00555.00 508 Section 00555 - Post -Tensioning
Description
00555.00Scope - This Work consists of post -tensioning cast -in-place and precast concrete by
furnishing, placing and tensioning stressing steel according to details shown and specified. This Work also includes furnishing and installing any items necessary for the stressing system used including, but not limited to, anchorage assemblies, ducts and grout for pressure grouting. Concrete that is to be stressed by the post -tensioning method will be referred to as a member.
00555.03Anchorage Devices - Secure all post -tensioned stressing steel at the ends by means of
approved permanent type anchorage devices. Design anchorage devices according to the current AASHTO LRFD Bridge Design Specifications . Identify post -tensioning anchorage systems as either "Normal Anchorage Devices" or "Special Anchorage Devices" as defined in the AASHTO LRFD Bridge Design Specifications . Provide anchorage devices that meet all testing and construction requirements of the AASHTO LRFD Bridge Design Specifications and the AASHTO LRFD Bridge Construction Specifications . Equip all anchorages with a permanent fiber reinforced plastic grout cap that encloses the whole wedge plate. Provide a grout cap that is vented, bolted to the anchorage and rated for a minimum pressure of 145 psi. Seal the group cap to the anchor plate using either a neoprene gasket or epoxy bonding agent. For bearing plates, provide 7 inch minimum edge distance from the top of deck and 2 inch minimum edge distance from expansion joint blockouts and any other concrete edge.
Install 3 piece anchor wedges in all permanent post -tensioning applications.
Materials
00555.10Materials - Furnish Materials meeting the following requirements:
Anchorage Devices .................................................................. 02530 and 02540 Couplings .............................................................................................. 02515.60 Tendon Duct .......................................................................................... 02515.50
00555.11Stressing Steel - Furnish stressing steel according to one of the following as the
Contractor may elect, unless otherwise shown or specified:
Seven- Wire Strand ................................................................................ 02515.10 High Strength Steel Bars ....................................................................... 02515.30 Seven-wire strand epoxy coated reinforcement .................................... 02515.40
00555.12Tendon Grout - For grouting post -tensioning ducts, furnish a commercial, pre-packaged,
thixotropic tendon grout meeting the requirements of 02080.50. Label each grout bag with application, mixing and pumping instructions, lot number, date of manufacture and shelf life. A grout expiration date may be used in lieu of the date of manufacture and shelf life. Tendon grout will be rejected if the shelf life or expiration date has been exceeded.
Use water meeting the requirements of Section 02020.
At least 48 hours prior to the trial batch, submit a detailed written mix design showing the exact brand and batch quantities of pre-packaged grout and water including dosages proposed.
00555.13Tendon Grout Trial Batch - Mix a trial batch of grout using the Equipment , Materials,
proportions, and grouting crew proposed for use on the Project. Mix a trial batch of grout for each separate tendon grout lot number. If the duration between grouting stages is greater than 14 Calendar 00555.20 509 Days, a new trial batch is required. If the proposed grout mix design does not produce acceptable trial batch results, revise the mix design and perform another trial batch. Results from previous projects will not be considered acceptable documentation. Grouting may proceed any time after approval of the trial batch.
Perform the following tests:
as follows:
• Fill the flow cone to the top of the cone. • When thoroughly mixed, the efflux time of grout will be the time to fill a 1 Liter container that is placed directly under the flow cone. Ensure the efflux time of the grout immediat ely after mixing is between 5 and 30 seconds. • Let the grout stand for 30 minutes without agitation then retest as follows: • Remix for 30 seconds. • Ensure the efflux time of the grout immediately after remixing is within 10 seconds of the originally established flow.
Grouting of Post -Tensioned Structures M55.1" , modified as follows:
Vertical Rise, X Gelman Pressure Maximum % Bleed
0 ≤ X ≤ 20 50 0 X > 20 100 0
grouting operations according to API RP 13B -1 (American Petroleum Institute).
Sample 2 sets of 3 cubes at least once for each trial batch. Provide the test results to the Engineer for 7 and 28 -Day testing.
Equipment
00555.20Certified Calibrated Jacking Equipment - Equip each jack used to stress tendons with
either:
• A pressure gauge with an accurate reading dial at least 6 inches in diameter and of such capacity that the final pressure reading is in the upper half of its range. Calibrate each jack and its gauge as a unit with the cylinder extension in the approximate position that it will be at final jacking force, and provide a calibration chart certified by an independent testing agency; or • A certified, calibrated load cell with an indicator by which the stressing force in the tendon may be determined, and with a range such that the lower 10 percent of the manufacturer's rated capacity will not be used in determining the jacking stress.
Adjustment or repair of jacks, gauges, or load cell after certification will be cause for rejection. The calibration charts for the hydraulic jacks, pressure gauges or load cells used for tensioning stressing steel may be checked before and during tensioning operations by Agency personnel with Agency -furnished load cells. Perform certified ca libration of stressing system not more than 180 Days before use. 00555.21 510
00555.21Grouting Equipment - Provide grouting Equipment with:
• Separate motors or engines for the grout mixer and the grout pump, and a system for controlling each independent of the other. • A high speed, high shear, colloidal mechanical grout mixer that will produce uniform and thoroughly mixed tendon grout. • Equipment which will accurately measure solids and liquids to be batched. • An easily accessible filter screen before the grout pum p with clear openings of 1/8 inch maximum size. • A grout pump capable of producing a minimum pressure of 75 psi, with a pressure gauge reading from 0 to 300 psi, and with a relief valve that will limit grouting pressures to less than 200 psi. • Watertight grout hoses, valves and pipe fittings.
Provide standby water flushing Equipment which:
• Is in addition to and separate from the grouting Equipment • Has a different power source than the grouting Equipment • Is capable of developing a pumping pressure of 250 psi and has sufficient capacity to flush out any partially grouted ducts or vents if necessary
Labor
00555.30Personnel - Provide the following:
• Post-Tensioning Supervisor - A person, skilled in the use of the system of stressing to be used, to supervise the Work .
• Grouting Technician - An American Segmental Bridge Institute (ASBI) certified grouting technician or PTI Level 2 Bonded PT Field Specialist to supervise, inspect , and document the entire grouting operation.
Construction
00555.40Required Submittals :
size and type of anchorage device showing that the device meets the requirements of the AASHTO LRFD Bridge Design Specifications and the AASHTO LRFD Bridge Construction Specifications . With the certification, include a statement that the design, materials and manufacture of the anchorage devices have not changed si nce testing. Ensure the concrete strength, edge clearance dimensions and amount of reinforcing for the test block is not greater than that proposed for the Project.
for post -tensioning systems to the Engineer for review according to 00150.35.
and sequence proposed for the stressing operations, including, but not limited to:
• Additions or rearrangement of reinforcing steel or changes in member dimensions from that shown. 00555.42 511 • For normal anchorage devices, bearing stress and resistance calculations satisfying Section 5.10.9.7.2 in the LRFD Bridge Design Specifications. • Complete specifications and details of the ducts, stressing steel including arrangement and alignment, and the anchoring devices. • Pressure grouting Materials and Equipment . Furnish reinforcement Working Drawings that are compatible with the approved Post -Tensioning System Working Drawings .
Do not cast any member to be stressed before the Working Drawings have been reviewed according to 00150.35.
00555.41Ducts - Provide ducts for post-tensioning tendons according to the following:
directed. Provide positive, metallic, mortar -tight connection joints between sections of rigid duct which do not permit angle changes at the joints. Use waterproof tape at connections.
locations shown. Make vents of 3/4- inch nominal diameter standard PVC, gal vanized steel or copper pipe. Make connections to ducts with compatible structural fasteners. Make the vents mortar -tight, tape as necessary, and provide means for injecting grout through the vents and for sealing the vents. Securely fasten ducts and vents in place to prevent movement. After grouting, remove the ends of vents to provide 2 inches of cover to the nearest concrete surface.
than 1/4 inch may be repaired by several wraps of waterproof tape. Repair holes larger than 1/4 inch with a split metal sleeve which overlaps itself by 3 inches, extends at least 3 inches on either side of the hole, is sealed with waterproof tape, and is secured to the duct. C ut out indentations which cannot be repaired and repair as above for holes larger than 1/4 inch.
prevents entry of moisture or debris. If the surrounding temperature is below 32 °F, keep the ducts free of water to avoid damage due to freezing. Before placing forms for the decks of box girder cells, demonstrate to the satisfaction of the Engineer that all ducts are unobstructed.
Clean all ducts and remove accum ulated water at the time of placing stressing steel.
00555.42Stressing :
in the member after any stressing steel has been installed. Protect stressing ste el against physical damage and rust or other corrosion at all times until grouted. A corrosion inhibitor may be used. Stressing steel that has sustained physical damage, detrimental rust, pitting or other results of corrosion at any time will be rejected. Stressing steel with only light rust is acceptable if rust spots can be removed by rubbing or scraping with the fingernail and only light streaks of rust remain.
Tension stressing steel by means of hydraulic jacks so that the force in the stressing steel is not less than the value shown.
00555.43 512 (b) Duct Alignment - Provide a duct alignment according to the approved Working Drawings to the follow tolerances:
• Horizontal Alignment - ± 1/4 inch unless shown otherwise
• Vertical Alignment - ± 3/8 inch
temperature is below 40 °F for a total of 4 hours or more, after the last concrete has been placed in the member an d not until all the concrete has reached the specified compressive strength.
Subject to prior written approval, a portion of the total stressing force may be applied to a member when the concrete compressive strength in the member is less than the values hown. Approval of such partial stressing will in no way relieve the Contractor of full responsibility for successfully constructing the member.
noted.
stressing steel in each member from one end of the span and the other half from the opposite end, unless otherwise allowed in writing.
tensioned by jacking from one end only.
elongation of the stressing steel may be measured at any time. Keep a record of gauge pressures, load cell reading and elongations. Furnish a copy of the record to the Engineer when requested.
Determine prestressing force by both of the following methods:
load-elongation curves for prestressing strand used.
or by use of a calibrated dynamometer.
Ascertain the cause of any difference in force determination between (1) and (2) that exceeds 5 percent and correct the condition causing the discrepancy.
elements immediately after tensioning is complete. Search for cracking, distress, or other abnormalities and report findings to the Engineer. Obtain Engineer approval of the post -stressing survey before cutting strand ends.
00555.43Bonding and Grouting - Bond stressing steel to the concrete by filling the void space
between the duct and the tendon with tendon grout consistent with the approved trial batch. Complete grouting each tendon within 14 Calendar Days after placing it. If Project is within 25 aerial miles of the Pacific Ocean, complete grouting each tendon within 7 Calendar Days after placing it. Test grout according to ASTM C939, as modified in 00555.13(a) at the start of grout production, at least every 2 hours after the start of grout production, and as requested by the Engineer, to verify that flow characteristics of the grout remain within the tolerances specified in 00555.13(a). Perform Mud 00555.43 513 Balance tests for each batch according to 00555.13(c) . Compare and document the wet density value with the value obtained during the trial batch. If the values differ by more than 3 percent, rerun ASTM C939 as modified in 00555.13(a) for continued compliance.
Perform compressive strength tests according t o 00555.13(d) at least once daily and provide the test results to the Engineer for 7 and 28-Day testing.
Perform bleed resistance tests at the mixer location according to 00555.13(b) at least once daily.
stressing operations.
accessible and operable should it become necessary to flush out a partially grouted tendon.
Do not retemper grout. Continuously agitate grout until it is pumped.
duct thoroughly with oil -free air immediately before grouting. Ducts may be flushed with water immediately before grouting if approved. Fit grout injection pipes with positive mechanical shutoff valves. Fit vent and ejection pipes with grout -tight caps, valves or other mechanical closing devices.
Grout from the low end of the Structure .
Keep the temperature of the concrete surrounding the duct at 35 °F or higher at the time of grouting and until job -cured grout cubes reach 800 psi compressive strength.
Maintain grout temperatures between 50 °F and 90 °F during mixing and pumping. If neces sary, cool the mixing water.
Open all vents when grouting starts. Allow grout to flow from the first vent until residual flushing water or entrapped air is removed, then close the vent. Close remaining vents in sequence in the same manner.
Pump thixotropic grouts with 75 psi pressure or less between outlets. Reduce the pumping pressure to 5 psi while passing intermediate outlets or approaching the end of the tendon. Maintain pressure at 5 psi for 15 seconds after each outlet is reached. Resume 75 psi pressure between intermediate outlets after an outlet is closed off. Allow effluent bleed at tendon end using 5 psi pressure. Whenever the grout pumping pressure exceeds 100 psi:
• Inject grout at any other vent which has been, or is ready to be, closed as long as a one-way flow of grout is maintained. If this procedure is used, fit the vent used for injection with a mechanical shutoff valve. • If the one -way flow of grout cannot be maintained, immediately flush the grout out of the duct with water. Pump grout through the duct and continuously waste it at the outlet vent until:
• No visible slugs of water or air are ejected. 00555.80 514 • The afflux time of the grout at the mixer during the grouting process is not more than 5 seconds different from the efflux time at the mixer during the initial measurements of the flow cone test during the trial batch, and is between 5 and 30 seconds. • The efflux time of the ejected grout is not more than 5 seconds different from the efflux time at the mixer. Do not over -mix the g rout. Close the outlet vent and maintain the pumping pressure or 60 psi, whichever is greater, for at least 30 seconds; then close the valve at the injection pipe while maintaining this pressure. Do not open valves or vents until the grout sets.
tensioning blockouts with concrete and finish flush. Prepare post tensioning blockouts according to 00540.43(a) or as approved. Apply an epoxy bonding agent from the QPL to exposed bearing plate and wedge plate surfaces prior to placing concrete in the blockouts.
Measurement
00555.80Measurement - No measurement of quantities will be made for Work performed under this
Section. Estimated quantities of Materials will be listed in t he Special Provisions.
Payment
00555.90Payment - The accepted quantities of Work performed under this Section will be paid for
at the Contract lump sum amount for the item "Post -Tensioning". Payment will be payment in full for furnishing and placing all Materials, and for furnishing all Equipment , labor, and Incidentals necessary to complete the Work as specified.
No separate or additional payment will be made for anchorage devices, ducts, tendons, prestressing steel, grout, and admixtures, or for preparation and testing of grout.