1108POST-TENSIONING OPERATIONS

1108.01GENERAL REQUIREMENTS—

Department, either in a pre-stressing plant or on the project site. Retain a Professional Engineer, registered in the State and experienced in post -tensioning operations, to be present and in charge of tensioning and grouting operations. Submit, in writing, the Engineer's name and the date and place of post-tensioning to the Structure Control Engineer 3 weeks before the start of the post-tensioning operations. A Professional Engineer, registered in the state is not necessary for post - tensioning box culverts or transversely post-tensioning adjacent box beam bridges. At the approval of the District Structure Control Engineer, post-tensioning operations may be done under the direct supervision of a qualified supervisor maintaining an active Post-Tensioning Institute (PTI) Bonded Post-Tensioning Level 2 certification with a minimum of 3 years of related experience instead of the use of a Registered Professional Engineer. At the approval of the District Structure Control Engineer, grouting operations may be done under the direct supervision of a qualified supervisor maintaining an active American Segmental Bridge Institute (ASBI) Grouting Certification with a minimum of 3 years of related experience instead of a Registered Professional Engineer. Submit, in writing to the Structure Control Engineer, the grouting crew’s verifiable experience three weeks before grouting operations. At a minimum two of the grouting crew members and the grout pump operator must have current ASBI certifications.

Show the proposed method, material, and equipment including a ll changes to reinforcing steel. Shop drawings must show the following:

• method and sequence of stressing including complete specifications

• details of the pre-stressing steel

• details of the anchoring devices, bearing devices, location of splices or couplings,

• details of the working stresses, anchoring stresses,

• type of ducts,

• steel corrosion protection,

• proposed arrangement of the pre-stressing steel in the members,

• pressure grouting- material and equipment, and

• vent details including size, type, spacing, and location and direction of grouting.

Provide a detailed stressing force diagram showing the following:

• deviations from design forces;

• sequence of loading stages;

• friction coefficients for the duct and tendon combinations;

• friction and jacking forces;

• jacking techniques, e.g., overjacking;

• friction loss diagram, superimposed on the force diagram; and

• elongation computations.

Provide shop drawings that are signed, dated, and sealed by a Professional Engineer , registered in the State. Unless indicated or specified, do not use a working stress greater than 0.6 fu, a temporary stress greater than 0.75 fu, or an anchoring stress greater than 0.7 f u (fu = specified minimum ultimate tensile strength of pre-stressing steel). Working force and working stress are the force and stress remaining in the pre-stressing steel after losses including concrete creep and shrinkage, elastic concrete compression, steel losses due to stressing sequence, steel relaxation, friction and take up at anchorages, and other losses peculiar to the pre-stressing system.

1108.02MATERIAL—

1107.02(n)

in Bulletin 15. Submit the grout mixture to the DME/DMM for review and approval before use. Certify as specified in Section 106.03(b)3.

Design couplings to develop 1.0 fu. Use bearing devices designed to transmit the anchor force to the concrete at bearing stress no greater than 3,000 pounds per square inch. Limit bearing device stress to 80% of its yield strength if the pre-stressing steel is stressed to 0.95 fu. Certify as specified in Section 106.03(b)3.

steel sheathing. PVC plastic ducts, corrugated seamless polypropylene plastic duct, or smooth HDPE ducts may be used only if sufficiently secured to prevent internal bowing or sway. Certify as specified in Section 106.03(b)3. Minimum duct thickness for metal ducts must be as follows:

• Strand tendons. 26-gauge diameter for ducts less than or equal to 2.625 inches in diameter and 24 gauge diameter for ducts greater than 2.625 inches in diameter

• Bar tendons. 31-gauge diameter

corrosion protected, pre-stressing strand for unbonded post-tensioning comprised of the following components:

2.a Material. Polypropylene, cell classification PP 210 B55542, conforming to ASTM D4101, or polyethylene, High Density Type II, conforming to ASTM D3350 and ASTM D1248.

2.b Thickness and Diameter . Provide a minimum sheathing wall thickness of 0.05 inch and an inside diameter of 0.03 inch greater than the maximum diameter of the strand.

2.c Application. Apply around pre-stressing strand in a seamless hot -melt extrusion process. Provide a smooth, circular outside with no visible reveal of the lay of the strand.

3.a Material Properties. Provides corrosion protection to the strand; lubrication between the strand and sheathing; continuous non-brittle coating if exposed to a temperature of -10F; resists flow within temperature range of -10F to 110F; and chemically stable and nonreactive with pre-stressing strand, reinforcing steel, sheathing material, and concrete.

3.b Quantity. Not less than 2.5 pounds per 100 feet for 0.5 -inch diameter strand and 3.0 pounds per 100 feet for 0.6 -inch diameter strand. Completely fill the annular space between the strand and sheathing along the entire length of strand.

3.c Performance Criteria. Table A.

TABLE A Performance Specification for Corrosion Inhibitor Compound Test Description Test Method Acceptance Criteria Dropping Point ASTM D566 or ASTM D2265 Minimum 300F Oil Separation at 160F FTMS (Federal Test Method Standard) 791B Method 321.2 0.5% max by weight Water Content ASTM D95 0.1% maximum Flash Point (refers to oil content) ASTM D92 Minimum 300F Corrosion test (5% salt fog at 100F 5 mils) ASTM B117 Rest Grade 7 or better after 1000 hours of exposure according to ASTM D610 Water-solubleions *

ASTM D512 ASTM D3867 APHA (American Public Health Association) 4500-S2E

10 ppm maximum 10 ppm maximum 10 ppm maximum Soak test (5% salt fog at 100F 5 mils coating, Q Panel TypeS. Immerse panels 50% in a 5% salt solution and expose to salt fog) ASTM B117 (modified) No emulsification of the coating after 720 hours of exposure. Compatibility with sheathing

after exposure of polymer to grease, 40 days at 150F

of polymer after exposure to grease, 40 days at 150F

ASTM D4289 (ASTM D792 for density)

ASTM D638

Permissible change in hardness 15%, volume 10%.

Permissible change in tensile strength 30%.

* Procedure: The inside (bottom and sides) of a 1 L calibrated, graduated beaker (approximate outside diameter 105 mm, 145 mm height) is thoroughly coated with 100 ± 10 g of corrosion inhibitor compound. The coated beaker is filled with approximately 900 cc of distilled water and heated in an oven at a controlled temperature of 38 °C ± 1° for 4 hours. The water extraction is tested by the noted test procedures for the appropriate water-solubleions. Results are reported as ppm in the extracted water.

1108.03CONSTRUCTION—

Do not use pre-stressing steel with sustained physical damage, pitting, or rust that cannot be removed by wiping with a dry cloth. Do not retain pre-stressing steel in an ungrouted duct for more than 14 days without special acceptable corrosion protection. Pack pre-stressing steel in containers or other shipping forms for protection against physical damage and corrosion during shipping and storage. Place a corrosion inhibitor that prevents rust or other corrosion in the package or form or, if allowed, apply it directly to the steel or tendon. Mark on the shipping package or form that the package contains high-strength, pre-stressing steel and the care to be used in handling. State the type, kind, and amount of corrosion inhibitor used, including placement date, safety orders, and instructions for use. When stressing and grouting are completed within 10 calendar days after the pre-stressing steel installation, rust that may form will not be cause for rejection. In this case, use of a corrosion inhibitor is not necessary. Before use, submit the coating system for tendon corrosion protection in a bonded system for approval. Protect bar tendons from corrosion at the job site by spraying with a rust preventative and by use of an approved protective covering over the bars.

at the ends. Steel distribution plates or assemblies may be omitted if large enough anchorages are used in conjunction with a steel grill embedded in the concrete to effectively distribute the compressive stresses to the concrete. For all systems of post-tensioning, set each anchorage device in all directions perpendicular to the pre- stressing steel axis. At both tendon ends, make accurate measurements of anchorage loss due to slippage or other causes. Compare these losses with the assumed losses shown in the post-tensioning schedule on the shop drawings. If necessary, make adjustments or corrections in the operation to reduce loss or slippage. For special anchorage devices, test according to AASHTO LRFD Bridge Construction Specifications , Section 10.3.2.3.

concrete is placed. Make splices grout-tight. After installation, blow the ducts clear using oil-free, compressed air for at least 5 seconds each. Plug the duct ends to prevent the entry of water or debris. Make all splices, joints, couplings and connections to the duct and anchorages with devices or methods (mechanical couplers, plastic sleeves, heat -shrink sleeve) producing a smooth interior alignment with no lips or kinks. Use plastic welded connections on plastic sleeves and splices or u se heat-shrink sleeves at the connections to seal seams. Connections must be sealed to prevent leakage. Provide ducts or anchorage assemblies with pipes or connections for grout injection. Install 1/2 inch or larger in size pipe vents near the high points of each duct. Make vents grout-tight and provide means for grout injection, and heat-shrink wrap as necessary. Remove vent ends 1 inch below the member surface, after grouting has been completed. For tendons made up of single pre-stressing bar or strand, make the inside diameter at least 1/4 inch greater than the diameter of the pre-stressing bar or strand. For tendons consisting of several pre-stressing strands, make the duct's cross-sectional area at least 2.5 times the net area of pre-stressing steel. Locate ducts within the specified tolerances. For curved members, place the ducts on, or symmetrically about, the member axis parallel to the curvature direction.

Provide concrete cover a minimum of 1 1/2 inches for sheathing up to 2 inches O.D., and a minimum of 2 inches of cover for larger sheathing. Provide a minimum of 1 1/2-inch clear spacing between the sheathing at the beam ends, or provide 1 1/2 times the maximum aggregate size, whichever is greater. After the pre-stressing steel has been installed, do not weld or use as a ground for welding equipment on steel in the member. Do not flame cut unless the ducts and tendons are effectively shielded.

steel is not less than the value indicated on the accepted shop drawings with appropriate allowance for all losses. Within 20 days before stressing, calibrate all jacks and pressure gauge system and furnish certified copies of the load calibration curves to the Engineer except jack calibration for post-tensioning of box culverts and adjacent box beams. For post-tensioning of box culverts and adjacent box beams, accompany jack gauges with a current, certified calibration chart not older than 6 months. Equip each jack with a pressure gauge having an accurate reading dial at least 6 inches in diameter. Calibrate each ja ck and its gauge as a unit with the cylinder extension in four separate locations based on the final jacking force. Calibrate the jack and its gauge in the approximate 1/4 stroke, 1/2 stroke, 3/4 stroke, and final stroke position. Recalibrate stressing equipment at 6-month intervals, after mechanical failure, and if the accuracy of the stressing equipment is called into question by the Representative . Do not interchange jacks and gauges without recalibration. Check the certified calibration chart for hydraulic jacks and pressure gauges used for tensioning pre-stressing steel, both before and during tensioning operations. Do not stress tendons until the concrete has attained its 28-day strength unless partial stressing is allowed at a lower strength. Apply an initial load of 10% of the full load to the tendon to take up slack and to provide a starting point for measurement of elongations. Apply the final load, including any overload. Apply the load at a rate consistent with procedures recommended by the manufacturer of the system. Unless otherwise indicated, in simple span members, stress by jacking from one end only, with one-half of the pre-stressing steel in each member tensioned from one end and the other one -half tensioned from the opposite end. If the same tendons are jacked from two ends, both jacking operations may be done simultaneously, provided uniform tensioning forces are applied at each end. The stressing forces, measured by jacking pressures and elongation, are required to agree within 5%. If the measurements cannot be reconciled within this range, halt the stressing, examine the procedure, and determine the sources of error so the measured force can be verified within this limit. If sources of error cannot be determined or verified by the Professional Engineer in charge of post-tensioning operations, to the satisfaction of the Engineer, the post-tensioning of the member will be stopped and the member rejected. In continuous members, tension by jacking at each tendon end, unless otherwise indicated. Jacking of both ends need not be done simultaneously, unless otherwise indicated.

grout. Alternate grouts consisting of Type I, II, or III Portland cement may be used if an approved Special Design Grout, Class D is provided by the Design Engineer and conforms to the requirements of the Post- Tensioning Institute (PTI) M55.1 Section 3.4. Class D grouts must use non-shrink admixture and anti-bleed admixture of the type recommended by the manufacturer of an accepted tendon. Do not use admixtures containing chlorides or nitrates, or that release free hydrogen. Use enough grout plastic to pump and completely fill the ducts. No grout shrinkage is allowed while in the plastic state. Before post -tensioning, submit the Manufacturer’s data sheet of the grout to be used . to the Structure Control Engineer. If using a Class D, Special Design Grout, submit the mix design to the DME/DMM a minimum of two weeks before grouting. D esign the mix and verify it has a minimum compressive strength of 2,500 pounds per square inch at 7 days and has 4% to 10% expansion. Verify strength by testing according to ASTM C109. Limit the water content of the grout to the minimum volume necessary to produce a mix that can be pumped, with a maximum of 5 gallons per bag of cement or grout according to manufacturer’s recommendations, whichever is less. Prepare test cylinders from each day's grouting. Visually determine the grout's ability to be pumped. Strength testing of grout for precast box culverts is not required.

1.a. Quality Control Testing. perform the following tests for each pump used for each shift or if a change in pump operator occurs. Testing must re-occur if visual or apparent changes in the characteristics of the grout occurs.

• Fluidity Test. ASTM C939, Modified . Once every 2 hours, at the inlet. Results must be within 5 seconds of values established for grout qualification.

• Schupack Pressure Bleed Test. ASTM C1741. Once per day, per shift at the inlet.

• API Mud Balance Test. Two (2) per day, at both the inlet and outlet. Result must be between the values for minimum and maximum water dosage.

• Change in Volume Tests (if expansive agent is used). ASTM C1090. Once per day. 0.0% +/- 0.1% change in 24 hours max, +0.20% change at 28 days.

• Grout Strength. ASTM C942. Once per day, per shift at the inlet.

per square inch. Furnish equipment with a pressure ga uge that has a full -scale reading of not more than 300 pounds per square inch. Provide standby flushing equipment and compressed air equipment capable of developing a pumping pressure at 250 pounds per square inch and large enough to flush out partially grouted ducts. Provide working pressure meterss that show the grout pressure at the injector nozzle discharge end on the group pumps.

grouting procedures. After curing, blow ducts free of water and keep them dry until grouting. Immediately before grouting, blow the ducts out with oil-free compressed air. Mix the grout using a high-shear colloidal mixer that produces uniform and thoroughly mixed grout. Do not retemper grout. Agitate the grout continuously until it is pumped. Before entry into the pump, screen grout through 0.07-inch maximum, clear opening screen. Grout the ducts after completion of the tensioning operation for each unit as specified in Section

(b), unless otherwise directed

Equip grout injection pipes with positive, mechanical shutoff valves. Fit vents and ejection pipes with valves, caps, or other devices capable of withstanding the pumping pressures. Do not remove or open valves and caps until directed, generally after the grout has set. Apply grout by pumping toward open vents. Pump continuously, approximately 15-50 ft per minute, using moderate pressure , not to exceed 145 pounds per square inch for plastic ducts or 245 pounds per square inch for steel ducts, at the entry point in the duct, until entrapped air is forced out the open vent or vents and until visible slugs of water or air are ejected. Close the outlet pipe only after sufficient grout, equivalent to the grout being injected at the inlet, is ejected from the outlet . With the entire duct filled and discharge vents closed, raise the pressure to a minimum of 50 pounds per square inch and hold for a minimum of 1 minute, and then plug the injection point to prevent grout loss. Close the valve at the inlet while maintaining this pressure.

3.a. For box culverts: Close discharge vents while applying constant grouting pressure from the injection point. Once all discharge vents are closed, close the valve at the injection point and disengage the pump . Do not apply an increase in pressure after all discharge vents are closed. Using an abrasive, blast clean the concrete surfaces at anchorage assemblies, until clean aggregate is exposed, to ensure concrete bonding or grout encasement of assemblies. Where the end of a post-tensioned assembly is not embedded in concrete, recess the anchorages so the pre-stressing steel ends and parts of the anchorages will be at least 2 inches inside of the member end surface, unless a greater embedment is indicated. Following post -tensioning, clean the recesses, fill with non-shrink mortar, and finish flush. After curing, paint surfaces with two coats of epoxy resin.