5-249 SECTIO N 540 – PRECAS T CONCRETE 540.0 1 DESCRIPTION . This work shall consist of manufacturing, transporting, and erecting precast concrete structure components. 540.0 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 Mechanical Splices for Bar Reinforcement ................................ ............................... 713.02 Welded Wire Reinforcement ................................ ................................ ..................... 713.0 3 Prestressing Strand and Post -Tensioning 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 Admixtures ................................ ................................ ........................... 725.02(i) Water -Reducing and Accelerating Admixtures ................................ ......................... 725.02(j) Specific Performance Admixtures ................................ ................................ ............. 725.02(k) Mineral Admixtures ................................ ................................ ................................ ...725.0 3 Waterproofing Membrane System, Type III ................................ .............................. 726.08(c) Polystyrene Insulation Board ................................ ................................ ..................... 735.01 5-250 Blanket Insulation Material ................................ ................................ ........................ 735.02 Pipe Insulation ................................ ................................ ................................ ........... 740.0 6 Water ................................ ................................ ................................ .......................... 745.01 Concrete Repair Material , Type I ................................ ................................ .............. 780.0 1(a) Concrete Repair Material, Type II ................................ ................................ ............. 780.01(b) Bearing pads for structures shall meet the requirements of Section 731 . 540.0 3 GENERA L FABRICATIO N REQUIREMENTS .
a.General Requirements . The manufacture of the precast units shall be in accordance with PCI MNL - 116 and PCI MNL -135, except as modified in this section , or with the NPC A Quality Control Manual for Precast Plants.
b.Qualification . Precast concrete shall be manufactured in a plant that has been certified by either PCI under its plant certification program for precast concrete or by the NPCA plant certification program. Precast concrete shall be manufactured in a plant that maintain s a quality control laborat ory 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 tes ting machine shall be power operated and capable of applying the load continuously rather than intermittently, and without shock.
c.Quality Control . The fabricator shall demonstrate a level of quality control testing that satisfies the Agency as to its a bility and commitment to produce precast 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 determinatio ns of the concrete. These tests shall be performed at regular and suitable intervals as specified in the Materials Sampling Manual and actively used to maintain the quality of the concrete within the specified requirements. The fabricator shall have a plan t specific quality control plan approved by the Agency prior to the beginning of any fabrication activities. 5-251 540.0 4 SUBMITTALS . As soon as practical after award of the Contract, all required information shall be prepared and submitted. A complete copy of the structural design calculations for the precast concrete shall be submitted as construction draw ings in accordance with the requirements of Subsection 105.06 . The design calculations shall substantiate that the proposed precast concrete satisfies the design parameters of the Contract. The design calculations shall include a load rating for superstructures with a span length greater than or equal to twenty feet, measured along the roadway centerline. For all other superstructures, the design vehicle shall be clearly noted in the calculations. Where applicable, superstructures shall be load rated for all the vehicle configurations noted in the load rating section of the VTrans Structures Design Manual . The design calculations shall also include any general or construction notes required for the fabrication and construction of the precast concrete. The applicab le design code will be the AASHTO LRFD Bridge Design Specifications unless otherwise indicated in the Contract. Fabrication drawings , also referred to in the precast industry as production drawings or shop drawings , for the precast concrete shall be submitted in accordance with the requirements of Subsection 105.06 , with an additional copy provided to the Structural Concrete Engineer. Fabrication drawings shall include such detail as needed to fully describe the inte nded as -built condition of the precast elements including any connections between precast elements or existing structures and materials. In addition to the requirements for fabrication draw ings in Subsection 105.06 , the following shall be included:
a.Concrete Mix Design . The concrete mix design shall include, but not be limited to, the following components:
1.Batch weights specifying dry or saturated surface dry.
2.Material names and sources .
3.Aggregate properties and date tested. Aggregates shall be tested on an annual basis, at a minimum for absorption and specific gravity per the requirements of AASHTO T 84 and AASHTO T 85 and unit weight per the requirements of AASHTO T 19 .
4.Chemical and physical properties of cementitious ma terial.
5.Admixture names and sources. 5-252 (6) Lab data that shall include, but not be limited to, the following items:
a.The maximum water/cementitious materials (W/CM) ratio that will be allowed during production, including water contributed to hydration 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.Slump/spread minimum a nd maximum, 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 SCC mix, the difference between the J -ring test (ASTM C1621 ), and the spread test (ASTM C1611 ), shall be two 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. T he concrete shall not demonstrate segregation at the minimum or maximum slump/spread.
c.Air content as tested in accordance with the requirements of AASTHO T 152 .
d.Temperature as tested in accordance with ASTM C1064.
e.Cylinder compression results obta ined in accordance with the requirements of AASHTO T 22 for early breaks, design strength, and the 28 -day standard cure as defined in AASHTO R 100 . The type of cure shall be listed 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 p rior 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 laboratory. 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. 5-253 g. The alkali -silica reactivity (ASR) of each ty pe 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 requirements of ASTM C1567 . The Contractor may elec t 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 data that meets the requirements of AASHTO T 160 shall be performed by an independent AASHTO re:source qualified laborat ory accredited in testing in accordance with 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.
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.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 shall include, but not be limited to, specific gravity, unit weight, and absorption. Aggregate property values wil l be valid for 14 months from the date tested.
c.The mix design shall be accompanied by the previously completed and accepted test mix data and any applicable updated test information. New mix designs and mix designs that were approved more than 36 month s ago shall have new testing completed to be submitted for approval. The proposed concrete mix design, including performance history and all requests for variance from the 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. 5-254 (b) Dimensions and Tolerances . The dimensions and tolerances of the sections to be fabricated.
c.Steel Locations . The location of reinforcing steel, welded wire fabric, mechanical bar connectors, and inserts.
d.Surface Finish . The type of surface finish and how the finish will be obtained.
e.Curing Method . The curing method, detailing the sequence and duration in accordance with the requirements of Subsection 540.08 .
f.Minimum Required Strength . The minimum required concrete strength for form removal.
g.Lifting Attachments . The design of the lifting attachments, including the minimum required concrete strength to allow lifting , with 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 is met.
h.Logistics . A description of the transportation, handling, and storage details.
i.Installation and Grouting . A description of the installation and grouting procedures.
j.Quality Control . A description of the 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 submittals. 540.0 5 CONCRETE .
a.Batch Plants . Batch plant equipment, materials, and batching procedures shall conform to the subsections of Section 501 listed in Table 540.05A . 5-255 TABLE 540.05A – 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 precast concrete shall conform to the following requirements:
1.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 unac ceptable 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 c ement 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 production shall not exceed the maximum W/CM ratio determined in Subsection 540.04(a)(6)a.
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 b etween 50°F and 85°F, as tested in accordance with the requirements of AASHTO T 309 . 5-256 (5) The concrete shall not demonstrate segregation at any time. If the mix fails to remain within the minimum/maximum slump or spread submitted in the mix design, the loa d may be rejected. The visual stability index (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 with the piece they represent through the complete curing period. These cylinders shall meet the testing requirements of AASHTO T 277 and AASHTO T 358 and shall be kept with the piece they represent until collected by the Agency. Any admixture containing calcium chloride shall not be used. Only the cementitious combinations and sources from the approved mix design shall be used in the precast units required for any one structure, unless otherwise authorized by the Structural Concrete Engineer. 540.0 6 INSPECTION . Materials furnished and the work performed under Section 540 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 Eng ineer 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 facil ities and require suitable alternatives. 540.0 7 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 Structural 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 representative 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 draw ings and a complete anticipated production schedule for all components included in the fabrication drawings. 5-257 (b) Forming Members . Any defects or damage due to form work, stripping, or handling may be cause for rejection. Holes or cutouts for anchoring devices, diaphragm connections, openings for connection rods, recesses for grout holes for guardrail bolts, and any other rel ated details shown on the Plan s shall be provided for in the members.
c.Post-Tensioning Strands and Conduits . Each post -tensioning strand to be post -tensioned shall be encased in an approved conduit. Unless otherwise shown on the Plan s, the ratio of cros s-sectional area of the post tensioning strand 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 t he diameter of the bar. Conduit that has been crushed or has opened seams shall not be used. 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 Plan s. Bundling of conduits will not be permitted.
d.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 precast concrete units.
e.Placing Concrete . Concrete shall not be deposited in the forms until the Agency representative has approved placement of the reinforcement, conduits, and anchorages. The concrete shall be vibrated internally, exter nally, or a combination thereof to the required consolidation. When a vibrator is used with rebar with special coatings or made of non -metallic material or a 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. The vibrating shall be done with care and in such a manner to ensure that the following conditions are met:
1.The concrete is uniformly consolidated.
2.Displacement of or damage to reinforcement, inserts, conduits, and anchorages is avoided.
3.Acceptable finish surfaces are produced. 5-258 (f) Dimensional Tolerances . All dimensio nal tolerances shall be in accordance with PCI MNL -116 and PCI MNL -135, or with the NPCA Quality Control Manual for Precast Concrete, unless otherwise noted in the Contract or as approved by the Engineer.
g.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, honeycombing, chips, or spalls, which are 6 inches or less in the longest dimension, and that do not penetrate dee per than 1 inch into the concrete. Minor defects may be repaired using an approved standard repair proc edure as detailed in Subsection 540.07(g)(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 , at the discretion of the Structural Concrete Engineer. Major defects are anything beyond the scope of minor as described above. 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 their width, length, location, and frequency. At the Structural Concrete Engineer’s discretion, cracked members shall be repaired or replaced at the Contractor’s expense. Members with crack widths of 0.05 inch and greater will be rejected.
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 surf ace 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.Standard ized Repair Procedures . Standard ized repair procedures (SRPs) will document a prescribed procedure for repairing minor defects at the fabricator ’s facility. At a minimum the SRP shall detail the scope of defects for which that procedure is intended to be used, 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 example pictures of defects for which the procedure could be used, detailed example pictures of every step of the repair procedure, and pictures of an example completed repair. 5-259 Approval to use an SRP for any given defect is at the sole discretion 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 an SRP for 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) . At a minimum, the NCR shall detail what the defect is, including adequate pictures of the piece and defect, what caused it, the proposed repair, the procedure for carrying out the proposed repair, and a plan of action to prevent additional similar defects from occurring. Any approve d repairs shall be documented and photographed during the repair work and after completion of the repair. NCRs shall be submitted within 2 working day s of the discovery of the defect.
h.Welding . All welding shall conform to the requirements of Subsection 506.10 .
i.Cold Weather Conditions . Cold weather concrete will be any concrete placed or cured in ambient conditions 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 540.08 .
j.Marking . The date of manufacture, the production lot number and the piece mark shall be clearly marked on each individual piece of precast concrete. The mark shall be in a location tha t will not be visible in the finished product.
k.Form Removal . Unless otherwise specified, form removal shall be permitted only after the strength required and approved in Subsection 540.04(f) is achieved as specified in the Materials Sampling Manual .
540.08 Curing .
a.General Requirements . All curing methods for precast concrete shall be subject to the Structural Concrete Engineer’s approval. The fabricator shall submit with the fabrication draw ings complete details of the proposed methods for approval. The curing period for precast concre te is defined as a minimum of 72 hours of wet curing to begin immediately following completion of placing and finishing of the concrete. The following requirements shall apply: 5-260 (1) The method of curing shall prevent the loss of moisture throughout the curing period. Except where modified herein, precast concrete structure components shall be cured by either water curing, wetted burlap covered with white polyethylene sheeting, or white burlap -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 duration 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 strength of the product shall be determined by test specimens cured with the product they represent, or by specimens match -cured in an approved match -curing system. Wet curing shall be continued until 80% of the 28 -day design strength is achieved, but shall be no less than 72 hours in duration.
b.Curing Temperatures .
1.The controlling temperatures shall be those actually achieved within the concrete elements, not ambient temperatures of the curing area unless specifically stated as such.
2.The precast concret e shall be raised to an internal temperature of not less than 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 curing period.
3.The internal temperature of curing concrete shall be mon itored 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 temperature sensors placed carefully within the curing enclo sure in such a way that temperatures being measured accurately represent the curing conditions. The requirement for temperature monitoring may be waived by the Structural Concrete Engineer if the concrete is not subject to accelerated curing and ambient te mperatures are expected to be well above 40°F throughout the duration of production.
c.Accelerated Curing .
1.Accelerated curing procedures may be employed in lieu of the standard 72 -hour curing procedure described in Subsection 540.08(a) , in accordance with the requirements of PCI MNL -116, Section 4.19 and the following conditions: 5-261 a. The initial time of set is defined in AASHTO T 197 and ASTM C403 as the time it takes fresh concrete to reach a compressive strength of 500 psi. Testing to determine the time of set shall be done when the 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 precast concrete 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 prev ent 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 curing, all exposed concrete surfaces shall be covered with plastic sheeting. R adiant 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 place, the temperature within the concrete may be increased at a maximum rate o f 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 less. Following initial set, the internal concrete temperature shall increase at a rate not exceeding 40°F per hour until the desired curing temperature is reached. The maximum internal concrete temperature shall not exceed 160°F. The maximum differential between the curing enclosure temperature and internal concrete temperature sha ll not exceed 40°F. The selected curing enclosure temperature range shall be as approved on the fabrication draw ings. The accelerated curing cycle shall be considered complete when the method of supplying heat is stopped or the concrete temperature drops b elow 120°F. Two cylinders shall be tested immediately upon completion of the accelerated cure cycle. 5-262 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.Precast concrete that has not attained 80% of the 28 -day design strength shall be additionally wet cured until this strength threshold is met. If the precast concre te has attained 80% of the 28 -day strength during the accelerated curing cycle, no further curing will be required.
d.Conditionin g. Following the completion of the chosen curing method, precast elements that will then be exposed to cold weather conditions as defined in Subsection 540.07(i) shall be allowed 24 hours to cool and dry in an environment of at least 40°F 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 a minimum of one automatic temperature recorder per contiguous form group and common heat source, per day. The Structural Concrete Engineer may require that additional temperature recorders be installed if it is determined that one per day of production does not adequately monitor the curing conditions. 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 until completion of the chosen curing method. Each recorder’s data log shall indicate the casting bed, date of casting, time of start and finish of record, and the mark number of the precast concrete structure component being cured. At the completion of the temperature recording, the data logs shall be given to the Agency representative. Temperatures recorded on the data logs shall be used to determine whether the precast concrete structure components have been cured in accordance with the specifications and the approved fabrication draw ings. Recorder accuracy shall be certified at least once every 12 months, and the certificate displayed with the recorder. Calibration and certification shall be performed by either the manufacturer, the supplier, or an independent laborat ory. Random temperature checks of each recorder may be made by an Agency representative. 540.0 9 HANDLING , STORAGE , AND SHIPPING . All precast concrete shall be handled, stored, and shipped in 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 resolved. In addition, all required testing shall demonstrate the design requirements have been met. 5-263 540.1 0 INSTALLATION .
a.Methods, Equipment and Erection . Cranes, lifting devices, and other equipment for precast concrete structure 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 precast concrete structure components. Construction drawings for precast concrete structure component er ection shall be submitted in accordance with the requirements of Subsection 105.06 . The erection plan shall include the necessary computations to indicate the magnitude of stress in the units during erection and to demonstrate that all of the erection equi pment has adequate capacity for the work to be performed, and 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 are not required, unless otherwise ordered by the Engineer. 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.
b.Sheet Membrane Waterproofing . A reinforced asphalt, synthetic resin, or coal -tar based preformed sheet membrane shall be placed over the joints of precast concrete units in accordance with the Contract . All work performed shall be in accordance with the manufacturer’s recommendations . Membrane material shall meet the requirements of Subsection 726. 08(c). Waterproofing shall not be performed in wet weather or when the temperature is below 40°F, without the authorization of the Engineer. The concrete surfaces that are to be waterproofed shall be reasonably smooth and free from projections or holes and shall be cleaned of dust and loose material. The surfaces shall be visibly dry prior to and during application of the membrane system. 540.1 1 GROUT .
a.Surface Preparation . The fabricator shall ensure that surfaces to be grouted are clean, oil -free, and roughened in accordance with the Plan s. 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. 5-264 (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 morta r 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 Contractor shall submit a proposed grouting procedure to the Engineer for their review and approva l. 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 d etails 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 pos t- 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 shall be continuous. The grouting of each shear key shall be completed in its entirety within a single working day . Grout shall be placed between precast concrete structure components as required for fairing out any unevenness between adjacent com ponents. Type IV mortar shall be used. The mortar shall be placed to the thickness necessary to eliminate unevenness, forming a smooth surface from the higher edges to the lower surface. The finished surface shall be feathered smoothly and be free of depre ssions or sharp edges.
d.Curing Grout . In the absence of manufacturer curing recommendations, all exposed grout shall be cured for not less than three days by the wetted burlap method in accordance with the requirements of Section 501 . Curing shall comme nce as soon as practical after grout placement. 540.1 2 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 accordance with the requirements of Subsection 540.11(b) . If the design strength is met prior to completion of th e required curing, the grout cure shall be maintained during the post -tensioning operation. 5-265 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 Plan s call for top and bottom strands, the sequence shall be followed using an ini tial 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. 540.1 3 METHO D OF MEASUREMENT . The quantity of Precast Concrete Structure of the type and size specified to be measured for payment will be on a lump sum basis in the complete and accepted work . The lump sum will include all of the precast concrete structure components for each locati on specified in the Contract. The quantity of Precast Concrete Deck Panels to be measured for payment will be the number of square feet of precast concrete deck panels used in the complete and accepted work. 540.1 4 BASIS OF PAYMENT . The accepted quantity of Precast Concrete Structure of the type and size specified will be paid for at the Contract lump sum price. The accepted quantity of Precast Concrete Deck Panels will be paid for at the Contract unit price per square foot. Payment will be full compensation for designing, detailing, fabricating, repairing, transporting, handling, and erecting the materials specified, for furnishing and implementing the erection plan, and for furnishing all labor, tools, equipment, and incidentals neces sary 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 approved by the Agency .
b.In accordance with Subsection 1 06.09 , stockpile payment may be authorized when the precast elements have met the requirements of Section 540.09 for shipping.
c.After completion and acceptance of all work under this section , 100% of the quantity will be paid. 5-266 Furnishing and placing preformed sheet membrane waterproofing, including primer, mastic, polyurethane membrane sealant, and surface preparation, will be considered incidental to Precast Concrete Structure. Any grouting work, such as fairing out unevenness between adjacent precast concrete structure components and filling leveling screw holes, shear keys, transverse anchor recesses, and dowel holes, will be considered incidental to the work for Precast Concre te Structure. Payment will be made under: Pay Item Pay Unit
540.10 00 Precast Concrete Structure ................................ ................................ ........ Lump Sum
540.2000 Precast Concrete Deck Panels ................................ ................................ ...Square Foot 5-267 SECTION 541 – STRUCTURAL CONCRETE
541.01 DESCRIPTION . This work shall consist of furnishing and placing Portland cement concrete for
structures and incidental construction. The Portland cement concrete may consist of a homogeneous mixture of Portland cement, fine aggregate, coarse aggregate, water, admixtures, and pozzolans, proportioned and mixed according to these specifications.
541.02 MATERIALS . Materials shall meet the requirements of the following subsections:
Portland Cement ................................ ................................ ................................ ......... 701.02 Portland -Pozzolan Cement ................................ ................................ ......................... 701.04 Portland -Limestone Cement ................................ ................................ ...................... 701.05 Portland Blast -Furnace Slag Cement ................................ ................................ ......... 701.06 Ternary Blended Cement ................................ ................................ ........................... 701.07 Fine Aggregate for Concrete ................................ ................................ ...................... 704.01 Coarse Aggrega te for Concrete ................................ ................................ .................. 704.02 Lightweight Coarse Aggregate for Concrete ................................ ............................. 704.14 Lightweight Fine Aggregate for Concrete ................................ ................................ .704.19 Mortar, Type I ................................ ................................ ................................ ............ 707.01 (b) Mortar, Type IV ................................ ................................ ................................ ......... 707.0 1(e) Preformed Joint Filler, Cork, and Asphalt -Treated Felt ................................ ............ 707.0 6 Polyvinyl Chloride (PVC) Waterstop ................................ ................................ ........ 707.08 Concrete Bonding Systems ................................ ................................ ........................ 707.1 4 Steel for Corrugated Metal Forms ................................ ................................ ............. 715.03 Epoxy Bonding Systems ................................ ................................ ............................ 719.01 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 Admixtures ................................ ................................ ........................... 725.02(i) Water -Reducing and Accele rating Admixtures ................................ ......................... 725.02(j) Specific Performance Admixtures ................................ ................................ ............. 725.02(k) Anti-Washout Admixtures ................................ ................................ ......................... 725.02(l) Pozzolans ................................ ................................ ................................ ................... 725.03(a) Silica Fume ................................ ................................ ................................ ................ 725.03(b) Ground Granulated Blast -Furnace Slag (GGBFS) ................................ .................... 725.03(c)
Source: Vermont Standard Specifications for Construction, 2024 Edition. Pages 663–680 of 1,380.