Section 708. PRESTRESSED CONCRETE BEAMS Description. Manufacture and erect prestressed concrete beams.

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1 708.0 Section 708. PRESTRESSED CONCRETE BEAMS Description. Manufacture and erect prestressed concrete beams Materials. Use materials meeting the following. Mortar and Grout Cement Coarse Aggregate 6AA, 7A Fine Aggregate 2NS Admixtures and Curing Materials Air-Entraining Admixtures Chemical Admixtures, Types A, D, F, and G FlyAsh Prestress Strand Post-tensioning Strand or Bar Reinforcing Steel Steel Welded Wire Steel Welded Wire Fabric Structural Steel Water... 9 Use natural aggregate for 6AA or 7A aggregate according to subsection Natural aggregate 7A may be substituted for 6AA if the 7A natural aggregate meets the physical requirements of 6AA according to table and has a maximum freeze-thaw dilation of 0.00 percent per 00 cycles. Base freeze-thaw test results on 6AA gradation. Use non-deformed steel rods according to AASHTO M 83 as position dowels for precast beams and hot-dip galvanize according to AASHTO M 232. Use prestress strand free of oil, dirt, paint, rust and other results of corrosion, and foreign material that may prevent bond between the strands and the concrete. Do not use a reel or pack of strand if one or more wires in the strand show a coating of adherent rust that light rubbing cannot remove. Do not use strand that contains adherent rust, pits visible to the naked eye, kinks, bends, nicks or other defects. Cover prestress strand stored outside with waterproof tarps and block above the ground to prevent contact with soil and water. Do not use strand without identification. 444

2 Select a debonding compound for the prestressed concrete 800 beam flange from the Qualified Product List or provide an approved equal. Follow the manufacturer s specifications and procedures for mixing the compound. Use a compound color that when cured, will contrast with beam flanges enough to show evidence of application Construction. A. Construction of Prestressed Beams.. Plant Certification. Use plants certified by the Prestressed Concrete Institute for Category B3, Prestressed Straight Strand Concrete Members or Category B4, Prestressed Draped Strand Concrete Members. Use plants certified as Category B4, Prestressed Draped Strand Concrete Members when fabricating products that require draped strands. Immediately correct items not conforming to PCI plant certification. Furnish a copy of the certificate of conformance to the Engineer before the start of production. Clearly display the certification of conformance in each plant facility. Provide facilities for inspection according to section 809 and subsection A Shop Plans. Submit shop plans according to subsection Show complete fabrication details and initial prestressing forces. Send three sets of drawings to the Engineer for review and acceptance. Do not start production until the Engineer has accepted the shop plans. 3. Notifying the Engineer. Notify the Engineer at least one week before manufacturing concrete beams. 4. Equipment. a. Forms. Use metal forms. However, use wood forms for bulkheads if desired. Forms must meet subsection D. b. Specimen Molds. Use specimen molds for making test specimen according to ASTM C 470. c. Curing Tank. Provide an approved curing assembly consisting of a water tank equipped with thermostatic controls. Maintain limesaturated water at 70 ± 5 F. Size the tank to contain the 28- day test specimens. 445

3 d. Compression Testing Machine. Provide a compression testing machine according to ASTM C 39. Submit a certificate of calibration, not more than 2 months old, to the Engineer. 5. Void Boxes, Inserts, and Attachments. Fasten void boxes, inserts, and attachments to maintain the proper position during concrete placement and compaction. Design and construct to withstand the forces imposed during fabrication without substantial deformation such as bulging, sagging, or collapse. Place weep-holes to provide drainage for all voids. 6. Design and Proportioning of Concrete Mixtures. Design a concrete mixture meeting the following requirements: a. 6.5 ±.5 percent air except as allowed in e. b. 28-day compressive strength as shown on the plans. c. Slump of not less than 3 4 inch nor more than 2 2 inches when no water-reducing or retarding admixture is used. d. Slump of not more than 4 inches when a Type A or a Type D chemical admixture is used. e. Slump of not more than 7 inches and an air content not more than 8.5 percent when a Type F or a Type G chemical admixture is used. f. Minimum of 564 pounds of cementitious material (cement plus fly ash, if used) per cubic yard of concrete. Use fly ash at no more than 20 percent of the total weight of cementitious material. 7. Concrete Strength. The Engineer will base acceptability of the concrete for strength on the results of compressive strength tests on standard 6 by 2 inch cylinders. All costs associated with molding, storing, and testing the cylinders will be borne by the Contractor. a. Molding and Curing. Make a minimum of six test cylinders from concrete for each prestressed beam line. Make one third of the cylinders from each of three separate batches or loads of concrete used in casting each beam line. An additional set of three cylinders may be molded and cured to determine strength for acceptance of the concrete at less than 28 days. Mold and cure the cylinders according to ASTM C 3, except as modified here. Leave all the cylinders with the beams or in the 446

4 curing enclosure until stripping the member. Then, remove the 28-day cylinders from their molds and place in a water curing tank until testing. Leave the remaining cylinders with the beams until testing. b. Testing and Acceptance. Conduct all compressive strength tests in the presence of the Engineer. Test according to ASTM C 39, except test the specimens in the moist condition resulting from the specified curing conditions. Use one set of three test cylinders to determine the time of transfer of stress from the end anchorages to the concrete. Test the optional set of test cylinders at any time before the end of the 28-day curing period. Test all three cylinders of this optional set at the same time. The Engineer will accept these optional cylinder results, in place of the 28-day tests, if they equal or exceed the 28-day strength requirements. If the optional cylinders do not meet or exceed the 28-day strength requirements, continue curing the remaining set of three test cylinders for the full 28-day period. Test the remaining three cylinders at 28 days to determine the acceptability of the strength of the concrete. Do not ship beams until they have met the 28-day strength requirements. The compressive strength of the test specimens must meet both of the following conditions. The average of the compressive strength of the three test specimens must be at least equal to the required minimum compressive strength. At least two of the three specimens must meet the required minimum compressive strength and the third specimen must have at least 60 percent of the required minimum compressive strength. If these criteria are not met, the Engineer may either reject the beam(s) represented by these tests or determine if the concrete has sufficient structural strength, and if so, prorate the unit price for the pay item and quantity represented based on formula. 447

5 Adjusted Tested Strength X Unit Price Formula 708- = unit price Required Strength 8. Placing Reinforcing Steel. Securely tie reinforcing steel. Do not tack weld steel reinforcement. 9. Bond Breaker. When a bond breaker is required, use two tubes (one inside the other) and turn the overlap in opposite directions. 0. Placing Concrete. Place concrete according to subsection H, with the following modifications. a. Use external vibrators if desired. b. Protect fresh concrete from rain. Cover the forms during the interruption of casting operations because of rain. c. Maintain a concrete temperature between 45 and 90 F, as near 70 F as practical, during placement.. Curing Beams. Protect concrete from cold weather. Construct the curing enclosure to allow circulation of air or steam around the exposed portions of the beam. Cure the beams between 70 and 60 F until the concrete attains the release strength shown on the shop plans. Maintain the required temperature during the curing period with steam or radiant heat. Apply steam or radiant heat after concrete has reached its initial set according to ASTM C 403, and do not damage the concrete. During the waiting period, maintain the ambient temperature in the curing enclosure between 50 and 70 F. Do not direct steam or radiant heat on the concrete or on the forms causing localized high temperatures. During the initial application of steam or radiant heat, increase the ambient temperature within the curing enclosure at no more than 80 F per hour (.33 F per minute) until reaching the desired curing temperature. Hold the maximum curing temperature within the enclosure until the concrete has reached the desired temperature and strength. Do not exceed a maximum concrete temperature during the curing cycle of 95 F. When curing is complete, reduce the ambient temperature within the enclosure at no more than 80 F per hour (.33 F per minute). 448

6 Provide recording thermometers when using steam or radiant heat curing, that show the time-temperature relationship within the curing enclosure from the time concrete is covered until transfer of prestress. Graph all time-temperature documentation and provide a copy to the Engineer for evaluation. Use at least two recording thermometers per product line, at locations determined by the Engineer, to monitor the concrete and the curing rate. 2. Cracks in the Beams. The Engineer will evaluate cracked beams for acceptance. 3. Workmanship. a. Concrete Defects. Immediately after removing the forms, patch air holes larger than one inch with Type R-2 mortar, as directed by the Engineer. The Engineer will evaluate beams with honeycomb areas for acceptance. b. Finishing I-Beams. Smooth finish the outer inch of the top surface of the beam. Rough finish the remainder of the top surface of the I-beams to give a 4 inch surface texture. c. Finishing 800 Beams. Smooth finish the outer 6 inches of the top surface of the beam. Rough finish the remainder of the top surface of the I-beams to give a 4 inch surface texture. Clean the outer 6 inches of the top surface and apply a debonding compound according to the manufacturer s recommendations. Prevent compound from spreading over the beam flange or toward the center of the beam. Remove all compound that has exceeded the 6 inch boundary before it has cured. Use solvents approved by the debonding compound manufacturer. d. Finishing Box Beams. Smooth finish the outer inch of the top surface of the beam. Rough finish the remainder of the top surface of box beams to give a 4 inch surface texture unless a hot mix asphalt overlay is specified then give the top surface a wood float finish. e. Sole Plates. Hot-dip galvanize sole plates according to AASHTO M 232. f. Bearing Surfaces. Correct divergences in all bearing surfaces greater than 8 inch in 2 inches. 449

7 4. Tolerances. The Engineer will evaluate beams that do not conform to the dimensional tolerances in Table Table 708- Dimensional Tolerances for Beams Length of I-Beams and 800 Beams Length of Box Beams Width of I-Beams and 800 Beams Width of Box Beams Height of I-Beams, 800 Beams, or Box Beams Camber Deviation From Design Value (Measured Within 24 Hours of Strand Release) Thickness of Top Slab of Box Beam Length of I-Beam End Blocks Sweep of I-Beams and 800 Beams (Horizontal Deviation of Centerline from a Straight Line Between Ends Measured at Both Top and bottom) Sweep of Box Beams (Horizontal Deviation of Centerline from a Straight Line Between Ends Measured at Both Top and Bottom) Vertical Deviation of Side Forms Between Top and Bottom of Beam Prestress Strand Location of Conduit for Transverse Post Tensioning Location of Holes for Position Dowels (I-beams and 800 Beams) Location of Holes for Position Dowels Box Beams ± 4 inch per 25 feet, inch max ± 3 4 inch + 2 inch, - 8 inch ± 2 inch + 4 inch, - 8 inch 8 inch per 0 feet + 2 inch, - 4 inch + 2 feet, -0 inches 4 inch per 0 feet 3 8 inch up to 60 feet, 2 inch over 60 feet 4 inch maximum from plan location 4 inch maximum from plan location 2 inch maximum from plan location 2 inch maximum from plan location inch maximum from plan location 5. Stress Transfer. Do not transfer bond stress to the concrete nor release end anchorages until the concrete has attained the specified compressive release strength. Cut or release prestressing cables so that lateral eccentricity of prestress is minimized. After detensioning the cables, cut them flush with the surface of the concrete and cover the ends and all depressions around the ends of cables with an asphaltic material approved by the Engineer. 6. Handling, Storage, and Transporting Beams. Handle and store the beams to prevent damage. Keep the beams upright. When moving a beam, lift it by the loop devices detailed on the plans, unless alternate lifting devices and procedures are approved by the Engineer. Apply equal loads to each pair of lifting devices. 450

8 Support stockpiled beams across their full width on two battens more than 4 inches wide. Never support beams at more than two points. Use battens high enough to hold the beam off the ground over its full length. Place battens in from the beam ends a distance not to exceed 2 times the depth of the beams or 3 feet, whichever is less. For skew beams, measure this distance along the centerline of the beam. Place battens supporting beams stacked one above the other, in the same vertical plane at each end of the beams. Support beams during transport the same as stockpiled beams. However, trucks with two rear bolsters may be used. Use wood shingles to give proper bearing if truck bolsters are worn. Place wood blocks under chains used to hold the beams in place on the trucks. B. Erection of Prestressed Beams.. Box Beams. Shim beam bearing pads during erection, as necessary, to provide full bearing contact with the bottom of the beam. Place seal washers, or other devices meeting the approval of the Engineer, between the beams at the transverse conduit holes. After the beams are set, drill position dowel holes into the bridge seats through the holes provided in the ends of each beam. Insert the dowels. At the expansion bearings, fill the position dowel holes with hot-poured rubber-asphalt type filler to at least 3 inches above the position dowels; fill the remainder of the hole with Type H- grout. Fill the holes at fixed bearings with Type H- grout. After the beams are firmly set in their final position, clean with water and grout the longitudinal joints and the surfaces between the beams. Use Type R-2 grout with a slump of approximately 5 inches and place when the air temperature is above 40 F. Fill the space between the beams full-depth. Rod the grout into the space to form a tight, solid joint. Cure for 48 hours. After the grout has cured, post-tension the deck transversely. Tension the tendons to the force shown on the contract drawings; however, do not exceed the yield stress of the material. After tensioning, clean the annular space between the tendon and the hole by flushing with water and remove the water with compressed air. With the grouting vent open at one end of the hole, inject Type E- grout under moderate pressure at the other end. Continue injecting grout until the material comes out through the 45

9 open vent. Close the open vent while maintaining pressure. Gradually increase pressure to at least 50 psi and hold for approximately 5 seconds, close the inlet valve. Remove lifting devices. 2. I-Beams and 800 Beams. Place I-beam bearing pads over the position dowel and shim, as approved, to provide full bearing contact with the bottom of the beam. Position the beams on the substructure and rigidly block them in place before proceeding with deck and diaphragm forming. Remove lifting devices Measurement and Payment. Contract Item (Pay Item) Pay Unit Prest Conc Deck, inch...square Foot Post Tensioning (Structure No.)... Lump Sum Prest Conc Box Beam, Furn, inch.... Foot Prest Conc Box Beam, Erect, inch... Foot Prest Conc I Beam, Furn, inch.... Foot Prest Conc I Beam, Erect, inch... Foot Prest Conc 800 Beam, Furn... Foot Prest Conc 800 Beam, Erect.... Foot A. Payment for prestressed concrete beams erected includes position dowels, shimming to provide full bearing contact, and bracing and blocking as required. B. Prestressed concrete box beams that are placed a nominal distance of 2 inches apart will be measured as Prest Conc Deck by area, based on the nominal overall length of the units multiplied by the overall plan width. Plan width is the sum of the widths of the beams plus the sum of the 2 inch spaces between the beams. C. Post Tensioning includes all labor, equipment, and materials necessary to complete the work as described. D. Prestressed concrete box beams placed greater than a nominal 2 inches from each other will be measured as Prest Conc Box Beams by length, based on the nominal overall length of the units. E. Prest Conc I Beams and Prest Conc 800 Beam, will be measured by length based on the nominal overall length of the units. Payment includes debonding the beam flanges. 452

10 F. Elastomeric bearings will be measured and paid for according to subsection G. Costs incurred in the certification of prestressed concrete plants are the responsibility of the Contractor/Fabricator and no additional compensation is allowed. Claims by the Contractor for delays or costs associated with prestressed concrete fabrication plant certification will not be allowed. 453

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03450 ARCHITECTURAL PRECAST CONCRETE *************************************************************************************************************** SPECIFIER: CSI MasterFormat 2004 number 03 45 13 ***************************************************************************************************************