865Manufacture of Prestressed Concrete Bridge Members

Bridge Members

865.1General Description

This section includes the following requirements for precast-prestressed concrete bridge members and piling: • Manufacturing • Inspecting • Testing • Marking • Painting • Rubbing as specified • Plant handling • Storing • Shipping The term “precast-prestressed concrete” is referred to as “prestressed concrete” in the rest of this Section. 865.1.01 Related References

AASHTO M 55 AASHTO M 85 AASHTO M 221 AASHTO T 22 AASHTO T 27 ASTM A 123/A 123M) 1644 1644 1644

ASTM A 153/A 153M) ASTM A 185 ASTM A 416 ASTM A 497 AASHTO Specification for Highway Bridges Laboratory SOP-3, Standard Operating Procedures for Precast/Prestressed Concrete QPL 9 GDT 35

865.2Materials

Use materials that meet the specifications as follows: Material Section Concrete, Class AAA (except as noted) 500 Steel Bars for Reinforcement 853.2.01 Pretensioning Steel Wire Strand 853.2.02 Post-Tensioning Steel Wire 853.2.03 Post-Tensioning Steel Bars 853.2.04 Plain Steel Bars—Threaded Ends 853.2.05 Portland Cement 830.2.01 Fine Aggregate for Mortar 801.2.02 Aluminum Powder 835.2.01 Self-Lubricating Bronze Bearing and Expansion Plates and Bushings 857.2.03 Primer Coats 870 Elastomeric Pads 885.2.01 Epoxy Resin Adhesive 886 Microsilica (Silica Fume) 831.2.03 NOTE: Do not use accelerators (24-hour accelerated strength concrete) that contain chlorides in any prestressed concrete. 1645 1645 1645

865.2.01 Prestressed Concrete Bridge Members

Portland Cement Use Type I, Type II, or Type III cement that meets requirements of AASHTO M 85 for low alkali cement.

Coarse Aggregate

that has direct contact with water. Microsilica (Silica Fume) The Department may approve silica fume as an additive to concrete. If approved, add the silica fume at a rate not to exceed 10 percent of the cement content. Epoxy-coated Reinforcement Steel and Wire: If top steel mat of the bridge deck is epoxy-coated, the shear steel in the prestressed concrete beams will be epoxy-coated in accordance with Section 514. Welded Wire Fabric Use welded wire fabric that meets the following requirements:

Section.

Pretensioning Steel Wire Strand Use strands that meet all the requirements of ASTM A 416, Grade 270. Slump Limitation Ensure the slump meets Subsection 500.1.03.A Table 1 – Concrete Mix Table , except when Type F high range water reducers (HRWR) are added. With HRWR, you may increase the slump value from 4 in. to 6 in. (100 mm to 150 mm) with a maximum slump value not to exceed 7 in. (175 mm), provided the concrete mix does not segregate. Facilities and Equipment Plans Facilities are approved according to Laboratory SOP-3, Standard Operating Procedures for Precast/Prestressed Concrete. See QPL 9 for a list of approved facilities. Submit a complete set of plans and an itemized equipment list of the prestressing facilities to the Engineer.

about approval. The plant need not comply with the requirements concerning plans and equipment listing.

production methods, types of products, or for any other reason. 1646 1646 1646

General Plant Requirements Furnish erection drawings to the Engineer that show the placement of superstructure units, especially when the units are not interchangeable with respect to transverse placement within a span or with respect to the reversal of ends within a span. Manufacturing Facilities and Equipment Ensure that the prestressed concrete bridge members are made at a plant that has as a minimum the facilities and equipment specified as follows:

NOTE: Regardless of approval, the Contractor is responsible for the facilities’ performance and obtaining additional equipment as needed.

acceptable to the Engineer.

design load.

1) Design the forms so the bridge members will be well within the tolerances specified in Subsection 865.2.01.B.11. 2) Anchor the forms to prevent movement.

1) Jacks: Use jacks in good repair that do not leak. Calibrate them with the actual gauge or gauges that you will be using. You may use pressure gauges, load cells, or dynamometers. Ensure all jack systems have devices that prevent the gauge pointer from fluctuating. 2) Calibration: Calibrate all devices to a reading accuracy of 2 percent within the proposed stressing range. Use an approved testing laboratory to calibrate the devices. Have the laboratory furnish at least five copies of the calibration chart for each device to the Engineer. Recalibrate all stressing systems at least every 6 months and as required by the Engineer. Use gauges that you can read from 6 ft. (1.8 m) and have a capacity of twice the maximum load.

bed or anchorages.

on prestressed concrete units unless the Engineer gives written permission. 1) Water Curing: Use equipment that consists of a clean, non-deleterious water source, a method of application, and enough burlap or other means of moisture retention that will keep all surfaces of the concrete wet during the curing cycle, except those in contact with the forms. 2) Steam Curing: Use the following minimum basic equipment: • An enclosure tight enough to maintain a uniform atmospheric temperature around the concrete units. • A steam system that distributes live steam uniformly through nozzles, capable of maintaining a temperature of at least 120 ºF (50 ºC) in all weather. Do not eject steam directly against concrete or forms. • A controlling device installed in the steam line that helps maintain a constant temperature. • A recording thermometer for each 200 ft. (60 m) of bed length. 1647 1647 1647

3) Heated Forms: Uniformly heat the forms with a recirculating system that distributes the heat evenly. Use a system that includes: • A means of retaining moisture on concrete surfaces, except those in contact with the forms. • A recording thermometer for each 200 ft. (60 m) of bed length. • A weathertight covering for each bed to ensure uniform heating throughout the bed.

small enough to reach through the prestressing and reinforcing steel to all portions of the form. 1) Use enough vibrators to properly compact the concrete. Have an additional stand-by vibrator in good operating condition for each concrete placing operation. 2) Get the Engineer’s approval of the vibration procedure and of the number and types of vibrators before pouring. 3) You may use external vibration in conjunction with internal vibration when the Engineer so approves.

lbs./in.² (520 kPa) for at least 15 seconds.

concrete bridge members without settlement. Ensure the storage area has blocks to support the units properly at the required points. Substitution of Reinforcement You may substitute welded wire fabric for the bar reinforcement shown on the plans. The Department will not pay extra for the substitution. The substitution is subject to the following:

for approval before using welded wire fabric.

provided by the bar reinforcing shown on the plans.

drawings on 22 x 36-in. (550 x 990 mm) sheets.

40,000 psi (275 MPa). Do not splice by welding or mechanical coupling.

the beam at least 6 in. (150 mm) into the slab. Leave at most a clearance of 4 in. (100 mm) from the top of slab to the welded wire fabric.

closer cross wire clearing the top of the beam by at least 2 in. (50 mm).

that enclose the prestressing steel in the bottom flange, and the vertical stirrups that do not protrude beyond the top of the beam.

of the bar reinforcing.

Bridges for the proper methods to embed and splice the fabric. 1648 1648 1648

Substitution of Strands You may use strands of different arrangement, size, or arrangement and size. The Department will not pay extra for the substitution. The substitution is subject to the following structural and physical requirements:

Specification for Highway Bridges.

the plans.

notes. Ensure that the design notes indicate compliance with the requirements. Prepare drawings on

22 x 36-in. (550 x 900 mm) sheets.

NOTE: If you propose to use strands that differ in size from those covered in ASTM A 416, submit

complete data on the strands to the Engineer for approval.

Do not use individual strand couplings.

Concrete Manufacture and Mixing

HRWR.

1) When adding HRWR, dose the HRWR at the casting yard under the direct supervision of the

producer’s Quality Control. Do not exceed the HRWR manufacturer’s recommended dosage.

2) After dosing, mix the concrete at mixing speed for at least 70 revolutions.

NOTE: Do not exceed 360 total revolutions at mixing and agitating speeds.

3) After adding the plasticizer, no additional mixing water will be permitted.

Concrete Pouring

Fabricate the ends of all beams and girders to be vertical in the final erected position,.

the member.

Methods of Prestressing

You may either pretension, post-tension, or combine these methods to prestress concrete bridge members.

NOTE: Do not use strands from more than one source in any one tensioning operation. 164916491649

Ensure the method used meets these requirements:

1) Strand Splices: Get approval from the Engineer for splicing methods and devices.

Jacking Method Action

Single-strand Use only one splice per strand.

Multi-strand Splice all strands or no more than 10% of the strands.

Ensure that the spliced strands have similar physical properties, are from the same source, and have

the same “twist” or “lay.” Locate splices outside the prestressed units.

2) Wire Failures: The Engineer may accept wire failures if the area of broken wires does not exceed 2

percent of the total area of the strands.

3) Stressing Preparations: Prepare the members as follows:

contaminated, clean the strand with a suitable solvent or replace the strand.

865.2.01.B.11.

release of stress. Ensure that the vise grips seat no more than 1/4 in. (6 mm) each.

pressure exerted by the concrete.

diameter of the strand plus 1/8 in. (3 mm).

location shown on the plans, ± 1 in. (25 mm).

material compatible with both the concrete and steel. Do not debond the strand for the full length

of members.

4) Pretensioning Operation: Use elongation to control this operation. Ensure that the hydraulic pressure

gauge readings at the time of the measured net elongation are within 5 percent of the calculated

gauge reading for that particular elongation.

Ensure that the net elongation and final gauge measurements agree within ± 5 percent of their

computed theoretical values.

The measurements of force and elongation shall algebraically agree with each other within a 5%

tolerance.

If any measurement varies by more than 5 percent, the Department will stop all work. Correct the

defect before proceeding.

Pretension the members as follows:

strand.

Do not use elongation to measure the amount of initial tension, but use a dynamometer, hydraulic

jack gauge, or dead weight. 165016501650

reference points. Use points that are independent of any movement in the bed or anchorages

that might occur during the pretensioning operation.

Calculate the design elongation as follows:

D = Design elongation in inches (millimeters).

P = Tensioning force, in pounds (kilonewtons); subtract the initial tensioning force from P.

L = Distance from dead end anchorage to reference point, measured in inches (millimeters)

A = Cross-sectional area of strand, in square inches (millimeters).

E = Modulus of elasticity of strand, in pounds per square inch (MPa).

Correct any movement in the anchorage abutments or in the overall anchorage system. Use the

final elongation figure as the net elongation in jacking the strand.

any strand.

Raise or lower the strands to their final position to get the final tension.

Ensure that the strands have no more than four points where the strand changes slope, two of

which shall be at each anchorage.

Use approved, low friction devices at pick-up and hold-down points. Make the devices maintain

the desired vertical and horizontal positioning of the strand.

After partial jacking, deflect the strands to their final position in a sequence approved by the

Engineer.

Subsection 865.2.01.B.11.

Uniformly distribute stress in the strands throughout the bed length.

5) Detensioning Operation: Before detensioning, submit the pattern and schedule for releasing the

strands to the Engineer for advance approval.

Detension the members as follows:

to releasing the stress.

temperature and shrinkage changes. Where possible, release the pretensioned strand while the

units are moist and warm.

or members after curing with steam.

6) Stress Release Strength: You may transfer stress to the concrete, unless otherwise specified on the

plans or in the Special Provisions, based on the following requirements (minimum strength

determined by cylinders cast of the same concrete):

D = PL

AE where 165116511651

Section Minimum Strength Age

Concrete I-beams, box beams, flat slab deck sections, or tee

slab deck sections

4500psi (30 MPa) 18 hrs

Piling 4000 psi (28 MPa)

Other members As specified on the plans

7) Strand Release: Use the following table for each type of strand:

Type of Strand Release

Single strand Heat each strand and allow it to pull itself apart in the sequence of the approved

pattern and schedule of release.

Do not cut the strands.

Multiple strand Release either a symmetrical group of strands or all of the strands simultaneously.

Remove the load on the strands from the anchorage and place it on the jacking

system.

Gradually release the jack or jacks until the strands are relaxed.

Draped strand Release according to a method where the weight of the beam is compared with

twice the total amount of the vertical components of the hold-down forces.*

*Use one of the following two methods:

Method Release as follows:

Method I (beam weight less than

twice the total amount and vertical

restraints cannot counteract the

vertical components of the hold-

down forces)

Heat each draped strand at the end of each member to failure in the

sequence of the approved pattern and schedule of release.

Release hold-downs and remove hold-down bolts.

Release straight strands as noted in Subsection 865.2.01.B.7.a.(7)

Method II (beam weight more than

twice the total amount)

Release hold-down devices within the beam.

Release the strands from the top to the bottom by either heating or jacking in

the sequence of the approved pattern and schedule of release.

systems may include the post-tensioning of both straight and draped tendons. Ensure that the system

meets the appropriate requirements that follow:

1) Tendons: Do not splice post-tensioning tendons.

2) Ducts: Accurately position the ducts in which post-tensioning tendons are placed and securely fasten

them to prevent movement during concrete placement. Use flexible metal conduit, metal tubing, or

other acceptable material for the ducts.

3) Stressing Requirements: Prepare the members as follows:

contaminated, clean the strand with a suitable solvent or replace the strand.

165216521652

4) Concrete Strength: Stress the post-tensioning tendons after the concrete in the member has reached

the minimum strength and age requirements, as follows:

Minimum Strength Age

4500 psi (30 MPa) 3 days

4000 psi (28 MPa) 5 days

draped tendons from each end.

Pretension the members as follows:

1) Initial Tension: After threading the tendon in the duct, apply an initial tensioning force of up to 5

percent of the final tensioning force with a jack.

Determine the initial tension by reading the gauge. Do not use elongation to measure the amount of

initial tension.

2) Final Tension: Compute the final stress on tendons from the amount of the final elongation

measurement, checked by the jack pressure gauge reading.

3) Gauge Reading: Ensure that the pressure gauge reading at the time of the measured elongation is

within 5 percent of the calculated gauge reading for that particular elongation.

If the gauge pressure reading varies by more than 5 percent from the calculated reading, stop the

stressing operation and correct the defect before proceeding.

4) Jacking: While jacking draped tendons, ensure that jack pressures and elongations are kept as near

equal as is possible at each of the two jacks so the elongation measurements and jack pressures

remain proportional.

5) Anchor Devices: Design anchor devices that secure the tendon for the size of post-tensioning tendon

used.

After anchoring, ensure that the devices can maintain a prestressed load of 150 percent of the

maximum design load and do not slip more than 1/8 in (3 mm) after anchoring.

Place anchor devices exactly at right angles to the axes of the post-tensioned tendons. Carefully note

anchorage losses and take the proper corrective measures to ensure that the tendon has the final

design stress. 165316531653

Grouting

1) Mix, by volume, 1 part Portland cement, 0.75 part (max.) sand passing a No. 30 (600 μm) sieve, and

0.75 part (max.) water.

2) Within the limit specified, vary the proportions of sand and water as required by the Engineer.

3) If you need to fill enclosures as hereinafter specified, you may eliminate sand and use a neat cement

grout in the mix.

4) After adding all ingredients, mix the batch for three minutes.

5) Make batches of grout small enough so that the batch may all be used up in less than 45 minutes.

6) Immediately before grouting, blow out tendon ducts with compressed air. Ensure that the

compressed air does not contain oil.

7) Vent each duct at each end. Ensure the vent has the means for positive closure when subjected to a

minimum pressure of 75 psi (515 kPa).

8) Pump the grout into the duct towards an exit vent.

9) After the grout has expelled all entrapped air and is flowing in a solid stream, close the exit vent and

build the pumping pressure to a minimum of 75 psi (515 kPa). Hold it at that level for a minimum of 15

seconds.

10) Close the grout entrance vent.

11) Do not move or disturb the member at all for at least 48 hours after grouting.

Concrete Finish

1) Finish the outside face of certain exterior beams specified in the Table of Bridge Areas Requiring a

Type III Finish in Subsection 500.3.05.AB with the Type III Special Surface Coating Finish.

2) Finish all other beams with a steel form finish.

3) Score the surfaces of the top flanges of all beams with a stiff wire brush or equivalent. Score the

beams transverse to the longitudinal axis of the beams.

4) Transversely scrub the entire beam top with a coarse brush to remove all laitance and to produce a

roughened surface for bonding to the slab. Remove all concrete fins or projections to produce a

vertical face at the edge of the beam.

5) If using prestressed concrete deck panels, finish both sides of the beam’s top flange with a trowel for

2 in. (50 mm) from each panel edge to ensure a smooth and level bearing area.

double tees, etc.—as specified in Subsection 500.3.05.T.9 and the plans.

Finish the traffic face and top face of curbs on exterior units and the outside face of certain exterior

beams as specified in the Table of Bridge Areas Requiring a Type III Finish in Subsection 500.3.05.AB.

specified in Subsection 500.3.05.AB.5.

with extensive honeycombs within bearing areas.

1) Patch as directed by the Engineer, as soon as possible after form stripping.

2) The Engineer may require that you use an epoxy bonding compound.

3) Remove hold-down devices from the bottoms of the beams.

4) Coat the resulting holes with an epoxy bonding compound and plug them with grout. 165416541654

Concrete Curing

Cure concrete with one of the methods listed below. Provide means for keeping the temperature of bridge

members above the freezing point for 6 days after concrete placement, except for steam curing. The

Department may reject bridge members based on improper curing.

suitable material.

Keep the member wet for 7 days or until the concrete has reached the stress release strength specified in

Subsection 865.2.01.B.7.a.(6).

1) The Engineer may delay the start longer if the concrete has not taken its initial set. You may use

sufficient heat during the delay to maintain the temperature of the concrete between 50 º and 70 ºF (

10 º and 21 ºC).

2) Ensure the steam curing enclosures retain moisture and heat.

3) After steaming begins, you may raise the enclosure temperature at a maximum rate of 80 ºF (27 ºC)

per hour until the surface temperature of the concrete reaches an optimum temperature, not to

exceed 190 ºF (88 ºC).

4) Ensure that the differential surface temperature of the concrete within a member does not exceed 40

ºF (4 ºC) during the curing period.

5) Continue steaming until reaching the stress release strength.

6) Lower the enclosure temperature at a maximum rate of 40 ºF (4 ºC) per hour.

7) Maintain a film of water on all exposed surfaces of the concrete during the steam curing cycle.

8) Do not exceed the maximum temperatures.

9) The Department may reject bridge members based on excessive temperature.

times.

1) Enclose the beds with a suitable weather-tight covering supported to uniformly heat throughout the

bed.

2) Apply the requirements stated in Subsection 865.2.01.B.10.b concerning the delay period,

temperature control, curing duration, and basis of rejection.

Tolerances

Standard Operating Procedures for Precast/Prestressed Concrete. These tolerances generally will be the

maximum deviation allowed, although normal manufacturing tolerances will be well within those listed.

Galvanized Coatings

components and all exposed surfaces of attached structural steel bearing components according to

ASTM A 123/ A 123M or A 153/ A 153M.

cleaned.

or jobsite. 165516551655

Marking

NOTE: This requirement does not apply to single point pick-up locations placed on piling.

and accuracy of all markings on bridge members according to these specifications.

personnel to ensure that the work is properly done with respect to time of marking, accuracy of

description, and accuracy of location of marks and lettering.

Department to the Inspector at the plant, nor until the Inspector checks and approves the markings

required by these specifications.

manufacture, beam identification number (properly located to coordinate with the erection drawing), pile

length, and location of pile single-point pick up.

1) Before Stress Transfer: Immediately after forms are removed and before transferring stress,

individually identify and date members. This helps keep accurate records on each member’s bed

location and date of concrete placement.

2) Before Shipping: Give the Inspector advance notice of shipping. After securing members for

shipment, apply marking consisting of the Project identification to each member.

stamp until after the members have been satisfactorily finished and stored.

Handling and Storing

action and excessive rusting.

1) The Department will not consider light rust that does not visibly etch the steel as detrimental.

2) Keep prestressing steel free of harmful materials, such as grease, oil, wax, clay, dirt, paint, and loose

rust.

3) Use special care to keep prestressing steel free of form oil and other bond-reducing material that may

be used on the forms.

4) Handle prestressing steel at all times in such manner as to prevent kinks and nicks. The Department

will not allow prestressing tendons that have kinks, nicks, bends, or other defects.

5) Do not use torches or welding equipment adjacent to tensioned strand unless the strand is insulated

against heating or burning.

Section 511.

a way to eliminate the danger of cracks, fractures, and excessive bending stresses. Handle members by

the two embedded pick-up points, unless the Engineer approves other methods.

1) Except for piling, handle members so their vertical axes remain plumb at all times.

2) Support members in storage on firm blocking located immediately below the two embedded pick up

points. In multiple layer storage, support members in the stack with blocks of uniform thicknesses

and in a vertical line.

3) Set all blocking at right angles to the longitudinal axis of the member, and the longitudinal axis of the

blocking shall be horizontal. Do not ship members until the concrete reaches its ultimate design

strength. 165616561656

NOTE: Replace members that were damaged in handling or storage at no additional expense to the

Department. However, the Engineer may determine that the damage is minor and may approve use of

the member.

1) The Department may reject any piling cracked in handling, storing, or loading if the crack warrants.

2) The Department will reject any cracked piling destined for locations involving sea water or alkali soils.

3) Mark rejected pile as rejected.

4) Store piling in groups with the same length.

5) Transport piling in a manner approved by the Engineer. Upon request, the Engineer will furnish

drawings giving the limits of truck bolster spacing for various sizes and lengths of piling.

1) Use pick-up and support points within 3 ft. (900 mm) of the beam ends.

2) Support beams on firm blocking located within 3 ft. (900 mm) of the permanent bearing area of the

beam.

3) You may handle or store fully post-tensioned beams 48 hours after the grout has been placed in the

tendon ducts.

4) For beams manufactured by the combined method of pretensioning and post-tensioning, you may

handle and store them after the pretensioning phase is completed. Do not handle again until 48 hours

after grout placement.

5) Do not ship beams and other superstructure units until after their strength reaches the required

minimum 28-day design strength.

6) Store beams in single layers, not in stacks. Support beams so they meet the following requirements

concerning warp and sweep:

Twist of vertical axes of the ends of beams due to

misalignment of blocking

The maximum deviation between the vertical axes of the

ends of beams shall be 1/4 in./ft. (20 mm/m) of beam

height.

Tilt of vertical axis of an end of beam from the

vertical due to deviation of blocking from the

horizontal

The maximum deviation of the vertical axis of an end of a

beam shall be 1/4 in./ft. (20 mm/m) of beam height.

Lateral sweep due to manner of storage There shall be no discernible sweep induced by the

manner in which a beam is stored.

Plant Inspection

inspect all plant facilities involved in the production. Do not manufacture anything until the Engineer

approves all facilities.

production process.

the specifications. In cases of dispute, the Contractor may appeal to the Engineer, whose decision will be

final. 165716571657

Rejections

If any material or finished members are defective, they will be rejected, even though the Inspector may have

accepted them.

Provisions for Testing

Furnish and maintain sufficient testing equipment so that the Inspector can conduct the following tests at the

casting yard:

Material Test Method

Fine Aggregate AASHTO T 27

Coarse Aggregate AASHTO T 27

Hardened Concrete GDT 35

capping compound, sufficient to test compression specimens according to AASHTO T 22.

use. The Department will not compensate the Contractor if the work is delayed waiting for approval of the

materials furnished for testing.

Facilities for the Inspector: Furnish for the sole use of the Inspector a suitable field laboratory according to

Subsection 106.04, Subsection 106.11, and Subsection 152.

General Provisions 101 through 150.. 1658 1658 1658