer prior to installation of additional panels. No more than two panels may be placed in sequence between temporary post-tensioning operations.
Joint treatment: epoxy shall be applied to the adjoining surfaces of the precast panels prior to assembly. The epoxy material shall be suitable for bonding hardened concrete to hardened concrete and shall be approved by the engineer prior to use. Epoxy shall be proportioned and applied according to the manufacturer’s recommendations. Epoxy shall be applied to both faces of adjoining panels, and shall be kept a minimum of 1/2 inch away from duct openings. The set time of the epoxy shall be such that final post-tensioning is completed before the epoxy hardens. Excess epoxy squeezed out of the joint onto the driving surface of the precast pavement during assembly and/or post-tensioning shall be removed before it hardens. A compressible foam or neoprene gasket shall be placed around the opening of each post-tensioning duct as shown in the plans. The seal shall be continuous around each duct opening and shall be compressible such that it will not protrude from the gasket recess shown in the plans when compressed. The seal shall not cover any part of the opening to the duct and shall not inhibit the flow of grout. Provision shall be made to prevent damage to the gaskets during panel installation.
Placement technique: panels shall be installed one at a time, and shall be installed in such a manner that neither the base material nor the underlying fabric is damaged during installation. The angle between the top surface of the panel and the lifting line attached to each lifting anchor shall not be less than sixty degrees, when measured from the horizontal surface of the panel to the lifting line. Panels shall be aligned in the longitudinal direction (parallel to the roadway centerline) using the centerline of the panels. The centerline of each panel shall be marked on the top surface of the panel at the adjoining edges. The location of the centerline on each panel shall be determined from the location of the post-tensioning duct openings at the adjoining edges of the panels.
Panels may be pulled together during placement using approved temporary devices. Any damage to the panels caused by temporary devices shall be repaired at the contractor’s expense to the satisfaction of the engineer. The centerline of the panels shall be aligned to a line laid out by a surveyor (provided by the contractor) on the surface of the base prior to placement of the panels. Shims may be placed in the joints between panels to correct horizontal misalignment of the centerline of the panels. The total thickness of shims used in any joint shall be no more than 1/8 inch. Any damage caused to the panels by shims shall be repaired at the contractor’s expense to the satisfaction of the engineer.
Placement tolerances: the centerline of the panels shall be within 1/4 inch of the pre-surveyed centerline marked on the surface of the base, and the centerline of adjoining panels shall be within 1/8 inch of each other at the adjoining edges. Vertical alignment of the panels shall be such that the top surface of an individual panel is no more than 3/16 inch higher or lower than the top surface of an adjoining panel at any point along the joint between the panels. The width of the gap between adjoining panels at the top surface of the joint shall be no more than 1/8 inch after completion of temporary post-tensioning.
Patching and repairs: anchor access pockets (panel 1A and 1B) shall be patched only after completion of final stressing but prior to grouting the post-tensioning tendons. The pockets shall be patched with an approved cementitious patching material with a maximum aggregate size of at least 3/8 inch, but no greater than 1 inch. A fast-setting patching material, conforming to the requirements of Article 2529.02b of the standard specifications, shall be permitted with the approval of the engineer. The patching material shall be finished flush with the surface of the surrounding concrete and given a texture similar to the surrounding concrete. Damage caused to the precast panels during any part of the panel installation process shall be repaired by the contractor at the contractor’s expense to the satisfaction of the engineer. Repairs of damaged areas will be addressed on a case-by-case basis by the engineer. Damage within acceptable limits caused to the top surface (driving surface) or to keyed edges of the panels shall be repaired using approved repair methods and materials. Repetitive damage to panels shall be cause for stoppage of installation operations until the cause of the damage can be remedied. Patching lifting anchor recesses, abutment anchor sleeves, and damaged areas shall be completed using approved patching materials and methods.
Voids beneath pavement: the pavement shall be inspected during panel installation for voids beneath the precast panels. At the discretion of the engineer, the contractor shall be required to stop panel installation and correct imperfections in the base material causing voids beneath the precast panels.
Tying to existing pavement/bridge abutment: the precast panels shall be tied into the bridge abutment and existing pavement as shown on the plans. The top surface of the precast pavement shall be no more than 1/4 inch above or below the surface of the precast pavement and bridge deck. Diamond grinding shall be used to bring the top surface of the existing pavement and precast pavement into tolerance if necessary. Tie bars used to tie the precast panels to adjacent pavement shall be grade 60 conforming to the requirements of Article 4151.02 of the standard specifications.
Abutment anchors: the abutment anchor sleeves shall be patched prior to final stressing of the bridge approach slab panels.
Instrumentation: the contractor shall permit access to instrumentation in the precast panels during the panel installation process and shall permit instrumentation of the precast panels and post-tensioning system during the construction process. A schematic layout and an instrumentation plan shall be provided to the engineer and contractor for approval at least two weeks prior to commencement of panel installation on site. Instrumentation shall include, but is not limited to, temperature sensors, strain gages, and load cells. Instrumentation shall not compromise the integrity of the base material, pavement, or the post-tensioning system. The contractor shall protect the integrity of the instrumentation, including lead wires and connectors extending from the surface of the precast panels, during the panel installation and post-tensioning process.
Post-tensioning: post-tensioning materials, equipment, and procedures must be approved by the engineer prior to construction, as per Article 2407.11 of the standard specifications. The contractor shall use the post-tensioning system shown in the plans, unless a comparable system is submitted to the engineer and approved for use. The dimensions of the anchor access pockets may be adjusted as needed prior to fabrication of the panels. The pocket dimensions shall be such that construction traffic can pass over the pockets without damage to the vehicle or disruption to the driver. Dimensions other than those shown in the plans shall be approved by the engineer prior to fabrication of the panels.
Materials: low-relaxation, grade 270 strands with 0.6 inch nominal diameter conforming to Article 4151.05 of the standard specifications, shall be used for longitudinal and transverse post-tensioning of the adjoining approach pavement.
Tendon installation: longitudinal post-tensioning strands shall be inserted into the ducts as shown on the plans. Strands shall be either pushed or pulled through the ducts by hand or using an approved mechanical strand pusher. Provision shall be made to prevent separation of the individual wires from the strand during strand insertion. Transverse post-tensioning strands shall be installed but not stressed prior to stressing of the longitudinal tendons.
Post-tensioning tendons shall be stressed to 75 percent of the guaranteed ultimate tensile strength of the strand supplied. Stressing shall be completed in a single stage unless otherwise specified. Stressing of longitudinal tendons (parallel to the roadway centerline) shall start with the tendon at or near the midpoint of the panels, subsequently alternating between the tendons on either side of the centerline until all tendons have been stressed. Tendon elongations shall be measured and recorded, in accordance with Article 2407.06 of the standard specifications. Stressing of the transverse tendons shall be completed only after final stressing of the longitudinal tendons is complete. After completion of post-tensioning, the tails of the post-tensioning strands shall be trimmed, and an approved grease cap will be used to cover and seal the end of the strand and post-tensioning anchor.
Faulty anchors and wire failures: in the event of a faulty post-tensioning anchor, the contractor shall submit a repair or alternate stressing strategy for approval. No wire failures shall be accepted. The contractor shall provide and install a new strand in the event of a wire failure.
Tendon grouting: the post-tensioning system shall consist of grouted tendons for both the bridge approach slab.
Materials: the grout mixture shall be a pre-packaged grout specifically manufactured for prestressed tendon grouting, and shall be approved by the engineer prior to use. Grout shall be proportioned with water according to the manufacturer’s recommendations.
Equipment: grouting equipment shall consist of at least the following:
Procedures: a grouting plan shall be submitted to the engineer for approval at least four weeks before starting grouting operations. Grouting shall be completed within seven days after stressing of the post-tensioning tendons, unless otherwise approved. Grouting shall not be performed until the anchor access pockets have been patched. The sides of the pavement slab shall be sealed or backfilled to prevent grout leakage from beneath the slab if grouting is completed prior to placement of adjacent pavement. The grout fluidity shall be checked in accordance with Article 2539.03 of the standard specifications. Efflux time for fluidity shall be between 10 and 30 seconds after mixing, but no more or less than recommended by the manufacturer. Fluidity shall be adjusted to achieve the necessary flow requirements to achieve fully grouted tendons. If excessive bleeding of the grout is observed, the engineer may require the contractor to adjust the grout mixture to reduce bleed. The fluidity of the grout shall be checked at the beginning of each grouting operation and after each time the grout pump and hose is flushed. Samples for grout compressive strength determination will be collected at least once per day during grouting operations. A minimum of three strength cubes shall be made during each sampling. The average compressive strength of three cubes shall be a minimum of 5,000 psi at 28 days. Grout shall be pumped into the lowest end of each the tendon. Grouting pressure shall not exceed the bursting pressure of the duct/port connection or 145 psi, whichever is less. If grout does not flow from the nearest intermediate port or from the port at the opposite end of the tendon after the maximum grouting pressure has been reached, grout may be pumped into an intermediate port or into the other end of the tendon. A diagram of grout flow shall be produced by the contractor to demonstrate full grouting of the tendons.
Grouting problems: if grout is observed leaking into an expansion joint, from the end of a joint between panels, from beneath the slab, or out of an adjacent duct, pumping shall be stopped and grout shall be pumped into the nearest intermediate port. Any grout that flows into an expansion joint shall be flushed from the expansion joint immediately. Any grout that hardens in an expansion joint shall be removed at the contractor’s expense.
Cleanup: upon completion of grouting, recesses in the surface of the panels at the grout ports shall be filled with an approved mortar and finished flush with the surface of the pavement. Any grout that flows onto the finished surface of the pavement during the grouting operation shall be immediately flushed from the surface. Any residual grout which hardens on the pavement surface shall be removed using an approved technique to the satisfaction of the engineer at the expense of the contractor.
Underslab grouting: underslab grouting shall be used to fill any voids beneath the precast panels that may be present after placing the panels over the prepared base. Underslab grouting shall utilize the underslab grout ports cast into the panels.
Materials: grout materials shall conform to the requirements of Section 2539 of the standard specifications. All materials shall be furnished by the contractor.
Equipment: equipment for underslab grouting shall conform to the requirements of Section 2539 of standard specifications, with the exception that drilling equipment shall not be required unless directed by the engineer.
Proportioning grout mixture: the mixture used for underslab grouting shall conform to the requirements of Section 2539 of the standard specifications. The seven day compressive strength of the grout slurry shall not be less than 200 psi. The contractor shall furnish the engineer the proposed mix design meeting these requirements.
Procedures: underslab grouting procedures shall conform to the requirements of Section 2539, with the exceptions noted below. Underslab grouting shall be completed after stressing of the post-tensioning tendons, but not more than seven days after placement of the precast panels. The engineer may require grouting to be completed prior to opening the pavement to traffic if significant voids are observed during panel placement. Underslab grouting may be completed prior to tendon grouting only if underslab grouting will not interfere with tendon grouting.
Slab edges shall be backfilled or sealed to prevent grout leakage from beneath the slab if the adjacent pavement has not been placed prior to grouting. Likewise, the bottom of all expansion joints shall be sealed prior to underslab grouting to prevent grout leakage into the joints. The sealant material shall be compressible such that it will not inhibit free movement and full closure of the expansion joints.
Underslab grouting shall require minimal pressure to force the grout beneath the pavement slab. Slab movement shall be monitored in accordance with Article 2539.05 of the standard specifications. Under no circumstances should underslab grouting cause the pavement slab to lift. Grout shall be pumped into each underslab grout port of each panel. Grout shall be pumped until it flows out of an adjacent grout port or until the line pressure on the grout pump reaches 5 psi. Grouting pressure of 5 psi may be exceeded (no greater than 15 psi) if the contractor can demonstrate that slab lift is not occurring at higher pressures.
The fluidity of the grout shall be checked at the beginning of each grouting operation and after each time the grout pump is flushed. Grout fluidity shall be checked in accordance with Article 2539.03 of the standard specifications. Fluidity shall be adjusted to achieve the necessary flow requirements to achieve full undersealing. If excessive bleeding of the grout is observed, the engineer may require the contractor to adjust the grout mixture.
Cleanup: upon completion of grouting, recesses in the surface of the panels at the grout ports shall be filled with an approved mortar and finished flush with the surface of the surrounding pavement. Any grout that flows onto the finished surface of the pavement during the grouting operation shall be immediately flushed from the surface. Any residual grout which hardens on the pavement surface shall be removed using an approved technique to the satisfaction of the engineer at the expense of the contractor.
Finished surface: the finished pavement surface shall be tested for smoothness by profilographing in accordance with Section 2316 of the standard specifications. Both lanes of the finished pavement shall be tested for smoothness. Corrective action to improve the profile index shall be accomplished by diamond grinding in accordance with Sections 2316 and 2532 of the standard specifications (grinding requirement of Section 2316 supersede Section 2532). Grinding depth shall not exceed 1/4 inch at the expansion joints. Grinding shall be performed with an abrasive grinding equipment, designed specifically for grinding pavement surfaces to close tolerances, utilizing diamond cutting blades with a minimum cutting width of 36 inches. Such equipment shall accurately establish slope elevations and profile grade controls. The final ground surface shall not be smooth or polished.