SECTION 604
PRESTRESSED CONCRETE BEAMS
604.01 GENERAL
This work consists of furnishing required materials and fabricating, transporting, erecting,
finishing, and adjusting prestressed concrete beams.
604.02 EQUIPMENT
Use a plant and equipment as specified in Section 157 “Concrete Equipment.” The Engineer
may grant written permission to use other types of concrete mixers.
604.03 MATERIALS
A. General
Item
Concrete
Grade 60 Concrete Reinforcement
Wire, Strands, and Anchorage Assemblies
Section
802
836
836.03 E
Perform tests to determine the concrete’s compressive strength using 6 inch by 12 inch
cylinders.
Use the same brand and grade of cement and admixture for all beams in any one bridge
structure.
B. Concrete Mix Design
1. General
Develop a mix design that produces concrete that will achieve a minimum compressive
strength of 5,000 psi within 28 days.
If using air-entraining cement or admixtures, maintain the air content between 4 percent and
7 percent.
Obtain the Engineer’s approval for all other admixtures before developing the mix design.
Include any admixtures in the mix design.
2. Trial Mix
Produce a trial mix using the mix design in the presence of the Engineer.
Cast, cure, and test a minimum of ten cylinders under the supervision of the Engineer.
Cure the cylinders for the same length of time and under identical conditions that the beams
will be cured under. Test four cylinders at 14 days and the remaining six at 28 days.
Submit the test results with the mix design to the Engineer for approval at least 14 days
before casting the beams.
3. Mix Design Revisions
If any material or material source changes, develop and submit a revised mix design as
specified in Section 604.02 B “Concrete Mix Design.”
B. Wire, Strand, and Bars
Assign lot numbers to all wire, strands, and bars and tag them for identification.
C. Inspection
Notify the Engineer a minimum of two weeks before manufacturing the beams.
Allow the Engineer free entry to all parts of the work involving the manufacture of the
beams.
D. Sampling and Testing During Manufacturing the Beams
1. Concrete
Cast cylinders in a sequence so all concrete used in the beams is represented by tests.
If casting a single beam, cast and test a minimum of five cylinders. Test 2 cylinders to
determine concrete compressive strength at the time of stress transfer. Test 3 cylinders
on or before the 28 day test period to determine the compressive strength for delivery
and the Engineer’s acceptance.
If casting two or more beams during one continuous operation, cast and test a minimum
of six test cylinders:
 3 cylinders per bed, to be tested at the time of stress transfer, that include:
 1 cylinder representing the first beam cast;
 1 cylinder representing a beam near the center of the bed; and
 1 cylinder from the last beam cast.
 3 cylinders for determining compressive strength to make delivery and obtaining
acceptance by the Engineer on or before the standard 28 day test period.
2. Wire, Strand, and Bars
Submit a certified mill test report and a certificate of compliance for reinforcing installed
in beams. Include the diameters, elongation at rupture, and ultimate tensile strengths in
the mill report.
E. Acceptance
Deliver the beams after the minimum compressive strength requirements are obtained.
The Engineer will reject beams not meeting the minimum compressive strength
requirements at 28 days.
Furnish a certified statement, signed by the Engineer, showing the number of beams cast in
each continuous operation and the number of each beam.
F. Waivers
If the beam fabricators plant meets the requirements of the Department’s Quality Assurance
procedures, the Department will waive the sampling, testing, and inspection requirements
specified in Sections 604.02 A “General,” 604.02 C “Inspection,” and 604.02 D “Sampling
and Testing During Manufacturing the Beams” and substitute the following:

Furnish a certificate of compliance that also includes the source of the materials
used in manufacturing.

Furnish the required certificate for the wire, strand, and reinforcing. Furnish a
certificate analysis of the aggregates and stating that the aggregates have been
tested and approved.

At the time of stress transfer, test two concrete test cylinders for a single beam pour,
and three concrete test cylinders for a continuous pour representing the beams as
provided for in Section 604.02 D.1 “Concrete.”
604.04 CONSTRUCTION REQUIREMENTS.
A. General
Determine the prestress force applied to the strands by strand elongation, and check by
calibrated hydraulic jacks. Furnish a certified statement of curve giving the load elongation
relationship at 75 percent (low relaxation strand) of ultimate stress for the prestress steel to
be used. Furnish a certified calibration curve for each hydraulic jack.
B. Shop Drawings
Ensure shop drawings show:
- Beam dimensions;
- Size and location of all reinforcing and prestressing steel;
- Details of end anchorages, if used; and
- Any necessary revisions to bridge seats.
Submit calculations and work drawings that are signed, sealed, and dated by a Professional
Engineer registered in the State of North Dakota as set forth in NDCC Title 43.
C. Placing and Fastening Steel
Place steel as specified in Section 612.04 “Construction Requirements” and as follows:
Maintain distances between the forms and steel reinforcing using stays, ties, hangers, or
other approved supports. Ensure metal bar chairs and bolsters in contact with the forms are
galvanized or noncorrosive metal. Do not leave wooden blocks in the concrete.
Straighten prestressing elements by applying low initial tension to insure proper positioning.
Include this initial tension in the total tension applied. If required, provide suitable horizontal
and vertical spacers to hold elements in true position.
D. Placing Concrete
Measure, mix, handle, and place concrete as specified in Sections 602.04 C “Mixing” and
602.04 D “Placing Concrete” using concrete as specified in Section 802 “Portland Cement
Concrete.”
Vibrate concrete for the beams. Vibrate without displacement of reinforcing, conduits, voids,
or wire. Vibrate for a sufficient duration and intensity to thoroughly consolidate the concrete
without causing segregation.
E. Curing Concrete
Steam or water cure members until the concrete has reached the compressive strength
required for stress transfer. Protect members from rain, cold weather, and moisture loss
between placement of the concrete and the beginning of the steam or water cure.
Cover all exposed surfaces with two layers of burlap as soon the covering is able to be
placed without damaging the concrete.
Maintain a uniform curing temperature.
1. Steam Cure
Cover steam cured members with a suitable covering to contain the live steam. Distribute
the steam uniformly throughout the enclosure and do not jet the steam directly on the beam.
Maintain the temperature of the enclosure below 90°F until the beam has cured for a
minimum of three hours. After this period the Engineer will allow the temperature within the
beam enclosure to be raised to a maximum of 160°F in increments less than 40°F per hour.
2. Water Cure
Apply water to the burlap cover so that the concrete surfaces are kept continuously wet.
F. Pretensioned Beams
Accurately hold prestressing tendons in position and stress the tendons with jacks. Submit a
record of the jacking force and the elongation produced.
Do not allow bond stress to be transferred to the concrete and do not release end
anchorages until the concrete has reached the compressive strength required for stress
transfer.
Cut tendons only after heating them to relieve the stress. Cut tendons so the lateral
eccentricity of prestress force is minimized.
G. Transportation and Storage
Transport precast beams in an upright position, and ensure the points of support and
directions of the reactions with respect to the beam are approximately the same during
transportation and storage as when the beam is in its final position.
604.05 METHOD OF MEASUREMENT
The Engineer will measure as specified in Section 109.01 “Measurement of Quantities.”
604.06 BASIS OF PAYMENT
Pay Item
Prestressed Beams
Pay Unit
Linear Foot
Such payment is full compensation for furnishing all materials, equipment, labor, and incidentals
to complete the work as specified.