5-141 SECTIO N 510 – PRESTRESSE D CONCRETE 510.0 1 DESCRIPTION . This work shall consist of manufacturing, transporting, and erecting precast prestressed concrete members. 510.0 2 MATERIALS . Materials shall meet the requirements of the following subsection s: Portland Cement ................................ ................................ ................................ ......... 701.02 High Early -Strength Portland Cement ................................ ................................ .......701.0 3 Portland -Pozzolan Cement ................................ ................................ ......................... 701.0 4 Portland -Limestone Cement ................................ ................................ ...................... 701.0 5 Portland Blast -Furnace Slag Cement ................................ ................................ ......... 701.0 6 Ternary Blended Cement ................................ ................................ ........................... 701.0 7 Fine Aggregate for Concrete ................................ ................................ ...................... 704.01 Coarse Aggregate for Concrete ................................ ................................ .................. 704.02 Lightweight Fine Aggregate for Concrete ................................ ................................ .704.19 Mortar, Type IV ................................ ................................ ................................ ......... 707.0 1(e) Preformed Joint Filler, Cork, and Asphalt -Treated Felt ................................ ............ 707.0 6 Polyvinyl Chloride (PVC) Waterstop ................................ ................................ ........ 707.08 Bar Reinforcement ................................ ................................ ................................ .....713.01 Prestressing Strand and Post -Tension ing Strand ................................ ....................... 713.0 4 Structural Steel ................................ ................................ ................................ ........... 714.02 High -Strength Low -Alloy Structural Steel ................................ ................................ 714.03 Carbon Steel Bolts, Nuts, and Washers ................................ ................................ .....714.04 High -Strength Structural Bolts and Assemblies, 120 ksi ................................ ........... 714.05 Concrete Curing Materials ................................ ................................ ......................... 725.01 Air-Entraining Admixtures ................................ ................................ ........................ 725.02(b) Retarding Admixtures ................................ ................................ ................................ 725.02(c) Water -Reducing Admixtures ................................ ................................ ..................... 725.02(e) Water -Reducing and Retarding Admixtures ................................ .............................. 725.02(f) Water -Reducing, High Range Admixtures ................................ ................................ 725.02(g) Water -Reducing, High Range, and Retarding Admixtures ................................ .......725.02(h) Accelerating Admix tures ................................ ................................ ........................... 725.02(i) Water -Reducing and Accelerating Admixtures ................................ ......................... 725.02(j) Specific Performance Admixtures ................................ ................................ ............. 725.02(k) Mineral Admixtures ................................ ................................ ................................ ...725.03 Polystyrene Insulation Board ................................ ................................ ..................... 735.01 Blanket Insulation Material ................................ ................................ ........................ 735.02 Pipe Insulation ................................ ................................ ................................ ........... 740.0 6 Water ................................ ................................ ................................ .......................... 745.01 Concrete Repair Material , Type I ................................ ................................ .............. 780.0 1(a) Bearing pads for structures shall meet the requirements of Section 731 . 5-142 510.0 3 GENERA L FABRICATIO N REQUIREMENTS .
a.General Requirements . The manufacture of the prestressed units shall be in accordance with the requirements of PCI MNL -116 and PCI MNL -135, except as modified in this section .
b.Qualification . The prestressed members shall be manufactured in a plant that has been certified by PCI under its Plant Certification Program for prestressed concrete. The plant shall be certified at a minimum to the level of product being produced. If there is an archi tectural finish for the product, the plant shall be certified at a minimum to the level of product being produced plus the architectural certification at that level. Prestressed concrete shall be manufactured in a plant that maintains a quality control laboratory that meets the requirements of the Agency’s Qualified Laboratory Program . As a minimum, the laborat ory shall be equipped with a compression testing machine, curing room or chamber, apparatuses for measuring slump/flow and air entrainment, and a complete set of Aggregate sieves. The compression testing machine shall be calibrated yearly by an independent laborat ory using equipment that is certified by the National Institute of Standards and Technology. The testing machine shall be power -operated and capable of applying the load continuously rather than intermittently, and without shock.
c.Quality Contro l. The fabricator shall demonstrate a level of quality control testing that satisfies the Agency as to its ability and commitment to produce concrete to the requirements of this section . A satisfactory program of quality control shall include gradation and moisture determinations of the aggregates, as well as slump, air content, and strength determinations of the concrete. These tests shall be performed at regular and suitable intervals as specified in the Materials Sampling Manual and actively used to main tain the quality of the concrete within the specified requirements. The fabricator shall have a plant specific quality control plan approved by the Agency prior to the beginning of any fabrication activities. 510.0 4 SUBMITTALS . As soon as practical after award of the Contract, all required information shall be prepared and submitted. Fabrication drawings, also referred to in the precast industry as production drawings or shop drawings, for the prestressed concrete shall be sub mitted in accordance with the requirements of Subsection 105.06 , with an additional copy sent to the Structural Concrete Engineer. Fabrication drawings shall include such detail as needed to fully describe the intended as -built condition of the prestressed elements including any connections between prestressed elements or existing structures and materials. 5-143 In addition to the requirements in Subsection 105.06 , the following shall be included:
a.Concrete Mix Design . The concrete mix design submittal shall include, but not be limited to, the following items:
1.Batch weights specifying dry or saturated surface dry.
2.Material names and sources.
3.Aggregate prop erties and testing dates. Aggregates shall be tested on an annual basis, at a minimum, to verify that they meet the requirements of AASHTO T 84 and AASHTO T 85 for absorption and specific gravity and AASHTO T 19 for unit weight.
4.Chemical and physical properties of cementitious materials.
5.Admixture names and sources.
6.Lab data that shall include, but not be limited to, the following items:
a.The maximum W/CM ratio that will be allowed during production, including water contributed to hy dration by all admixtures, when the cumulative total exceeds 1 gallon per cubic yard. All mix qualification test results shall be generated with concrete from batches that are produced at this maximum W/CM ratio.
b.The slump/spread minimums and maximums , as determined from trial batches. The concrete shall be classified and tested as self-consolidating concrete (SCC) if the minimum spread is at least 18 inches. When the concrete is tested as a n SCC mix, the difference between the J -ring test (ASTM C1621 ) and the spread test (ASTM C1611 ), shall be 2 inches or less for the minimum and maximum spread. Concrete that fails to meet the 18 inches minimum spread threshold will be classified and tested as conventional concrete. The visual stability index (VSI) determination will be included for the minimum and maximum values and shall not be greater than 1. The concrete shall not demonstrate segregation at the minimum or maximum slump/spread.
c.Air content results obtained in accordance with the requirements of AASHTO T 152 . 5-144 d. Temperature results obtained in accordance with the requirements of ASTM C1064 .
e.Cylinder compression stress results obtained in accordance with the requirements of AASHTO T 22 for early breaks and design strength, and 28 -day standard cure results obtained in accordance with the requirements of AASHTO R 100 . The type of cure shall be l isted for each age of break.
f.The surface resistivity of the test mix shall be measured at 56 days based on the requirements of AASHTO T 358 . Results shall be categorized as Low, Very Low, or Negligible in accordance with AASHTO T 358, Table 1. The surface resistivity may be accepted prior to 56 days if the results meet these requirements. The 56 day test results shall be completed and submitted regardless of the results of earlier tests. Testing shall be performed by an independent AASHTO re:source qualified laborat ory. Test results that are suspected to have been adversely affected due to the presence of polymeric admixtures in the proposed mix may be retested with the polymeric admixture omitted.
g.The alkali -silica reactivity (ASR) of each type of aggregate shall be measured separately based on the requirements of AASHTO T 303 . If one or more of the aggregates exceeds 0.10% expansion, then the aggregate shall be tested again according to the requirement s of ASTM C1567 . The Contractor may elect to go directly to ASTM C1567 testing if they suspect that the aggregate may exceed the 0.10% expansion if tested by AASHTO T 303. Testing shall be performed by an independent AASHTO re:source qualified laborat ory accredited in the specific test method.
h.Length change test results obtained in accordance with the requirements of AASHTO T 160 . Testing shall be performed by an independent AASHTO re:source qualified laborat ory accredited in conducting testing that mee ts the requirements of AASHTO T 160 . The maximum free shrinkage test result shall not exceed 0.06%. The cross -section of the prism shall be 4 inches × 4 inches. The requirements of AASHTO T 160 , Section 11.1.2 shall be followed for storage and measurements. 5-145 (7) Mix design approvals will be valid for a 12 -month period. The approved mix design will be allowed re -approval if the following conditions are satisfied:
a.A determination has been made that no material proportioning or material sources have changed from the initial approved mix design.
b.The mix design for re -approval is submitted with updated aggregate properties and volumes adjusted accordingly. The properties to be tested include , but are not limited to, specific gravity, unit weight, and absorption. Aggregate property values will be valid for 14 months from the date tested.
c.The re -approved mix design shall be accompanied by the test mix data that was completed and accepted for the in itial mix design approval, as well as any applicable updated test information. New mix designs and mix designs that were initially approved more than 36 months ago shall have new testing completed to be submitted for approval. The proposed concrete mix des ign, including performance history and all requests for variance from th e material requirements of these specifications, shall be submitted for approval. The Structural Concrete Engineer may require a minimum of 8 weeks for testing, review, and approval of new mix designs.
b.Dimensions and Tolerances . The dimensions and tolerances of the sections to be fabricated shall be submitted. Fabricators shall calculate the camber estimate at the time of release and at the estimated time of delivery. The camber control plan shall be as detailed in Subsection 51 0.08( i).
c.Locations . The locations of reinforcing steel and prestress ing strands shall be submitted.
d.Prestressing Methods . The methods of prestressing, including certified calibration charts for all jack and gauge combinations shall be submitted.
e.Tensioning Calculations . Tensioning calculations for prestress ing strands that include gauge pressure, elongations, and movement of anchorage abutments. A professional engineer shall review and stamp the calculations.
f.Strand De -Tensioning . The method and sequence of strand de -tensioning. 5-146 (g) Surface Finish . The type of surface finish and how the finish will be obtained.
h.Curing Method . The curing method, detailing the sequence and duration in accordance with the requirements of Subsection 510.09 .
i.Minimum Strength Requirement . The minimum required concrete strength for the transfer of prestress forces.
j.Lifting Attachments . The design of the lifting attachments, including the minimum required concrete strength to allow lifting, based on calculations stamped by a professional engineer . Lifting attachments are not required to be permanently installed in the work and may be removed or left in place at the Contractor’s convenience, provided that the minimum clear cover requirements are met.
k.Logistics . Transportation, handling, and storage details.
l.Installation and Grouting . The installation and grouting procedures.
m.Quality Control . A full description of all quality control procedures. All design details shall be in accordance with the VTrans Structures Design Manual and the AASHTO LRFD Bridge Design Specifications. A professional engineer shall stamp any design calculations included in the submittal materials.
510.05 Concrete .
a.Batch Plants . Batch plant equipment, materials, and batching procedures shall conform to the provisions of Section 501 identified in Table 510.05A . 5-147 TABLE 510.05A – BATCH PLANT OPERATION SUBSECTIONS AND TOPICS Subsection Topic Subsection 501.04 (a) General Requirements 1 Subsection 501.04( d) Testing Laboratory Subsection 501.04( e) Bins and Scales Subsection 501.04( f) Production Tolerances for Batching Subsection 501.04( g) Storage and Proportioning of Materials Subsection 501.05 Mixing and Delivery 2 1 Paragraphs 1 and 3 only. 2 For plants not located in Vermont, the Agency has the option of waiving the requirements of Subsection 501.05(a)( 6) in their entirety and Subsection 501.05(c) , paragraph 1 only.
b.Acceptance Testing . For acceptance testing, refer to the Materials Sampling Manual for sampling, curing, and testing requirements. Specimens shall be tested either at the Agency’s Materials Testing and Certification Section Central Laboratory, or at the fabricator’s plant laborat ory. An Agency representative shall witness all tests. Concrete for prestressed members shall conform to the following:
1.The compressive strength test results obtained at or before 28 days shall not be less than the design compressive strength shown on the Plan s. When a 28 -day test result is below the specified design strength, all concrete represented by that test shall be unacceptable for the requirements of this section . The Engineer reserves the right to reject all members that were manufactured from this concrete.
2.The maximum total water batched shall not exceed 280 pounds per cubic yard, including water contributed to hydration by all admixtures when the cumulative total exceeds 1 gallon per cubic yard. If total cementitious material content exceeds 900 pounds per cubic yard, then water batched shall not exceed 300 pounds per cubic yard. The maximum W/CM ratio in pro duction shall not exceed the maximum W/CM ratio specified in Subsection 510.04(a)(6)a. 5-148 (3) The air entrainment value shall be 7% (± 2% ) when tested in accordance with AASHTO T 152.
4.The temperature of the concrete at the time of placement shall be between 50°F and 85°F as tested in accordance with the requirements of AASHTO T 309 .
5.The concrete shall not demonstrate segregation at any time. If the mix fails to remain within the min imum and maximum slump or spread ranges submitted in the mix design, the load may be rejected. The VSI shall be less than or equal to 1.
6.The Agency may request that the producer fabricate three concrete test cylinders that will be cured along with the piece they represent through the complete curing period. These cylinders shall be kept with the piece they represent until collected by the Agency as specified by the requirements of AASHTO T 277 and AASHTO T 358 .
c.Cementitious Materials . Only the cemen titious combinations and sources from the approved mix design shall be used in the prestressed units required for any one structure, unless otherwise authorized by the Structural Concrete Engineer. Any admixture containing calcium chloride shall not be use d. 510.0 6 INSPECTION . Materials furnished and the work performed under the requirements of Section 510 shall be inspected by the Agency. The inspector shall have the authority to reject any material or work that does not meet the requirements of these specifications. Any work performed that has not been inspected may be rejected, unless waived in writing by the Engineer. The inspector shall be provided with a minimum office space of 100 square feet with a least dimension of 6 feet. A desk surface with a minimum of two drawers , as well as dedicated private telephone and internet services, shall be provided to the laboratory. The phone and internet service shall be provided in accordance with Subsection 631.02(a)(4) , except that selection of the service by the Engineer is not required . Any variances shall be approved by the Structural Concrete Engineer. This office space shall be located on the premises as close to the production area as practicable. The Engineer reserves the right to reject inadequate office facilities and require suitable alternatives. 5-149 510.0 7 PRESTRESSING . Prestressing shall be accomplished by the pre -tensioning method. The fabricator shall provide all equipment necessary for the prestressing operations. Prestressing shall be done with approved jacking equipment. Hydraulic jacks shall be equipped with pressure gauges or other indicating devices. The combination of jack and pressure gauge, or other tensioning system, shall be accompanied by a certified calibration chart showing the r elationship between the gauge reading and the force in the ram for both ascending and descending movements of the ram. The calibration date of each combination jack and gauge or indicating device shall be within the 12 -month period immediately prior to the start of work. If other types of jacks are used, calibrated proving rings or other devices shall be furnished so that the jacking force may be accurately determined. Suitable precautions shall be taken by the fabricator to prevent accidents due to breakin g of the prestressing steel or slippage of the grips during prestressing operations. The tensioning operation shall proceed until the calculated gauge reading has been reached. The elongation of each strand shall then be measured. If the measured elongatio n differs from the theoretical by more than 5%, the tensioning operation shall be stopped, and the cause of the discrepancy determined prior to continuing. Immediately after tensioning, the final position of each strand shall be marked to check any strand slippage prior to placing concrete. If slippage is suspected or if the time between tensioning and placing concrete exceeds 48 hours, then 10% of the total number of strands including the strands that are suspected to have slipped shall be re -tensioned and the elongation measured. The specific strands to be re -pulled will be selected by the Agency inspector , but no fewer than two strands shall be re -pulled. If additional elongation is gained, the amount gained shall be subtracted from the theoretical elonga tion. If the result of the theoretical elongation minus the gain in elongation is less than the minimum allowable elongation per the requirements of PCI MNL -116 for any of the strands tested, the final force shall be applied to all strands. For abutment anchorage set -ups where the strands are anchored to abutments that are independent from the form, thermal adjustments shall be made if the ambient temperature at the time of tensioning differs by more than 25°F from the concrete temperature prior to placement and if the net force differential is greater than 2.5%. Consideration shall be given to partial bed length usage and adjustments made when the net effect on the length of the bed used exceeds the allowable. The thermal coefficient of steel sha ll be taken as 6.5 × 10-6/°F. 5-150 510.0 8 FABRICATION .
a.Pre-Production Meeting . A pre -production meeting shall be requested by the producer a minimum of 14 calendar days prior to beginning concrete placement, unless the Engineer deems, in writing, that a pre -production meeting is unnecessary. The meeting shall be held a minimum of 5 calendar days prior to beginning concrete placement unless otherwise approved by the Struc tural Concrete Engineer. At a minimum, t he pre -production meeting shall be attended by the crew supervisor, plant manager, inspector or inspector ’s supervisor, a represent ative from the Agency’s Materials Testing and Certification Section Structural Concrete Unit, and the Project Manager or designer . Additionally, the fabricator shall have available at the pre -production meeting the approved fabrication drawings and a complete anticipated production schedul e for all components included in the fabrication draw ings.
b.Forming Members . Side forms shall be supported without the use of ties or spreaders within the body of the member. Any defects or damage due to formwork, stripping, or handling may be cause for rejection. Forms for interior voids or holes in the members shall be constructed of a material that will adequately resist breakage or deformation during concrete placement and that will not materially increase the weigh t of the members. Interior void forms shall be accurately positioned as shown on the Plan s and secured to prevent displacement during concrete placement. All voids shall be adequately vented to prevent damage to the members during curing. Each void shall co ntain a suitably located drain hole. Holes or cutouts for anchoring devices, diaphragm connections, openings for connection rods, recesses for grout holes for railing bolts, and any other related details shown on the Plans shall be provided for in the memb ers. Where diaphragm dowels do not pass through the member, the dowels may be attached by use of an approved anchorage embedded in the concrete member.
c.Placing Transverse Conduits and Tendons . Each tendon to be post -tensioned shall be encased in an app roved conduit. Unless otherwise shown on the Plans, the ratio of cross -sectional area of the tendon to be encased to the interior cross -sectional area of the conduit shall not exceed 0.4, except when a steel bar is used as a tendon. The inside diameter of the conduit shall be at least 3/8 inch greater than the diameter of the bar. Conduit that has been crushed or has opened seams shall not be used. 5-151 The conduit shall be rigidly constructed, completely sealed, accurately placed, and securely fastened to maintain the desired profile during concreting. No conduit shall be located more than 1/4 inch from the position shown on the Plans. Bundling of condui ts will not be permitted.
d.Placing Pre stressing Strands . Prestress ing strands shall be accurately placed in position to achieve the center of gravity of the steel as shown on the approved shop drawings. Prestress strands shall be protected against corro sion and be free of nicks, kinks, dirt, rust, oil, grease, and other deleterious substances.
e.Bar Reinforcement and Welded Wire Reinforcement . Bar reinforcement and welded wire reinforcement shall be furnished and installed in conformance with the requirements of Section 507. The chairs or spacers used to support or locate the reinforcement that bears on the faces of the forms shall be made of, or be coated with, a non -corrosive material so that no discoloration will show on the faces of the prestressed concrete units.
f.Pre-Tensioning . The prestress ing strands shall be stressed by jacking in accordance with the requirements of Subsection 5 10.07 , and in the presence of an Agency representative. The jacking force exerted and the elongation produced shall be recorded. Several units may be cast and stressed at one time in a continuous line. Sufficient space shall be maintained between the ends of the units to permit access for cutting strands after the concrete has attained the required strength.
g.Placing Concrete . Concrete shall not be deposited in the forms until the Agency representative has reviewed and approved the placement of the reinf orcement, conduits, anchorages, and prestressing strands. The concrete shall be vibrated internally, externally, or a combination thereof to the required consolidation. The vibrating shall be done with care and in such a manner that the concrete is uniform ly consolidated, any displacement of or damage to reinforcement, conduit, voids, and prestressing strand is avoided, and acceptable finish surfaces are produced. When a vibrator is used with rebar with special coatings or made of non -metallic material or material that could be susceptible to damage, the vibrator head shall be non -metallic or rubber - coated. SCC concrete should not be vibrated. If there is a need to vibrate SCC concrete, it shall only be vibrated for the minimum time necessary so as to avoid segregation. 5-152 (h) De-Tensioning . No stress shall be transferred to the concrete until 80% of the design compressive strength (f′ c) has been attained, or as stated on the approved fabrication draw ings. The compressive strength shall be determined by cylinders tested in accordance with the Materials Sampling Manual . The prestressing strands shall be released in the de -tensioning pattern detailed on the shop drawings. If de -tensioning is accomplished by single strand release, each strand shall be cut by gradually heating the strand at both ends of the member simultaneously. A minimum length of 5 inches of strand shall be heated to prevent any shock or snap when the strand is finally severed. Each stra nd shall be cut at all spaces between members cast continuously, before starting de -tensioning on the following strand in sequence. Strands shall be cut flush and epoxy -painted unless otherwise specified on the Plans. If the strands are required to be recessed, a block -out shall be built into the bulkhead that will allow the strands to be cut without damaging the concrete. The recess s hall be thoroughly cleaned and patched with Type IV mortar . The mortar shall be wet cured for three days or as specified by the manufacturer.
i.Dimensional Tolerances . All dimensional tolerances shall be in accordance with PCI MNL -116 and PCI MNL -135 unless otherwise noted in the Contract or approved by the Engineer. The camber and differential camber between beams measured at pre -shipping inspection shall be within PCI tolerances and shall be measured with dunnage placed under bearing areas of the beam and at no less than 72 hours after the removal of any means of camber correction. Tolerances shall be compared to the calculated camber estimates at the time of the pre -shipping inspection. The camber control plan shall detail how the fabricator will achiev e the calculated camber estimate submitted in the fabrication draw ings as required in Subsection 510.04(b) . The fabricator shall achieve a beam camber at time of delivery that is within PCI tolerances of the calculated camber estimate. In addition, it is the responsibility of the Contractor to confirm at the time of fabrication drawing review that the calculated camber estimate is compatible with the grades and elevations of the rest of the structure.
j.Dimensional Tolerances for Prestress Deck Panels . Prestress deck panels shall have dimensional tolerances as specified in Table 510.08A . 5-153 TABLE 510.08A – PRESTRESS DECK PANEL TOLERANCES Element Tolerance Vertical position of strand group (measured from bottom of panel) + 0 inches, - 1/8 inch Dunnage ± 6 inches Warping (distance from nearest adjacent corner) 1/16 inch per foot Finish of strands (minimum extension beyond ends of panel) 4 inches
k.Defects . Units that contain defects caused by manufacture or handling may be repaired at the manufacturing site. Minor defects are defined as the intermittent presence of holes, honey -combing, chips, or spalls, which measure 6 inches or less in the longest dimension, and that do not penetrate deeper than 1 inch into the concrete. Minor defects may be repaired using a n approved standard repair proc edure as detailed in Subsection 510.08(k)(3) . Surface voids or bug holes that are less than 5/8 inch in diameter and less than 1/4 inch deep need not be repaired. Minor defects that recur with any identifiable regularity or pattern may be required to be addressed through a non-conformance report (NCR) , at the discretion of the Structural Concrete Engineer. Any defect that has the potential to affect structural capacity or integrity shall be categorized as a major defect. It is at the sole discretion of the Structural Concrete Engineer to determine into which category any defect is categorized.
1.Cracking . Cracks less than 0.01 inch in width shall be sealed by a method approved by the Structural Concrete Engineer. Cracks equal to or greater than 0.01 inch in width may be cause for rejection based on th eir width, length, location, and frequency. At the Structural Concrete Engineer’s discretion, cracked members shall be repaired or replaced at the Contractor’s expense. De -tensioning procedures causing web -splitting or other member cracking shall be revise d before de -tensioning the next bed. Cracks with a width of 0.05 inch and greater found in any member will be cause for rejection. 5-154 (2) Repairs . Repairs shall be made using an overhead and vertical concrete repair material from the Agency’s Approved Products List . Any unsound concrete shall be carefully chipped out and the perimeter saw -cut to a minimum depth of 1/4 inch or deeper if recommended by the repair material manufacturer. The prepared surface profile shall be as specified by the repair material manufacturer. If not specified , the prepared surface profile shall conform to, at a minimum, the International Concrete Repair Institute ’s CSP 6 (Medium Scarification) surface profile . The repair material shall be cured as specified by the manufacturer.
3.Standardized Repair Procedures . Standardized repair procedures (SRPs) shall be a comprehensive documented process for repairing minor defects a t the fabricator’s facility. At a minimum, the SRP shall detail the scope of defects for which that procedure is intended to be used, a detailed narrative including every step of the repair procedure, and the product documentation for the specific repair materials that will be used. The SRP shall include exampl e pictures of defects for which the procedure could be used, detailed example pictures covering every step of the repair procedure, and example pictures of a successfully completed repair job. Approval to use an SRP for any given defect is at the sole disc retion of the Structural Concrete Engineer, and all SRPs shall be approved by them prior to their use. SRPs shall be submitted to the Structural Concrete Engineer at least 14 calendar days in advance of the repair work. The Agency’s consent to use a n SRP f or the repair of a defect does not constitute acceptance of that repair.
4.Non-Conformance Report . Any defects existing in the pieces, other than those defined as minor above, shall be documented with a non-conformance report (NCR) . NCRs shall be submitted within 2 working day s of the discovery of the defect. At a minimum, the NCR shall detail what the defect is, including detailed pictures of the piece and defect, and what caused it. The NCR shall further document the proposed repair, the proc edure for carrying out the proposed repair, and a plan of action to prevent additional similar defects from occurring. Any approved repairs shall be documented and photographed during the repair work and after completion of the repair. 5-155 (l) Deck Panel Rejection Criteria . Deck panels that exhibit any of the following conditions shall be rejected.
1.Any crack that has a transverse or diagonal orientation relative to the strand pattern and crosses more than one strand.
2.Any crack that is paralle l to a strand and is longer than 33% of the panel length.
3.Cracks that are shorter than 33% of the panel length and occur at more than 12% of the total number of strands in the panel.
4.Voids or honeycombed areas with exposed strands.
5.Any other re ason that the Structural Concrete Engineer determines could have an adverse impact on the structural integrity of the deck panel.
m.Finishing Riding Surfaces with No Asphalt Wearing Surface . All exposed riding surfaces not covered with an asphalt wearing surface shall be given a finish as specified on the approved shop drawings, or if not specified, in accordance with the requirements of Subsection 501.1 4.
n.Welding . All welding shall conform to the requirements of Subsection 506.10 .
o.Cold Weather Co ncrete . Cold weather concrete will be any concrete placed or cured when the ambient air temperature is expected to be below freezing at any point in time or below 40°F for an 8-hour continuous period. The requirements of Subsection 501.07(b) shall apply in addition to the requirements of Subsection 510.09 .
p.Marking . The date of manufacture, the production lot number, and the piece mark shall be clearly marked on each individual piece of prestressed concrete. The mark shall be in a location that will not be visible in the finished product. 510.0 9 CURING .
a.General Requirements . All curing methods for prestressed concrete shall be subject to the Structural Concrete Engineer’s approval. The fabricator shall submit complete details of the proposed meth ods for approval with the fabrication draw ings. The curing period for prestressed concrete is defined as wet curing for a minimum of 72 hours, to begin immediately following the completion of placing and finishing of the concrete. The following requirement s shall apply: 5-156 (1) The method of curing shall prevent the loss of moisture throughout the cure period. Except where modified herein, prestressed concrete structure components shall be cured by water curing, by wetted burlap covered with white polyethylene sheeting, or by burlap -white polyethylene sheeting (burlene) as specified in Subsection 501.1 5.
2.When a curing enclosure is used, free water shall be evident and the relative humidity within the enclosure shall exceed 90% throughout the dur ation of the curing period. A curing enclosure is considered any means of moisture -retention that allows air to contact the surface of the piece.
3.The concrete’s strength shall be determined by test specimens cured with the product they represent, or by specimens match -cured in an approved match -curing system.
4.Wet curing shall continue until 80% of the 28 -day design strength is achieved, but shall be no less than 72 hours in duration.
5.Curing by the approved method shall continue u ninterrupted until the start of de -tensioning operations. De -tensioning shall be accomplished while the product is still warm. Wet curing shall be resumed upon removal of the product from the forms.
b.Curing Temperatures .
1.The controlling temperatures for concrete curing shall be those actually achieved within the concrete elements, and not the ambient temperatures of the curing area unless specifically stated as such.
2.The internal temperature of the prestressed concrete shall be raised to at least 68°F within the first 12 hours of the curing period, and shall be maintained at or above 68°F for the remainder of the entire curing period.
3.The internal temperature of curing concrete shall be monitored using sacrificial thermocouples placed as near as practicable to the center of mass of the finished piece. In addition, the temperature within the curing enclosure shall be monitored using strategically placed temperature sensors so that the reported temperatures accurately represent the curing conditi ons. The requirement for temperature monitoring may be waived by the Structural Concrete Engineer if the concrete is not subject to accelerated curing and ambient temperatures are expected to be well in excess of 40°F throughout the duration of production. 5-157 (c) Accelerated Curing . Accelerated curing procedures may be employed in lieu of the standard 72 - hour curing procedure described in Subsection 510.09(a) , in accordance with the requirements of PCI MNL -116, Section 4.19 and the following:
1.The initial time of set is defined in AASHTO T 197 and ASTM C403 as the time it takes for fresh concrete to attain a compressive strength of 500 psi. Testing to determine the time of set shall be done when the concrete temperature is within ± 5°F of the anticipated concrete placement temperature. Alternately, time of set may be found by taking a minimum of three different concrete temperatures at intervals of approximately 10°F, entering that data on a graph, and then drawing a best -fit smooth curve line through the three data points. This graph will be used to determine the time of set for the anticipated concrete placement temperature, rounded up to the nearest half hour.
2.Immediately upon completing placement of the concrete for each prestressed conc rete structure component, an enclosure that is suitable for containing live low -pressure steam or heat shall be placed over the forms. The fabricator shall make these enclosures available for inspection prior to casting.
3.When low -pressure steam heating methods are used for accelerated curing, precautions shall be taken to prevent the live steam from being directed on the concrete or forms in such a way as to cause damage from localized high temperatures.
4.When radiant heat is used for accelerated cur ing, all exposed concrete surfaces shall be covered with plastic sheeting. Radiant heat may be applied by means of circulation pipes containing steam, hot oil, or hot water, or by electric heating elements.
5.While waiting for the initial set to take pla ce, the temperature within the concrete may be increased at a maximum rate of 10°F per hour. However, the temperature within the concrete shall not be more than 40°F higher than the initial concrete placement temperature or more than 104°F, whichever is le ss. Following the initial set, the internal concrete temperature shall be increased at a rate of not more than 40°F per hour until the desired curing temperature is reached. The maximum internal concrete temperature shall not exceed 160°F. The maximum diff erential between the curing enclosure temperature and internal concrete temperature shall not exceed 40°F. The selected curing enclosure temperature range shall be as approved on the fabrication draw ings. 5-158 The accelerated curing cycle shall be considered c omplete when the method of supplying heat is stopped or the concrete temperature drops below 120°F. Two concrete cylinders shall be tested immediately upon completion of the accelerated cure cycle. The maximum cooling rate from the sustained accelerated curing temperature shall be 50°F per hour. Cooling at this rate shall continue until the concrete temperature is 40°F or less above the ambient temperature outside the curing enclosure.
6.Prestressed concrete that has not attained 80% of its 28-day design strength shall be additionally wet -cured until this strength threshold is met. If the precast concrete has attained 80% of its 28 -day strength during the accelerated curing cycle, no further curing will be required.
d.Conditioning . Followin g the completion of the chosen curing method, precast elements that are to be exposed to cold weather conditions as defined in Subsection 5 10.08(o) shall be allowed to cool and dry in an environment of at least 40°F for 24 hours to prior to exposure to cold weather conditions. For pieces cast outdoors in cold weather ambient conditions, all requirements of Subsection 501. 07(b) shall apply.
e.Temperature Recording . The fabricator shall install one automatic temperature recorder for every 100 feet of production length. The Structural Concrete Engineer may require that additional temperature recorders be installed if it is determined that the one per 100 feet of production length spacing does not allow for adequate monitoring of the curing conditions. Temperatures recorded on the data logs shall be used to determine whether the prestressed concrete structure components have been cured in accordance with th e specifications and the approved fabrication draw ings. The recorder shall record, at intervals not to exceed 15 minutes, the temperature of the air surrounding the piece as well as the internal concrete temperature. Temperature recording shall continue un til completion of the chosen curing method. Each recorder’s data log shall indicate the casting bed, the date of casting, the start and finish times of record, and the mark number of the prestressed concrete structure component being cured. At the completi on of the temperature recording period, the data logs shall be given to the Agency representative. Recorder accuracy shall be certified at least once every 12 months, and the certificate displayed with the recorder. Calibration and certification shall be p erformed by either the manufacturer, the supplier, or an independent laborat ory. Random temperature checks of each recorder may be made by an Agency representative. 5-159 510.1 0 HANDLING , STORAGE , AND SHIPPING . Handling and installation of prestressed members shall be performed with members in an upright position and with points of dunnage support and direction of lifting reactions as specified in the approved lifting calculations. Prestressed concrete shall be handled, stored, and shipped i n such a manner as to minimize chipping, cracks, fractures, discoloration, and excessive bending stresses. Units damaged by handling, storage, or shipping shall be replaced at the Contractor’s expense. Prior to shipment of any members, all NCRs shall be re solved and all required testing shall demonstrate that the design requirements have been met. 510.1 1 INSTALLATION .
a.Prestressed Concrete Members .
1.Methods, Equipment and Erection . Cranes, lifting devices, and other equipment for all prestressed concrete member erection shall be of adequate design and capacity to safely erect, align, and secure all members and components in their final positions without damage. The Contractor is solely responsible for the methods and equipment employed for the erection of the prestressed concrete member. Construction drawings for prestressed concrete member erection shall be submitted in accordance with the requirements of Subsection 105.06 . The erection plan shall include the methods and sequence of pr estressed concrete member erection, temporary bracing requirements, the equipment to be used for the erection, and the necessary computations to demonstrate that all of the erection equipment has adequate capacity for the work to be performed. The erection plan shall also include provisions for all stages of construction, including temporary stoppages. When the fabricator -designed lifting hooks will be used by the Contractor, computations indicating the magnitude of stress in the segments during erection ar e not required, unless otherwise ordered by the Engineer. The prestressed concrete members may be used for support of equipment prior to placement of the deck only with written permission of the Engineer. The proposed use of the prestressed members for support of equipment shall be detailed in the erection plan. Submittal of the erection plan is for documentation purposes only and shall in no way be construed as approval of the proposed method of erection. The Contractor shall follow the erection plan as submitted. 5-160 (2) Initial Post -tensioning . The Contractor shall insert post -tensioning strands in the conduits and tension them to 3.0 kips.
3.Grout . Grout shall be placed in accordance with the requirements of Subsection 510.12 .
4.Fairing Surfaces . This work shall consist of placing grout between prestressed members as required for fairing out any unevenness between adjacent units. Type IV mortar shall be used, and grout placement shall occur at the same time mortar is placed to fill shear keys between members and in accordance with the requirements of Subsection 510.12 . The mortar shall be placed to eliminate unevenness, forming a smooth surface f rom the higher beam edges to the lower surface. The finished surface shall be feathered smoothly and be free of depressions or sharp edges.
5.Final Post -Tensioning . Strands shall be post -tensioned in accordance with the requirements of Subsection 510.13 .
b.Prestressed Deck Panels .
1.Prestressed deck panels shall be installed as shown on the Plans. The temporary supports shall be attached to the top of the flange of the girder with an adhesive, approved by the Engineer, in accordance with the manufacturer’s recommendations. The temporary supports shall be cut in the field to the required height after the blocking depth has been determined. The bottom of the panels shall be a minimum of 1 inch above the top of the top flange of the girder.
2.Prestressed deck panels shall not be used to support heavy loads, such as additional deck panels, until the top slab is cast and cured. Construction loads on individual panels shall be uniformly applied and shall not exceed an average loading of 40 pounds p er square foot.
3.After the prestressed deck panels have been placed on temporary supports, the area under the ends of the panels and over the girder flanges up to the bottom of the panels shall be completely filled with the material specified on the Plans. Temporary supports and grout dams for prestressed deck panels shall consist of continuous strips of high density, extruded polystyrene insulation board with a minimum compressive strength of 60 psi. 5-161 If leveling screws are used, polyethylene foam with a density of 1.7 pcf shall be employed as a grout dam. Prior to placement of the cast -in-place deck, the concrete shall be wet cured until a minimum of 85% of f′ c is attained by the average strength of two field -cured concrete cylinders. The leveling screws shall be completely removed and the holes filled with grout prior to the placement of deck concrete.
4.Prior to placing the deck concrete, any laitance or other contaminates that would interfere with full bond to the panels shall be removed by an approved method. 510.1 2 GROUT .
a.Surface Preparation . The fabricator shall ensure that surfaces to be grouted are clean, oil -free, and roughened in a ccordance with the Plans. The surface to be grouted shall be thoroughly wetted, yet free of all standing water. Shear keys shall be saturated surface dry prior to grouting.
b.Grout Mixes . Grout shall be used to fill shear keys, transverse tie anchor recesses, and dowel holes, level screw voids, and for fairing joints as detailed in the Contract or as ordered by the Engineer. Grout shall be Type IV mortar in accordance with Subsection 707.0 1(e)(1) . Additional aggregates shall not be added to the material during field mixing. Ready mixed mortar in accordance with Subsection 707.01(e)(2) may be substituted with written permission of the Engineer. Placement of ready mixed mortar shall be complete within 90 minutes of the time of batching. The Co ntractor shall submit a proposed grouting procedure to the Engineer for their review and approval. The proposed grouting procedure shall include the required equipment, workforce, manufacturer’s product data sheet for prepackaged mortar or the approved mix design of the ready mixed mortar when approved, placement rate, batch size, and all necessary details to explain how the grouted element will be placed in accordance with specification and manufacturer recommendations, as applicable, without air voids or cold joints. Post-tensioning may occur when a field cured sample demonstrates conformance with post - tensioning strength requirements specified in the Contract, as determined in accordance with ASTM C109 . Three cubes shall constitute a single sample.
c.Placing Grout . The grout shall be mixed using a mechanical mixer according to the manufacturer’s recommendations and shall be readily pourable so that it completely fills the shape of the shear keys or holes, depending on the product being installed. The placement of t he grout for each shear key shall be continuous. The grouting of each shear key shall be completed in its entirety within a single working day . 5-162 (d) Curing Grout . In the absence of manufacturer curing recommendations, all exposed grout shall be cured for not less than 3 days by the wetted burlap method in accordance with the requirements of Subsection 501 .15. Curing shall commence immediately following completion of grouting of individual shear keys. 510.1 3 POST -TENSIONING . Post -tensioning strands shall not be bonded to the concrete and shall be protected against corrosion as specified in the Contract. Post-tensioning of strands shall not commence until a minimum compressive strength of 1,500 psi has been attained in the grout, when tested in accord ance with the requirements of Subsection 510.12(b) . If the design strength is met prior to completion of the required curing, the grout cure shall be maintained during the post -tensioning operation. Strands shall be stressed in the following sequence:
a.Before grouting, the strands shall be pulled with a maximum force of 3.0 kips.
b.After the grout has attained the required strength, the strands shall be pulled to the final design tension. Stressing shall begin by pulling the inner -most strands first, then proceeding symmetrically towards the member ’s ends.
c.The inner strands shall be rechecked to ensure the strands still have the design tension. In the case where the Plans call for top and bottom strands, the sequence shall be followed using an initial pull of 15.0 kips, top and bottom, followed by a sequence using the final design tension. No loading of elements shall be allowed until post -tensioning is completed. 510.1 4 METHO D OF MEASUREMENT . The quantities of Prestressed Concrete Box Beams, Prestressed Concrete Voided Slabs, Prestressed Concrete Girders, Prestressed Concrete Solid Slabs and Prestressed Concrete NEXT D Beams to be measured for payment will be the number of linear feet of the types and sizes of prestressed concrete members used in the complete and accepted work. The quantity of Grouting Shear Keys to be measured for payment will be the number of linear feet of grouted shear keys in the complete and accepted work. The quantity o f Prestressed Concrete Deck Panels to be measured for payment will be the number of square feet of prestressed concrete deck panels used in the complete and accepted work. 5-163 510.1 5 BASIS OF PAYMENT . The accepted quantities of Prestressed Concrete Box Beams, Prestressed Concrete Voided Slabs, Prestressed Concrete Girders, Prestressed Concrete Solid Slabs , and Prestressed Concrete NEXT D Beams will be paid for at the Contract unit price per linear foot for the types and sizes of prestressed concrete members specified. The accepted quantity of Prestressed Concrete Deck Panels will be paid for at the Contract unit price per square foot. Payment will be full compensation for detailing, fabricating, repairing, sandblasting, quality control testing, transporting, handling, and installing the materials specified, including the concrete, reinforcement, prestressing steel, transverse ties, encl osures for prestressing steel, anchorages, mortar, and anchor rods. Payment will be full compensation for any other material contained within or attached to the members, for furnishing and implementing the erection plans, and for furnishing all labor, tool s, equipment, and incidentals necessary to complete the work. The Engineer may authorize partial payments in the following manner:
a.A maximum of 25% of the Contract bid amount may be paid when the fabrication draw ings have been approv ed by the Agency .
b.In accordance with the requirements of Subsection 106.09 , stockpile payment may be authorized when the prestressed elements have met the requirements of Subsection 540.09 for shipping.
c.After completion and acceptance of all work under this section , 100% of the quantity will be paid. The accepted quantity of Grouting Shear Keys will be paid for at the Contract unit price per linear foot. Payment will be full compensation for providing all materials and performing the work specified herein, and for furnishing all labor, tools, equipment, and incidentals necessary to complete the work. Any other grouting work, such as fairing out unevenness between adjacent units and filling leveling screw holes, transverse anchor recesses, and dowel holes, will be considered incidental to the work for prestressed concrete members. 5-164 Payment will be made under: Pay Item Pay Unit
510.21 00 Prestressed Concrete Box Beams ................................ .............................. Linear Foot
510.22 00 Prestressed Concrete Voided Slabs ................................ ........................... Linear Foot
510.23 00 Prestressed Concrete Girders ................................ ................................ ....Linear Foot
510.24 00 Grouting Shear Keys ................................ ................................ ................. Linear Foot
510.25 00 Prestressed Concrete Solid Slabs ................................ .............................. Linear Foot
510.26 00 Prestressed Concrete NEXT D Beams ................................ ...................... Linear Foot
510.4000 Prestressed Concrete Deck Panels ................................ ............................ Square Foot 5-165 SECTIO N 511 – REMOVAL, CONTAINMENT, AND DISPOSAL OF LEAD PAINT 511.0 1 DESCRIPTION . This work shall consist of the washing of the existing lead paint coated surfaces, the removal of existing lead paint and grease rustproofing compounds, as well as the containment, collection, temporary storage, transportation, and disposal of the resulti ng waste. Waste requiring containment and control includes, but is not limited to, old paint, spent abrasives, corrosion products, mill scale, dirt, dust, grease, oil, salts, solvents, and water used for cleaning the surface of existing lead coatings. Are as of paint removal operations shall be as indicated on the Plans. 511.0 2 GENERAL REQUIREMENTS . The existing coatings are assumed to contain lead and other toxic metals, regardless of any test results. All removal activities will be performed accordingl y. This specification provides the requirements for containment and for the protection of the public and the environment from exposure to harmful levels of toxic metals that may be present in the paint being removed or repaired. The Contractor shall take reasonable and appropriate precautions to protect the public from the inhalation or ingestion of dust or debris from the operations, and is responsible for the clean -up of all spills, releases, or emissions of waste at no additional cost to the Agency. The Contractor shall comply with the requirements of this specification and all applicable federal, state, and local laws, codes, and regulations. These include, but are not limited to, the regulations of the U.S. Environmental Protection Agency, Vermont Occu pational Safety and Health Administration (VOSHA) , Vermont Department of Health, and the Vermont Agency of Natural Resources. The Contractor shall comply with all applicable regulations even if the regulation is not specifically referenced herein. If a federal, state, or local regulation is found to be more restrictive than the requirements of this specification, the more restrictive requirements shall prevail as determined by the Engineer. 511.0 3 PROJEC T CLASSIFICATION . The removal, containment and disposal of lead paint will be classified as either a Type I or a Type II project as follows:
a.Type I . Type I projects shall consist of work to remove all paint from a substantial portion of the existing structure, or to remove the paint from large, con tiguous areas of a portion of a structure. Examples of such work would be projects where all or some of the main girders were completely stripped of paint. Often, paint removal and repainting the structure will be a primary goal of a Type I project. Type I projects can usually be expected to require a full external containment system.
Source: Vermont Standard Specifications for Construction, 2024 Edition. Pages 555–578 of 1,380.