502Precast Concrete

Precast Concrete

502.1DESCRIPTION

1 This section describes the requirements for the design, fabrication, and construction of prestressed, precast concrete girders, precast concrete bridge members, and precast concrete box culverts.

2 The department will use the following definitions throughout this section:

cast curbs, shop-cast anchor bolts, bearing plates, shop- placed reinforcing steel, and other inserts and sleeves, as specified.

the precaster to provide the span lengths, structure widths, and girder depths specified.

502.2MATERIALS

1 Provide materials in accordance with the following:

Material Subsection

Admixtures 801.4 Aggregate 803 Elastomeric Bearing Pads 815.16 Fly Ash 801.2 Portland Cement 801.1 Prestressing Steel 811.5 Reinforcing Steel 811.1 Structural Steel 815.1 Water 814.1

502.3EQUIPMENT

1 Ensure hydraulic jacks used to stress tendons are equipped with either a pressure gauge or a load cell for determining the jacking stress. Equip jacks with an accurate dial with a diameter of at least 6 in [150 mm] or a digital display. Calibrate as a unit with the cylinder extension in the position it will be in at final jacking force and in accordance with the manufacturer’s recommendations. Ensure jacking equipment is calibrated annually. Re-calibration may be required if any jack or gauge gives erratic results or if the difference

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between the gauge reading and elongations exceed the allowable limits in accordance with Subsection 502.4.11, Prestressing. Ensure the gauge readings are accurate to within ± 2%.

502.4CONSTRUCTION

502.4.1 Plant Certification

1 Ensure that plants producing permanently installed precast (not prestressed) concrete items are certified by the National Precast Concrete Association (NPCA), America n Concrete Pipe Association (ACPA), or the Precast/Prestressed Concrete Institute (PCI) at the time of bid opening and manufacture. Ensure that plants producing prestressed precast concrete products are certified under the PCI Plant Certification Program, Category B4 at the time of bid opening and manufacture. Along with shop drawings, give the State Bridge Engineer a copy of the precaster’s certification, current at the time of manufacture.

2 If plants are changed, give the engineer a copy of the certification for the new plant at least seven calendar days before the fabrication of precast items to the project.

502.4.2 Shop Drawings

1 Before fabrication, ensure that the precaster gives the State Bridge Engineer shop drawings of each member showing complete details of the methods, materials, mix design including slump, equipment proposed for use in precasting, and the method and details of curing, in accordance with Subsection 105.2, Working Drawings. Include a written quality control plan. Submit welding procedure specifications for welding that will be incorporated into the finished member in accordance with Subsection 501.4.1.3, Shop Drawings.

2 For prestressed members, outline the following details:

devices; and

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in the members.

production number in the quality control documentation and material certifications, as applicable. Provide these production numbers on a member erection layout. Mark each completed member with the production number.

3 Do not begin fabrication without the State Bridge Engineer’s approval.

502.4.3 Design

502.4.3.1 General

1 When the precaster designs structural members, submit for approval two sets of design computations and for prestressed girders, girder camber along with the advance shop drawings to the State Bridge Engineer . Ensure that these design computations and the associated plans are prepared by or under the supervision of a professional engineer and in accordance with the latest edition of the AASHTO LRFD Bridge Design Specifications , including applicable interim revisions.

502.4.3.2 Prestressed, Precast Concrete Girders

1 Design prestressed, precast concrete girders in accordance with AASHTO bridge design specifications shown in the contract.

2 Provide bonded reinforcement in the top of the girder. Ensure a bonded reinforcement capable of resisting the total tension force in the concrete, computed on the assumption of an uncracked section. Ensure that tensile stresses in the concrete do not exceed 240 psi [1.7 MPa] before losses due to creep and shrinkage.

3 Provide calculations for elongation and include allowances for operations losses for the tensioning system used. These allowances must include losses for strand slippage, anchor movement, friction, strand rotation, and other forces acting on the strand.

502.4.3.3 Precast Concrete Box Culverts

1 Design precast concrete box culverts in accordance with the AASHTO bridge design specifications shown in the contract for the fill height specified; the State Bridge Engineer may approve alternate designs. Include provisions in the design for construction loads routed over the structures.

2 If the precast box culvert has cast-in-place concrete head walls and an alternate design with di fferent thickness walls is approved, submit revised head wall details with the precaster’s shop plans. Make changes in the structural concrete and reinforcing steel as a result of the alternate design at no additional cost to the department.

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502.4.4 Quality Control

1 The precaster is responsible for quality control. Ensure its performance by an inspector qualified by training and experience—of which, the State Bridge Engineer will be the final judge. Ensure that the primary job of the precaster’s inspector is quality control, independent of production. Ensure that the precaster’s inspector reports directly to the precaster’s top management or chief engineer and works separately from the production unit, performing no production or supervisory work for the project. Ensure that the precaster helps with inspection and gives the department’s inspector access to fabrication and storage areas.

2 Ensure that the precaster’s quality control plan outlines the steps the precaster will take to ensure that work meets specifications and that it lists the precaster’s inspection personnel.

3 Submit one copy of the project’s quality control documentation to the State Bridge Engineer after fabrication is complete.

502.4.5 Inspection and Records

1 Keep records providing full information regarding the testing of materials, tensioning, concrete proportioning, placing and curing, and disposition of members.

2 Ensure that the precaster’s inspection activities and records include the following:

steel, and cement and subassemblies, such as steel plates and their anchorages;

and the initial and final strand elongation measurements;

reinforcing steel; other incorporated materials; opening blockouts, etc;

and curing of the concrete;

air content, cylinder strength, etc;

handling and storing; and

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and other items affecting products.

3 Ensure that the precaster’s quality control personnel are responsible for keeping these records. Ensure that records are legible, complete, have the project identification, precaster’s name, and inspector’s name and signature.

502.4.6 Testing

1 Test concrete in accordance with Table 502.4.6-1, Precast Concrete Testing Requirements.

Table 502.4.6-1 Precast Concrete Testing Requirements Test Specification Slump AASHTO T 119 or ASTM C143 Air Content AASHTO T 152 or ASTM C231 Compressive Test Specimens AASHTO T 23 or ASTM C31 Compressive Strengths AASHTO T 22 or ASTM C39

502.4.7 Quality Assurance

1 The department’s inspector may provide independent inspection and may require a prefabrication conference with the precaster before beginning work. Before beginning work, give the department’s inspector two complete copies of all mill test reports, chemical analyses, and certifications required. Ensure that the precaster notifies the department’s inspector at least 14 calendar days before beginning work on precast concrete.

2 Review by the department’s inspector does not relieve the precaster of the responsibility for providing materials and finished members as specified. The department may reject deficient or defective materials or members at any time. Replace rejected items promptly at no additional cost to the department.

502.4.8 Concrete

1 Ensure that the precaster uses a design mix that produces concrete with the minimum specified 28-day compressive strength (f´C) and an air-entrainment of from 4.5 to 7.5 percent.

2 Measure and batch materials at a batch plant and to within ± 0.5 percent of the required individual material batch weight [mass].

3 Ensure that the precaster records temperature, entrained air, and slump before placing concrete in the forms. Keep complete records of quality control tests. Give a copy to the

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department’s inspector. Perform concrete control tests in the presence of the department’s inspector.

4 For testing 28-day acceptance strengths, ensure the precaster makes, for each precast member, at least three cylinders of concrete either 6 in [150 mm] diameter ×12 in [300 mm] high or 4 in [102 mm] diameter x 8 in [203 mm] high and cured in accordance with AASHTO T 23. Ensure that the precaster or an independent laboratory tests the cylinders and that transportation and curing (prior to and during transportation) of the cylinders is performed. Give test results to the department’s inspector. Cure cylinders taken for prestressed, precast members (to determine strength for form removal or for cutting or relaxing prestressing steel) by the same method and under the same conditions as the member. Ensure compressive testing machines are calibrated annually.

502.4.9 Reinforcing Steel

1 Ensure reinforcing steel is provided and placed in accordance with Section 514, Reinforcing Steel; ensure the precaster or an independent laboratory tests the samples. Give test results to the department’s inspector.

2 Ensure that the concrete cover to the face of main reinforcing steel is at least 1½ in [38 mm] and at least 1 in [25 mm] to other reinforcing steel.

502.4.10 Prestressing Steel

1 Protect prestressing steel against kinks, bends, nicks, broken wires , dirt, oil, or rust corrosion; visible rust or other signs of corrosion are cause for rejection.

2 Ensure the provision of a concrete cover at least 1½ in [38 mm] thick over the face of the prestressing steel, prestressing steel with a diameter less than or equal to 0.6 in [15 mm], and a center-to-center strand spacing of at least 2 in [50 mm].

3 Ensure that prestressing steel has been packaged in containers or shipping forms that protect against damage and corrosion and identify the manufacture r, type of steel, and heat number.

502.4.11 Prestressing

1 Tension prestressing steel with hydraulic jacks to at least the working stress shown in design computations. Do not cut or release prestressing steel in pretensioned members until the member has attained a compressive strength at least equal to the transfer value shown in design computations. Unless a load cell or other approved method is used to monitor stress in at least two strands, cast prestressed members on the same day as prestressing operations. Check for loss or prestress not more than three hours prior to placing concrete. Re-tension all strands to the original jacking stress that show a loss of prestress in excess of 3 percent.

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2 Measure the induced stress in the prestressing steel by gauge and check it by elongation, load cell, or both. Ensure the results are within 5 percent. Do not allow the jacking stress to exceed 75 percent of the specified minimum ultimate tensile strength of the prestressing steel. Measure the strand elongation to within 1 percent of the theoretical elongation or 1/16 in [2 mm], whichever is smaller. If a discrepancy between measured elongations and gauge reading exceeds 5 percent, check the entire operation before proceeding.

3 During stressing, individual wire failures may be accepted by the engineer, provided not more than one wire in any strand is broken and the area of broken wires does not exceed 3 percent of the total area of the prestressing steel in the member.

4 Use only oxygen flame or mechanical cutting devices to cut strands after installation in the member or after stressing. Do not use electric arc welders.

502.4.13 Bearing Devices and Embedded Items

1 Provide and install elastomeric bearing pads and embedded items in accordance with shop drawings.

2 Ensure that the precaster’s inspector verifies that elastomeric bearing pads and embedded items meet contract requirements by reviewing certifications and performing visual inspection.

3 Perform all welding to be incorporated into the final member in accordance with Subsection 501.4.1.11, Welding and Examination of Welded Joints.

502.4.14 Forms

1 Use metal forms for prestressed, precast members; use metal or wood bulkheads. Maintain metal forms in like- new condition with no open holes, dents, open joints, or misaligned butt joints. Fill open holes and joints with weld metal and grind smooth. Fill dents with weld metal and grind smooth or remove and replace with new metal welded in place and ground smooth. Make repairs so that the surface profile of the forms does not leave bumps or depressions in the cast concrete surface. Do not make temporary repairs using such materials as duct tape, caulking, etc. Ensure that forms produce a uniform surface finish for members and that form joints are smooth and tight enough to prevent significant leakage. Use forms rigid enough to prevent distortion from concrete pressure and other loads incidental to construction, including vibration. Before placing reinforcement, treat forms with an approved form release agent that will not discolor concrete. Before placing concrete, clean the forms of debris.

2 Chamfer exposed corner angles measuring less than 120 degrees with a ¾ in [19 mm] triangular strip. Chamfers are not required on edges that will be embedded in concrete. Use chamfer strips having no irregularities, and maintain joints with the chamfer tightly fitted against abutting forms.

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502.4.15 Placing Concrete

1 Mix and place concrete in accordance with Section 513, Structural Concrete, except vibrate the concrete internally, externally, or both, as required for proper consolidation.

2 Provide holes for diaphragm dowels and venting that pass through the member, openings for connection rods, and recesses for grout in members, as specified.

3 Lifting anchors may be installed in the ends of members, provided that the portion of each anchor above the concrete is removed after the member is erected. Show lifting anchors on shop drawings, and locate them with consideration for the safe handling and lateral stability of the member.

4 Do not remove prestressed precast concrete members from forms until the design transfer strength has been reached.

5 Do not “dry cast.”

502.4.16 Finishing Precast Concrete Surfaces

1 Do not add water to the surface of concrete to help in finishing operations.

2 Leave a rough finish to surfaces where additional concrete will be placed, a smooth surface where no additional concrete will be placed, and a transverse metal tine finish in accordance with Subsection 513.4.12.2, Finishing Bridge Decks, on deck surfaces where no additional concrete will be placed.

3 Give formed concrete surfaces an ordinary surface finish immediately after form removal. Remove and smooth fins and irregular projections. Thoroughly clean cavities produced by form ties and other holes, honeycombed spots, broken corners or edges, and other defects. Saturate with water and carefully point and true with a cement- and fine- aggregate mortar mixed as per the design mix or with a commercial patching mixture approved by the State Bridge Engineer. Apply mortar within 30 minutes after mixing. Cure mortar patches in the same manner as the concrete.

4 For prestressed precast concrete members, patch defects with an approved two- component epoxy resin concrete compound applied in accordance with the manufacturer’s recommendations. Match the finished color of the patch to the concrete.

5 Do not make concrete repairs, other than at hold-down locations for prestressed, precast concrete members, until the department’s inspector has been notified of the extent of irregularities and approved the method of repair.

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502.4.17 Curing Precast Concrete

1 Cure prestressed, precast concrete members by steam or alternate methods approved by the State Bridge Engineer . Cure other precast concrete members in accordance with Subsection 513.4.13, Curing Concrete, or by steam curing. Perform steam-curing as follows:

spray or wet blankets.

constructed to contain steam with minimum moisture loss. Use tarpaulins or similar flexible covers only if they are in good repair and secured to prevent steam and moisture loss.

impinge directly on the concrete, test cylinders, or forms. During application of steam, do not allow the temperature gradient within the enclosure to exceed 70 °F [20 °C] per hour. Maintain a constant curing temperature throughout the enclosure no greater than 160 °F [71 °C] for sufficient time to develop the required compressive strength. Cover control cylinders to prevent moisture loss and place in a location representative of the enclosure’s average temperature.

curing temperature; place one or more devices every 200 ft [60 m] of continuous bed length.

concrete and forms are still warm, or maintain the temperature in the enclosure above 60 °F [15 °C] until the stress is transferred to the concrete.

502.4.18 Tolerance for Precast Concrete Members

girders w ith tolerances shown in Table 502.4.18-1, Tolerances for Prestressed Precast Concrete Girders.

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Table 502.4.18-1 Tolerances for Prestressed Precast Concrete Girders Dimension Tolerance I-Girders T-, Bulb T-, and Tri- Deck Girders Depth: flanges, web, and fillets ±¼ in [±6 mm] ±¼ in [±6 mm] Depth: overall +½ in, -¼ in [+12 mm, -6 mm] ±¼ in [±6 mm] Width: flanges +⅜ in, -¼ in [+10 mm, -6 mm] +⅛ in, -¼ in [+3 mm, -6 mm] Width: web, fillets +⅜ in, -¼ in [+10 mm, -6 mm] +⅜ in, -¼ in [+10 mm, -6 mm] Length of beam ±¼ in/25 ft, 1 in max. [±1 mm/m, 25 mm max.] ±¼ in/25 ft, 1 in max. [±1 mm/m, 25 mm max.] Deviation along exposed beam ends (measure skews diagonally) ±3/16 in/ft, 1 in max. [±15 mm/m, 25 mm max.] ±⅛ in/ft, ½ in max. [±10 mm/m, 13 mm max.] Diaphragm insert spacing ±½ in [±12 mm] ±½ in [±12 mm] Stirrup bars: projection above top of beam ±½ in [±12 mm] n/a Stirrup bars: longitudinal spacing ±1 in [±25 mm] n/a Stirrup bars: clearance at end of beam ≤2 in [≤50 mm] n/a Horizontal alignment: deviation from a straight line parallel to centerline of beam ⅛ in/10 ft [1 mm/m] ⅛ in/10 ft [1 mm/m] Camber variation from design ±⅛ in/10 ft, ½ in max. up to 80 ft length [±1 mm/m, 12 mm up to 24 m length]; ±1 in max. over 80 ft length [±25 mm max. up to 24 m length] ±¼ in/10 ft, : in max. [±2 mm/m, 19 mm max.] Camber differential between adjacent beams n/a 1/4 in/10 ft [2 mm/m] 3/4 in [19 mm] max. Center of gravity of strand group ±¼ in [±6 mm] ±¼ in [±6 mm] Position of hold- down point for depressed strands ±6 in [±150 mm] ±6 in [±150 mm] Position of handling devices ±6 in [±150 mm] ±6 in [±150 mm]

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tolerances as follows:

2.1Internal dimensions within ± 1.0 percent of those specified;

2.2Haunch dimensions within ± ¼ in [6 mm] of those specified;

2.3Slab and wall thicknesses not less than 5.0 percent of those specified; and

2.4Lengths of two opposite surfaces of the box section within ± ¾ in [19

mm] of each other, except where bevel ends are specified.

502.4.19 Precast Concrete Box Culverts

1 Before shipping precast concrete box culverts, ensure the assembly of at least three sections, and that the joints fit as specified for final assembly. Record and report the gap dimensions to the engineer.

2 Excavate and backfill in accordance with Section 206, Excavation and Backfill for Culverts. Before installing precast concrete box culvert sections, obtain two copies of the recommended installation procedures from the precaster and give one to the engineer. Install on the prepared base in accordance with the recommendations.

3 Do not allow gaps between sections, when assembled in their final position, exceeding ½ in [12 mm] for more than 6 in [150 mm] at any one location or totaling more than 12 in [300 mm] in multiple locations. Do not allow the alignment of walls, top slabs, and bottom slabs to vary more than ½ in [12 mm] for more than 6 in [150 mm] at any one location or more than 12 in [300 mm] total in multiple locations. Measure misalignment perpendicular to slabs and walls.

502.

4.20Handling and Shipping Precast Members

1 Do not damage precast concrete members while handling, storing, or erecting. Blocking may be required to ensure safe transport. Handle, store, and erect members in an upright position and such that the points of support and directions of the support reactions with respect to the member are approximately the same as when the member is in its final position. Until concrete has attained 75 percent of the specified design strength, do not move precast members by lifting on anchors embedded in the concrete or by lifting the member itself.

2 Mark the weight [mass] on members heavier than 3 ton [2.7 t].

3 Ensure that materials shipped to the project are accompanied by a manufacturer’s certification that lists each separate piece by name and piece mark and includes mill test reports and the precaster’s quality control report.

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4 Determine and provide the necessary temporary bracing to ensure lateral stability of prestressed, precast concrete girders during erection and placement of the diaphragms and deck. Do not remove temporary bracing until the deck is placed and the diaphragms have attained 80 percent of ultimate design strength.

502.4.21 Rejection of Precast Members

1 The department may reject precast members if, upon removal of the forms, there is cracking, honeycombing, air pockets, sand streaks, or other evidence of imperfect mixing or casting or because of failure to meet requirements of these specifications at the fabrication plant or job site.

502.5MEASUREMENT and PAYMENT

1 The engineer will measure:

Girder ____ in [mm], and Prestressed Precast Conc Tri-Deck ____ in [mm] by the foot [meter] from end of girder to end of girder for each prestressed precas t member supplied.

2 The department will pay as follows:

Pay Item

Pay Unit Measure to the Nearest Pay to the Nearest Precast Box Culverts × × ft [mm] FT [m] 0.1 ft [0.05 m] FT [0.5 m] Precast Concrete Members LS LS LS Prestressed Precast Conc Bulb-T in [mm] FT [m] 0.1 ft [0.05 m] FT [0.5 m] Prestressed Precast Conc I-Girder in [mm] FT [m] 0.1 ft [0.05 m] FT [0.5 m] Prestressed Precast Conc Tri-Deck in [mm] FT [m] 0.1 ft [0.05 m] FT [0.5 m]