- 498 - SECTION 705 -- PRECAST OR PRECAST/PRESTRESSED CONCRETE STRUCTURAL UNITS
705.01 Description
1.This work consists of all labor, materials, and equip ment required in the production of Precast or Prec ast/Prestressed Structural Units.
2.The contract shall be supplemented by Contractor-provided working drawings submitted in accordance with Subsection 105.02.
705.02 Material Requirements
1.The materials used shall meet the requirements described in Table 705.01. Table 705.01 Material Requirements Applicable Material Section Concrete .......................................... .1002 Admixtures ....................................... .1007 Water 1005 Fine Aggreg ate ................................ .1033 Course Aggr egate ............................ .1033 Fly Ash 1008 Spiral Reinforc ing Wire .................... .1023 Prestressed Steel Strand ................. .1026 Post-Tensioning Assembly Steel ..... .1025
2.The concrete class used in the manufacture of Precast or Precast/Prestressed Structural Units shall be shown in the contract.
3.The Contractor shall be responsible for the concrete mix design. Concrete mix designs shall be proportioned in accordance with ACI Standard 318 and the following additional requirements:
a.The mix designs or change to a mix design shall be submitted for approval to the Engineer 4 weeks before beginning any concrete work. Refer to Table 705.03 for required testing for any mix design.
b.Concrete shall consist of Type I, Type II, or Type III Portland cement, aggregate, air-entraining admixture, and water. Concrete may also contain Class C or Class F fly ash, slag cement or Silica Fume and ASTM C 494 approved Type A, Type B, Type D, and Type F admixtures.
c.No change shall be made in the approved concrete mix design during the progress of the work without the prior written permission of the Engineer.
4.Reinforcement shall be furnis hed, handled, stored, and placed in accordance with the requirements of Section 707.
5.Welding of reinforcing steel is prohibited unless specifically authorized by the Engineer.
6.Prestressing steel other than t hat specified in the contract may be furnished with the approval of the Engineer. The yield and ultimate strength and other pertinent characteristics of this steel shall be submitted to the Engineer. Precast or Precast/Prestressed Concrete Structural Units 705.02 - 499 - 7. The area of broken wires shall not exceed 2% of the cross sectional area of the stressing strands when t he number of strands is 14 or less.
8.No more than 1 broken wire will be allowed in a single strand. 9. Bars for post-tensioning shall be of high tensile strength steel. They shall be equipped with wedge type e nd anchorages which will develop the minimum specified ultimate bar stress on the nominal bar area. The physical properties of the bar steel determined by static tensile tests shall conform to the requirements in Table 705.02. Table 705.02 High Strength Steel Post-Tensioning Requirements Ultimate Stress ...................... 145,0 00 psi (1000 MPa) minimum Stress at 0.7% Elongation ....... 130,000 psi (900 MPa) minimum Stress at 0.3% Elongation ......... 75,000 psi (500 MPa) minimum Elongation in 20 Diame ters .................................... 4% minimum Modulus of Elasticity ...... 25,000,000 psi (172,00 MPa) minimum Diameter Toler ance ................... Plus or Minus 0.1 inch (2.5 mm)
10.Materials specified for testing shall be furnished 30 days before the anticipated time of use. All materials required for testing shall be furnished by the Contractor to the Engineer wi thout additional costs to the Department. The Engineer shall select a represent ative sample length for the various prestressed steel as follows:
a.Six feet (1.8 m) for wires requiring heading.
b.For wires not requiring heading, sufficient length to make up one parallel-lay cable 6 feet (1.8 m) lo ng consisting of the same number of wires as the cable to be furnished.
c.Six feet (1.8 m) between near ends of fittings for a strand furnished with fittings.
d.Six feet between threads at the ends of bars furnished with threaded ends.
11.If the anchorage assemblies ar e not attached to prestress steel samples, 2 anchorage assemblies shall be furnished for testing, complete with distribution plates of each size or type of prestress steel to be used.
12.Any defective material shall be rejected. 13. Concrete quality control shall be the responsibility of the Contractor. Concrete shall be sampled and tested as shown in Table 705.03.
a.The Contractor’s test result s are the basis for acceptance. If the Department’s quality assurance te sting is not within 10% of the Contractor’s test results on any given sets of three cylinders, the Engineer will initiate an investigation to find the cause of the variation between the Contractor’s and the Department’s test re sults. While the investigation is in progress, the department will continue with quality assurance testing as shown in Table 705.03. Any structural un its represented by these tests will be subject to rejection.
705.02 Precast or Precast/Prestressed Concrete Structural Units
- 500 - b. If more than one set of cylinders is required per Table 705.03 for a single Precast or Precast/Prestressed Concrete Structural Unit, each set of three cylinders will be averaged separately. All averaged sets must meet the minimum design strengths.
c.If 40 cubic yards makes more than one Precast or Precast/Prestressed Concrete Structural Unit and the Contractor elects to make the minimum set of cylinders, that single set of cylinders will be used to determine the girder strength for all of the Precast or Precast/Prestressed Concrete Structural Units that set of cylinders represents. If the Contractor elects to make more than the minimum cylinders required, in order to represents each Precast or Precast/Pre stressed Concrete Structural Unit, only the set of cylinders representing the corresponding unit will be used to determine the strength of that unit. Precast or Precast/Prestressed Concrete Structural Units 705.02 - 501 - Table 705.03 Precast Plant Approval Plant Certification Contracto r Prestressed: Shall submit PCI Certification every two years to the PCC Engineer. Precast: Precast plants that are not PCI certified will be NRMCA certified. NDOT Approve and add to SiteManager. Quality Control & Quality Assurance at Plant Site Frequency Daily Weekly Number of Acceptance Cylinders to be fabricated Contracto r Quality Control - Will make a minimum of six cylinders for every 40 cubic yards. - NDOT personnel will record results and enter into SiteManager. These samples will be identified and tagged by NDOT. NDOT shall have access to these QC samples at all times. NDOT Personnel Quality Assurance - Will make a minimum of six sets of three cylinders per week of production. - The NDOT samples will be taken at the same location within a load of concrete as the contractor’s QC samples. NDOT shall choose the location of these samples within the load/girder. - Enter results into SiteManager. Required Testing for Acceptance Cylinders Contractor Laboratory : - 7 Day Compressive Strength: three cylinders averaged at contractor’s discretion. - 28 Day Compressive Strength: three cylinders averaged. - 56 Day Compressive Strength: The remaining three cylinders will be tested for 56 day compressive strengths; only if the 28 day compressive strength failed to meet specification requirements. Note: No cylinders are to be discarded until all design strengths are met and the prestressed unit(s) is accepted. - Air Content - ASTM C 231 - Slump Flow - ASTM C 1621 - Visual Stability Index (VSI) Appendix of ASTM C 1611 is required. NDOT Laboratory : - 28 Day Compressive Strength: Three cylinders averaged. ● The 28 day compressive strength is to be used for validation of the contractor’s strength. ● Note: If the Contractor’s and Department’s 28 day test results are not within 10%, the average set of three cylinders for 28 or 56 day will be used for acceptance. ● NDOT will be onsite to witness the testing for all Acceptance Cylinders. - Air content - ASTM C 231 - Witness Slump Flow & Visual Stability Index
705.02 Precast or Precast/Prestressed Concrete Structural Units
- 502 - Table 705.04 Mix Design Approval/Change Cement or Aggregate Source Refer to policy in the Material & Sampling Guide for the following: Frequency Weekly Required Inspection ● Precast/Prestressed Concrete Plant Inspection-NDOT Inspector ● Precast/Prestressed Concrete Plant Inspection-Fabricator Inspector Trail Mix Contracto r Data from 15 trial tests as a minimum (New Mix Design) Data from 5 trial tests as a minimum (Change in Cement or Aggregate) NDOT Contractor is responsible to notify PCC Engineer 4 weeks in advance. Testing Contractor - Compressive Strength - AASHTO T 22 - Flexure Strength of concrete (using simple beam with third-point Loading) - ASTM C 78 - Air Content - ASTM C 231 - Slump Flow - ASTM C 1611 - Passing Ability by J-Ring Method - ASTM C 1621 - Visual stability Index (VSI) - Appendix of ASTM C 1611 is required. NDOT Sampling and Testing two of the contractor’s trail tests. - Compression Strength - AASHTO T 22 - Flexure Strength of concrete (using simple beam with third-point Loading) - ASTM C 78 - Air Content - ASTM C 231 - Witness (Slump Flow & J Ring) Approval Contractor Submit data from lab testing to PCC Engineer. NDOT - Data review/ensure specifications are met - Approve mix design - Add to SiteManager with NDOT Mix Design Number Change to Admixtures in Approved Mix Design Testing/ Approval Contracto r Contractor is responsible to notify the PCC Engineer 3-4 weeks in advance. - Air Content - ASTM C 231 - Slump Flow - ASTM C 1621 - Passing Ability by J-Ring Method - ASTM C 1621 - Visual Stability Index (VSI) Appendix of ASTM C 1611 is required. NDOT - Air Content - ASTM C 231 - Witness Slump Flow, Passing Ability and Visual Stability Index
14.Plant Approval Requirements:
a.All Prestressed Concrete Stru ctural Units shall be produced in a Precast/Prestressed Concrete In stitute (PCI) certified plant.
b.All concrete for Precast/Prestressed Concrete Structural Units shall be produced at a PCI or NRMCA certified plant. Precast or Precast/Prestressed Concrete Structural Units 705.02 - 503 - (1) Whenever there is reason to suspect a problem with the equipment, any or all of the equipment may be inspected.
c.The method of manufacture and quality of concrete are also subject to Department approval/inspection.
d.A Contractor proposing to furnish Precast or Precast/Prestressed Structural Units sh all submit the following additional details to the Department concerning the method of manufacture:
1.Type, number, size, and location of the prestressing elements, and the name of the manufa cturer of the post-tensioning or pretensioning elements.
2.Complete information as to type, size, and method of installation of devices for anchoring post-tensioning elements. (3) The proposed manufacturing methods and the plans and design details of proposed casting beds and forms.
e.The use of portable pretensioning beds for the manufacture of concrete structural units or piles will not be allowed.
15.Mix Design Approval Requirements: a. The results of 15 individual trial mixes shall be produced using the same process as the plants normal production run. All test results of individual trial mixes shall be given to the Engineer. The test results collected shall include the following:
1.The release and 28-day compressive strength test results shall conform to AASHTO T 22.
2.The water/cement ratio. (3) The air content (between 2.0% and 6.0% inclusive). (4) The cement, fly ash, Slag Cement and Silica Fume content.
5.The amount of fine ag gregate, coarse aggregate, and sand and gravel. (6) Slump Flow test results shall conform to ASTM C 1611 (7) Passing Ability by J-Ring Method test results shall conform to ASTM 1621. (8) Visual Stability Index (VSI) test results shall conform to the Appendix of ASTM C 1611. (9) Flexure Strength of concre te at 28-day test results shall conform to (using simple beam with third-point loading) ASTM C 78. b. Any change of cement or aggregate source which must be on the Department’s Approved Product List shall require 5 new individual trial mixes. Refer to Table 705.04 for required testing procedures. c. Any changes using admixtures, the Contractor shall verify the properties of the concrete. Refer to Table 705.04 for the required testing procedures.
d.The compressive strength test results of 15 individual trial mixes shall be performed by the Contra ctor. An individual trial mix shall
705.02 Precast or Precast/Prestressed Concrete Structural Units
- 504 - consist of two sets of three cylinders with three cylinders being averaged at release and at 28-day. One set shall be taken within the first third of the load and the second set shall be taken within the two thirds of the load.
e.All tests for elastic modulus and compressive strength will be conducted using 4 inch x 8 inch (100 mm x 200 mm) cylinders.
f.The flexure strength test result s of 15 individual trial mixes shall be performed by the Contractor. An individual trial mix shall consist of two sets of two beams with two beams being averaged at 28-day. One set shall be taken within the first third of the load and the second set shall be taken within the two thirds of the load.
705.03 Construction Methods
1.The Contractor shall constr uct precast or precast/prestressed structures and piles as shown in the contract.
2.The Contractor shall provid e the Engineer a 4-week production schedule that is updated as necessary. If the Engineer is given less than 1 NDOT work day notice of a schedule change, then the fabricator may not proceed until the Engineer has reviewed the change. The Engineer may observe any or all of the procedures and shall have access to all reported data at any time durin g fabrication. The Engineer shall report any inconsistencies to the job superintendent.
3.The concrete producer shall report the following information for each load of concrete used to fabricate girders:
a.Brand, mill, type, certified test number, and weight of cement.
b.Brand, mill, class, certified test number, and weight of fly ash.
c.Type, source, location, weight, and free moisture content for each aggregate. Aggregate moisture shall be determined according to NDOT T 506 for each half day production.
d.Source, type, name, and amount of each admixture. e. Water added during batching and at placement site. f. Time, water and cement are initially mixed into the batch.
g.Time placement is started and completed.
4.Tensioning: a. Methods: (1) In all methods of tensioning, the stress induced in the prestressing elements shall be measured by the Contractor both with jacking gauges and by elongation of the element s; and these results shall be the same within a 5% tolerance.
2.Means shall be provided for measuring the elongation of reinforcement to at least the nearest 1/8 inch (3 mm).
3.All steel stressing devices, whether hydraulic jacks or screw jacks, shall be equipped with a ccurate reading calibrated pressure gauges, rings, or other devices as applicable to the jack being used.
4.All devices shall be calibrated and, if necessary, recalibrated to allow the stress in the prestressing steel to be computed at all times. Precast or Precast/Prestressed Concrete Structural Units 705.03 - 505 - (5) A certified calibration curve shall accompany each device.
6.Safety measures must be taken by the Contractor to prevent accidents due to possible breaki ng of the prestressing steel or the slipping of the grips during the prestressing process.
b.Measurement:
1.Pressure gauges, load cells, dynamometers, and any other devices used in determination of loads and/or pressures shall be accurate in their effective range within a 2% tolerance.
2.Such equipment shall be calibrated by an approved testing laboratory.
3.The Contractor's laborator y shall furnish calibration curves for each device and shall certify the curves as being accurate and verifiable.
4.The calibration of tensioning devices shall be accomplished in place.
5.The configuration of ja cks, gauges, and other components during calibration shall be exactly the same as during the actual stressing operation.
6.The method of calibrat ion shall be approved by the Engineer.
7.Tensioning devices shall be calibrated at least once a year and at any time a system appears to be operating in an erratic or inaccurate manner or gauge pressure and elongation measurements fail to correlate.
c.If the strand tension indicated by the gauge pressure and by elongation methods fail to agree within 5%, the operation shall be carefully checked and the source of error determined before proceeding further.
d.Measurement Consideration:
1.The Contractor's elongation and jacking pressure measurements shall make appropriate allowance for friction and all possible slippage or relaxation of the anchorage.
2.For pretensioned members, independent references shall be established adjacent to each anchorage by the Contractor to indicate any yielding or slippage that may occur between the time of initial stressing and final release of the cables.
3.The Contractor may te nsion straight post-tensioned tendons from one end. Curved tendons shall generally be stressed by simultaneous jacking from both ends.
e.In all stressing operations, th e Contractor shall keep stressing force symmetrical about the member's vertical axis.
5.Stressing Procedure:
a.Prestressing methods are shown in the contract. When the Contractor elects to use a method other than that shown in the contract, the Contractor shall submit complete shop plans for the proposed method.
b.Pretensioning Method: (1) The amount of stress to be given each strand by the Contractor shall be as shown in the contract.
705.03 Precast or Precast/Prestressed Concrete Structural Units
- 506 - (2) All strands to be prestressed in a group shall be brought to a uniform initial tension before being given their full pretensioning. This uniform initial tension of approximatel y 1,000 to 2,000 pounds (450 to 900 kg) shall be measured by a dynamometer or other approved means so that it can be used as a check a gainst the computed and measured elongation.
3.After initial tensioning, either single strand or multiple strand groups shall be stressed until the required elongation and jacking pressure are attained and reconciled within the 5% tolerance.
4.With the strand stressed in accordance with the contract, and with all other reinforcing in place, the Contractor shall cast the concrete to the lengths desired. Strand stress shall be maintained between anchorages until the concrete has reached the compressive strength specified in the contract.
c.Post-tensioning Method - Fo r all post-tensioned elements, the Contractor shall set the anchor plates ex actly normal in all directions to the axis of the bar or tensio ning strand. Parallel wire anchorage cones shall be recessed within the beams. Tensioning shall not be done until the concrete has reached the compressive str ength specified in the contract.
d.Combined Method - In t he event that the girders are manufactured with part of the reinforcement pretensioned and part post- tensioned, the applicable portions of the requirements listed above shall apply to each type.
6.Forms: a. Forms for Precast or Precast/Prestressed Concrete Structural Units shall conform to the requirements for concrete formwork as provided in Subsection 704.03.
b.Precast or precast/prestressed forms shall be accessible for the vibration and consol idation of concrete.
c.If the ambient temperatures are above 90 oF (32oC), precautions shall be taken so the forms , reinforcing steel and steel beams of structural units will be the ambient temperature.
7.Placing Concrete: a. The Contractor shall pr ovide the Department a 4-week production schedule that is updated as necessary. Unscheduled production changes may delay fabrication. Unscheduled production may result in rejection of Precast or Precast/Prest ressed Concrete Structural Units.
b.The Engineer may observe any or all of the procedures. The Contractor shall provide access to all reported data at any time during fabrication. The Engineer will repor t any inconsistencies to the job superintendent.
c.Concrete shall not be placed before completing the forming and placing of reinforcement.
d.Placing Procedure: (1) Concrete shall be placed continuously in each unit, taking care to avoid horizontal or diagonal planes of weakness. Precast or Precast/Prestressed Concrete Structural Units 705.03 - 507 - (2) However, if there is a de lay in delivery of concrete or for some other reason placement is interrupted for more than 30 minutes, then the concrete shall be rejected.
e.Consolidation:
1.Whether concrete requires vibration or self-consolidating concrete is used, special care shall be exercised to work and consolidate the concrete around the reinforcement and to avoid the formation of stone pockets, honeycombs and other defects.
2.Self-consolidated concrete (SCC) shall not be vibrated. Rodding of Self-consolidated concrete (SCC) is permissible in areas of tight reinforcement.
3.The other concrete shall be consolidated by vibrating. f. The concrete shall be a homogenous mixture and shall not contain cement balls.
g.The forms shall be overfill ed, the excess concrete screeded off, and the top surfaces finished to a uniform, even texture.
h.Each Precast or Precast/Pre stressed Concrete Structural Unit shall be stamped or marked with an identification number and its manufacture date.
i.Environmental Limitations: (1) The optimum range of c oncrete temperatures from the time the concrete is completely mixe d until the beginning of the presteam segment of the steam curing cycle shall be 50° to 95°F (10° to 35°C). Failure to operate within the optimum range shall be cause for curtailment of operations. During the presteam segment of the curing cycle, the temperature of the concrete shall not exceed 100°F (38°C) or fall below 50°F (10°C). These temperature restrictions apply when heat is supplied to the curing enclosure prior to initial set.
2.When placing concrete under cold weather conditions (ambient air temperature less t han 36°F [2°C]), the cold weather specifications in Sections 1002 and 704 shall be followed.
3.Forms and reinforcing materials shall be preheated to a minimum temperature of 40°F (4°C) and a maximum temperature not to exceed that of the concrete at the time of placement.
4.The Contractor may prehe at the drums of the mixer-trucks to the limits set for forms and reinforc ing, but under no condition shall heat be applied to the drums while they c ontain any of the batch materials or concrete.
8.Curing:
a.General:
1.The Contractor shall cure the concrete with wet burlap, waterproof covers, polyethylene sheets, or liquid membrane-forming compounds. Curing with liquid membrane-forming compounds shall be accomplished in accordance with the requirements of Section 1012 and Subsection 704.03, except that liquid membrane-forming compounds shall
705.03 Precast or Precast/Prestressed Concrete Structural Units
- 508 - not be used on that portion of precast/p restressed concrete girders, twin tees, or bridge beams upon which concrete will be cast later.
2.Water spray curing or other moist curing methods may be used subject to the approval of the Engineer.
3.The period of concrete curing shall be determined by the results of the compressive strengt h test on cylinders made during the progress of the work and cured to closely approximate the concrete strength of the product it represents.
4.Side forms may be removed 12 hours after placing the concrete, provided curing is continued with one of the approved Department curing procedures.
b.Steam or radiant heat will be allowed for accelerated curing provided the following procedure is adhered to:
1.Curing chambers shall be reasonably free of leakage and shall have a minimum clearance of 3 in ches (75 mm) in order to insure adequate circulation of heat. The relative humidity within the curing enclosure shall be maintained between 70 and 100%.
2.Temperature:
i.One approved continuous recording thermometer for each 115 feet (35 m) of casting bed, with a minimum of 2 continuous recording thermometers, shall be located in each enclosure or curing chamber. (ii) Continuous temperature record charts for each casting shall be available to the Engi neer for examination and approval at any time. (iii) If the temperature records or other temperature readings taken by the Engineer indicate that manual control of heat is producing temperature changes in exce ss of those specifi ed, the Engineer may reject the Precast or Precast/Prestress Structural Unit. (iv) Temperature of the curing concrete shall be 50°F to 105°F (10°C to 40°C) and shall be maintained near placement temperature until the concrete has reached initial set as determined by ASTM C 403 "Time of Setting of Concrete Mixtur e by Penetration Resistance". These temperature restrictions apply when heat is supplied to the curing enclosure prior to initial set.
v.The temperature rate of rise shall not exceed 60°F (15.5°C) per hour.
3.The concrete shall be completely enclosed with a waterproof curing chamber during accelerated curing periods.
4.Steam jets shall not be directed at the concrete or the steel forms.
5.If the temperature of the concrete rises above 175°F (79°C), the concrete shall be rejected.
6.The temperature in the concrete shall be maintained so that at any given time the difference between the highest and lowest Precast or Precast/Prestressed Concrete Structural Units 705.03 - 509 - temperature station readings will not be more than 30°F (-1°C). If the temperature varies more than 30°F (16°C), the product shall be rejected.
7.Eight hours after placing the concrete, individual sections may be uncovered to remove their forms. The curing may be discontinued during this operation. The section shall not be left uncovered longer than necessary and never longer than 30 minutes. Waterproofed covers shall be used to recover the product.
8.After the heat source has been turned off, the curing cover shall be maintained in place during the curing period until the release strength has been reached.
9.Detensioning shall be accomplished before the temperatures of the units drop more than 60oF (34ºC) from the peak cure strength temperature and while they are still moist.
10.Master slave heat curing system may be used for curing quality control cylinders.
c.After detensioning, prestressed concrete girders shall be inspected for cracking. If any cracks ar e discovered between quarter points in the middle of the girder on the bottom flange face, the girder shall be rejected.
9.Defects and Repair Procedures:
a.After the forms are removed, stone pockets, honeycombs, or other defects may be exposed. The Engineer shall determine if these defects affect the item's structural integrity and whether the item will be rejected.
b.Precast or Precast/Prestre ssed Concrete Structural Units which have chipped, spalled, honeycom bed, or otherwise defective areas which are not considered detrimental to the structural integrity may be used after being repaired by the Grooming and Repair Procedures for Precast Concrete Products in the Department’s Materials Sampling Guide.
10.Surface Finish:
a.On structures serving as highway grade separations, the following shall apply:
1.The exterior face of all exterior girders or beams plus the bottoms and chamfers on all lower flanges shall be given the following finish:
i.All uneven form joints in excess of 1/8 inch (3 mm) shall be ground smooth. (ii) The surface shall be steel brushed to remove scale, laitance, and to open partially obstructed holes. (iii) The surface shall be dampened. (iv) Grout shall be applied to the surface. (v) The grout shall consist of 1.5 parts of fine sand, 1 part of Portland cement, and sufficient wate r to produce a consistency of thick paint. The cement used in the grout shall be a blend of regular Type I and white Portland cement to duplicate the lighter appearance of the steam cured units.
705.03 Precast or Precast/Prestressed Concrete Structural Units
- 510 - (vi) If necessary, an admixture which will not discolor the concrete may be used in the grout to reduce shrinkage if approved by the Engineer. Admixtures containing iron particles shall not be used. (vii) The surface shall be float finished with a cork or other suitable float. This operation shall completely fill all holes and depressions on the surface. (viii) When the grout is of such plasticity that it will not be pulled from holes or depressions, sponge rubber or burlap shall be used to remove all excess grout. (ix) Surface finishing during cold weather shall not be performed unless the temperature is 40°F (4°C) and rising. The surface shall be protected against temperature drops below 40°F (4°C) for a period of 12 hours after finishing.
x.A uniform appearance will be required. In the event the appearance produced by the above procedure is not uniform, both in texture and coloration, the precast or pr ecast/prestress structural unit will be rejected. The Contractor may request other methods approved by the Engineer to create a uniform appearance.
11.Grouting for Post-Tensioned Units:
a.The Contractor shall install st eel in flexible or other approved tubes which shall be cast in the concrete and shall be pressure-grouted after the post-tensioning process has been completed.
b.Bonding grout shall be made to the consistency of thick paint and shall be mixed in the proportions as follows: Portland cement (Type I), 100 pounds (45 kg); fly ash (ASTM C 618), 34 pounds (15 kg); water, 45 to 62 pounds (20 to 28 kg) (adjust at site); and nonshrink admixture approved by the PCC Engineer.
c.The final grouting pressure shall be at least 80 psi (550 kPa). d. The Contractor shall make provisions to demonstrate to the Engineer that grouting material has co mpletely filled all areas within the conduit.
13.Handling, Transporting, and Storing: a. (1) Prestressed concrete st ructural units must be at least 9 days old before they can be set on the bridge substructure. Surveying for shim shots, forming the bridge deck or diaphragms and placing construction material on the girder is not allowed until the girders have attained the minimum age and design strength specified in the contract.
2.The Contractor shall be responsible for exercising extreme care in lifting, handling, storing and transporting the prestressed concrete structural units to prevent cracking or damage. Prestressed concrete bridge girders shall be maintained in an upright position and supported within 18 inches of the ends at all times. When supported at the proper positions, no part of the units shall be allowed to rest on the ground. Prestressed concrete bridge girders shall be set on a level area to prevent field bowing and adequate supports shall be placed under their bearing devices to prevent settlement into the ground. Prop er support bearings shall be used to avoid twisting of the prestressed c oncrete bridge girders. Prestressed Precast or Precast/Prestressed Concrete Structural Units 705.03 - 511 - concrete structural units shall be lifted by devices designed by the Contractor.
3.The Contractor must provide any temporary intermediate diaphragms and/or bracing necessary to provide lateral and torsional stability for the girders during constr uction of the concrete slab. The temporary intermediate diaphragms/br acing shall be removed after the concrete has attained its design strengt h. The cost of furnishing, installing and removing the temporary intermedi ate diaphragms and/or bracing shall be subsidiary to the pay item “Class 47BD-_____ Concrete for Bridges”.
4.(i) The girders shall be transported in an upright position and the points of support and direction of the reactions with respect to the girder shall be approximately the sa me during the transportation and storage as when the girder is in its final positi on. If the Contractor finds it necessary to transport the precast girders in some other position, the Contractor shall be prepared to prove that no internal damage results. (ii) Adequate padding shall be provided between tie chains and cables to prevent chipping of the concrete. (iii) Live loads shall not be allowed on the superstructure units until the floor slab is placed and attains the design strength shown in the contract.
13.Inspection Facilities: The Contractor shall arrange with the producer of Precast or Precast/Prestressed Concrete Structural Units to provide an office, laboratory, and bathroom for the Department's inspector. The areas shall meet the following requirements:
a.Thermostatically controlled heating and air conditioning shall be provided so that temperature c an be maintained between 68° and 77°F (20° and 25°C).
b.The floors shall be tile or a similar floor covering. c. Interior and exterior walls shall be well maintained and painted.
d.All exterior doors shall have cylinder locks, and all keys shall be turned over to the Engineer.
e.Ceiling lighting shall prov ide a minimum of 465 foot-candles (5000 lx) of light on all working surfaces.
f.Electrical outlets shall be spaced no more than 6 feet (1.8 m) apart with no less than 1 outlet on any wall of the office or lab.
g.A single trunk telephone and a means to the internet with a minimum of 1.5 mb of download stream shall be installed in the office, and the installation charges shall be paid by the Contractor. The monthly service charges will be paid by the Department.
h.A fire extinguisher and First-Aid kit shall be provided. i. A ventilated bathroom with a toilet and sink shall be provided in the structure. A fresh water supply and drain will be required in the lab area.
j.The lab, office, and bathroom shall be separate rooms with interconnecting doors.
705.03 Precast or Precast/Prestressed Concrete Structural Units
- 512 - k. The minimum lab area is 230 square feet (21 m2).
l.The minimum toilet area is 20 square feet (2 m2).
m.The minimum office area is 160 square feet (15 m2).
n.The Contractor shall clean and maintain the rooms and shall supply all heating fuel, electricity, and water.
o.The Contractor shall also supply for the sole use of the inspectors all desks, work tables, chairs , files, lockers, and sanitary supplies necessary and commensurate with the inspection of his/her plant. It is anticipated that the following minimum amount of office and lab equipment will be required: One desk with approx imately 3 foot x 6 f oot (0.9 m x 1.8 m) top; one upright locker or wardrobe, wi th shelves, approximately 5 feet (1.5 m) deep; two 4-drawer file cabinets; 1 chair per inspector; 10 square feet (1 m2) of work surface per inspector in the office area; and a lab counter (approximately 3 x 18 feet [0.9 m x 5. 5 m]) with storage space beneath.
705.04 Method of Measurement
1.Precast or Precast/Prestressed Concrete piles shall be measured in accordance with the requirements of Section 703.
2.Precast or Precast/Prestressed Concrete superstructures will be measured for payment by the lump sum.
705.05 Basis of Payment
1.Prestressed or Precast Concre te piles shall be measured and paid for as described in Section 703.
2.P a y I t e m P a y U n i t Precast/Prestressed Concrete _____ Superstructure at Station ______ Lump Sum (LS)
3.Reinforcing steel, prestressing tendons, and all other components of the Precast or Precast/Prestre ssed Concrete superstructure are subsidiary to this pay item.
4.The cost of furnishing and maintaining the inspection facilities will not be paid for directly, but shall be subsidiary to "Precast/Prestressed Concrete _____ Superstruct ure at Station _____".
5.If a Precast or Precast/Prest ressed Structural item's 56-day compressive strength is less than the desi gn strength, then the Engineer will determine if the item can be used. If the item is to be used, a payment deduction of 25% will be taken if the 56-day compressive strength is less than 95% of the design strength.
6.All equipment calibrations and tests are subsidiary to "Precast/Prestressed Concrete _____ Superstructure at Station _____".
7.Payment is considered full compensation for all work described in this Section, including the cost of prestressing and precasting. - 513 - SECTION 706 -- CONCR ETE BRIDGE FLOORS
706.01 Description
1.This work shall consist of providing all necessary materials and construction of concrete bridge floors in accordance with the contract and specifications.
706.02 Material Requirements
1.Reinforcement shall be furnished, handled, and placed in accordance with the requirements of Section 707.
2.White polyethylene film shall comply with the requirements of Section 1010.
3.Concrete retardants shall meet the requirements of Sections 1002 and 1007.
4.Concrete shall meet the requirements of Section 1002.
706.03 Construction Methods
1.Reinforcement Steel:
a.Before placing concrete for bridge floors, the placement of top reinforcing steel shall be checked for clear ance to the surface of the slab by measuring from the reinforcing steel to the strike-off screed.
b.Such checking shall be done by the Contractor in the presence of the Engineer and shall be repeated at a sufficient number of locations to demonstrate that concrete cover over the reinforcing steel as required in the contract will be obtained at all points on the slab.
c.Such checking does not preclude subsequent checks by the Engineer during and after concrete placement.
2.Environmental Conditions: a. The Contractor shall perfor m bridge floor construction in accordance with the requirements of Se ction 704. Bridge floor concrete shall not be placed when the anticipated wind velocity during the concrete placement period is expected to exceed the limitations shown in Table 706.01. Table 706.01 Temperature and Wind Velocity Limitations Air Temperature in the Shade Maximum Wind Velocity 90°F (32°C) 10 mph (16 kph) 77°F (25°C) 16 mph (25 kph) 68°F (20°C) 22 mph (35 kph) 59°F (15°C) 28 mph (45 kph) 50°F (10°C) 40 mph (65 kph)
b.Bridge floor concrete shall not be placed when the ambient air or concrete temperature is above 90°F (32°C).
Source: Nebraska Standard Specifications for Highway Construction, 2017 Edition. Pages 532–546 of 1,048.