1076 -5 ASSEMBLED PRODUCTS Completely seal all edges of tightly contacting surfaces by welding before galvanizing. Galvanize assembled steel products in accordance with AASHTO M 111. 1076 -6 SHEETS Galvanize iron or steel sheets in accordance with ASTM A653. 1076 -7 REPAIR OF GALVANIZING Repair galvanized surfaces that are abraded or damaged at any time after the application of zinc coating. Surfaces to be repaired shall be clean, dry and free of oil, grease, pre -existing paint, corrosion and rust. Surface to be repaired sha ll be blast- cleaned to SSPC -SP 10 ( Near-White Metal ). Where circumstances do not allow blast or power tool cleaning to be used, then hand tools may be used. Cleaning shall meet SSPC -SP 2, the removal of loose rust, mil scale or paint to the degree specified, by hand chipping, scrapping, sanding and wire -brushing. Surface preparation shall extend into the undamaged galvanized coating. Spray using a non -aerosol spray, or brush - apply the paint to the cleaned areas with 2 coats of organic zinc repair paint meeting Article 15 1080 -7. Ensure that the total thickness of the 2 coats is not less than 3 dry mils. Allow adequate curing time before subjecting repaired items to service conditions in accordance with the manufacturer’s printed instructions. Application co nditions shall be 40°F Air/Steel temperature and rising, steel temperature shall be 5°F above the dew point and relative humidity shall be 85% or less. Follow paint manufacturers recommendation if more restrictive than above requirements. Follow paint manufacturers written instructions on storage temperatures, mixing application, continuous agitation and pot life. No thinners are to be used when applying organic zinc repair paint by brush or roller. Instead of repairing by painting with organic zinc repair paint, other methods of repairing galvanized surfaces that are abraded or damaged are allowed provided the proposed method is acceptable to the Engineer. Excessive damage to galvanized surfaces as determined by the Engineer is cause for rejection. Replace or re -galvanize rejected galvanized material. PRECAST CONCRETE UNITS -1 GENERAL Use precast concrete units that is NCDOT approved as found on the Department’s approved producer/supplier list. The Department will remove a manufacturer of precast concrete units from this producer/supplier list if the monitoring efforts indicated that non -specification material is being provided or test procedures are not being followed. This section covers the materials for and the production of precast reinforced concrete units produced in accordance with the contract. Where precast reinforced concrete circular manhole sections are used, they shall meet AASHTO M 199.
Producers of precast concrete members are required to establish proof of their competency and responsibility in accordance with the National Precast Concrete Association (NPCA) or American Concrete Pipe Association (ACPA) Certification Programs to perform work for the NCDOT . Certification of the manufacturing plant under either NPCA or ACPA program and submission of proof of certification to the State Materials Engineer is required before beginning fabrication. Maintain certification at all times while work is being performed for the Department. Submit proof of certification following each NCPA or
ACPA audit to the State Materials Engineer for continued qualification. These same requirements apply to producers subcontracting work from the producer dire ctly employed by the Contractor. All producers shall be listed as an approved producer/supplier before beginning any work for the Department. -2 PLAN REQUIREMENTS The plans for precast units will be furnished by the Department in the Roadway Standard Drawings or details shown in the project plans. When the Department does not make precast plans available and the Contractor chooses to precast, submit drawings to the Engineer for the items proposed to precast. Submit one complete set of drawings for review, at least 40 calendar days before beginning production. After acceptance, submit a complete set of drawings. Acceptance by the Engineer of contractor drawings will not be considered as relieving the Contractor of any responsibility for precast units. When precast units are load bearing and require structure design, have the plans prepared and certified by an engineer licensed by the State of North Carolina. Contractor fur nished drawings shall show complete design, installation and construction information in such detail as to enable the Engineer to determine the adequacy of the proposed units for the intended use. Contractor drawings shall include details of steel reinfor cement size, weight and placement and a schedule that lists the size and type of precast units at each location where the precast units are to be used. Produce precast units in accordance with the approved drawings. -3 MATERIALS Refer to Division 10. Item Section Air Entraining Agent 1024 -3 Chemical Admixtures 1024 -3 Coarse Aggregate 1014 -2 Curing Materials 1026 Fine Aggregate 1014 -1 Fly Ash 1024 -5 Ground Granulated Blast Furnace Slag 1024 -6 Miscellaneous Metals 1074 Portland Cement 1024 -1 Reinforcing Steel 1070 Silica Fume 1024 -7 Blended Cement 1024 -1 Water 1024 -4 -4 INSPECTION The Department reserves the right to place a duly authorized inspector in the plant at any time work related to the production of units for the Department is being performed. Notify the Engineer at least 15 business days in advance when such work is scheduled to begin. Provide an office area for the inspector of at least 50 sf with desk, chair, telephone, facilities for proper heating and cooling, adequate lightning , electrical outlets and internet access . Acceptance of precast units will be on the basis o f tests of materials, compression tests on concrete cylinders and inspection of the finished units, including amount and placement of steel reinforcement, to determine their conformance with the approved dimensions and design and their freedom from defect. The inspector will have the authority to reject any or all units not manufactured in accordance with these specifications. Any unit found to be defective in any manner at any time will be rejected and replaced by an acceptable unit or repaired in a manner approved by the Engineer.
Store all Department units in a separate area on the yard. Store all units on a solid, unyielding foundation free of standing water or in a manner directed by the Engineer. Do not stack units before inspection. Provi de access to all surfaces of units so the plant inspector has the opportunity to properly inspect the units before approval. The provided access should allow room for inspection personnel to safely and freely move between and around units. Do not stack a bove 6 feet off the ground.
Do not transport units away from the casting yard until the concrete has reached the minimum required 28 day compressive strength and a period of at least 5 days elapses after casting, unless otherwise permitted by the Engineer. Do not transport any unit from the plant to the job site before the approval of that unit by the plant inspector. Such approval will be indicated by the compliance with the Department’s RFID tag/label tagging policy in accordance with Section 1030 and verified product approval as noted by an authorized Field Inspection Report ( FIR) or NCDOT alternate ID . -5 PORTLAND CEMENT CONCRETE
Portland cement concrete is composed of Portland cement, coarse aggregate (#67 or 78M), fine aggregate, water and unless otherwise permitted by the Engineer, an air entraining agent. If other cementitious materials and/or chemical admixtures are u sed, use these materials in the proper proportions to obtain the optimum effect. Do not use calcium chloride or other admixtures containing calcium chloride. Supply concrete that develops a minimum compressive strength as shown in Table 1077- 1 unless other strengths are designated on the approved drawings. When required, air entrain concrete to provide an air content of 5% ± 2%. Supply concrete with a maximum slump of 3.5 inches unless a high range water reducer (super plasticizer) is approved by the Engineer. Supply concrete with a maximum slump of 3.5 inches. A slump of 8 inches is permitted only when obtained with the use of an approved high range water reducer . As an option, reduce the cement content of the mix design by up to 3 0% and replace with fly ash at a rate of 1 lb. of fly ash for each pound of cement replaced or reduce the cement content up to 50% and replace with blast furnace slag on a pound for pound basis. Submit proposed concrete mix designs in terms of saturated surface dry weights on Materials and Tests Form 312U at least 35 days before proposed use. Adjust batch proportions to compensate for surface moisture contained in the aggregates at the t ime of batching. Changes in the saturated surface dry mix proportions will not be permitted unless revised mix designs have been submitted to the Engineer and approved. Laboratory trial batches shall be created to confirm the proposed mix design meets the requirements of the plastic and hardened concrete . Accompany Materials and Tests Form 312U with a listing of laboratory test results of aggregate gradation, air content, slump and compressive strength from a certified laboratory. List the compressive str ength of at least three 6 inch x 12 inch or 4 inch x 8 inch cylinders at the age of 7 and 28 days.
Perform laboratory tests in accordance with the following test procedures: Property Test Method Aggregate Gradation AASHTO T Air Content AASHTO T 152 Slump AASHTO T 119 Compressive Strength AASHTO T 2 2 and R100 The Engineer will review the mix design for compliance with the Specifications and notify the Contractor as to its acceptability. Do not use a mix until written notice has been received. Acceptance of the mix design does not relieve the Contractor of his responsibility to furnish a product that meets the contract.
When a flowable concrete consistency is required, the use of an SCC or Intermediate Flow concrete is permitted with an approved concrete mix design. SCC is a specialized concrete mix that utilizes various admixtures to obtain a fluid consistency without negatively impacting the strength or homogeneity of the mix. SCC is designed to flow under its own weight and completely fill the formwork completely, even in the presence of dense reinforcement and without the need for consolidation. SCC is characterized by a plastic concrete mixture with a flow that achieves a spr ead of 22- 30 inches, when tested in accordance with ASTM C1611. Intermediate Flow Concrete is a concrete mix that exceeds the slump of standard concrete but does not have the same high flow characteristics of an SCC concrete mix.. Intermediate Flow Con crete is characterized by a plastic concrete mixture with a flow that achieves a spread of 16 -22 inches, when tested in accordance with ASTM C1611. When submitting a proposed SCC or Intermediate Flow concrete mix design on a Materials and Tests Form 312U , include the test results obtained using the following test procedures: Property Test Method Aggregate Gradation AASHTO T Air Content AASHTO T 152 Slump Flow ASTM C1611 Visual Stability Index (VSI) ASTM C1611 Passing Ability ASTMC1621 (Filling Procedure B) Segregation ASTM C1610 Compressive Strength AASHTO T 2 2 and R100 Supply concrete that develops a minimum compressive strength as shown in Table 1077- 1 unless other strengths are designated on the approved drawings. When required, air entrain concrete to provide an air content of 5 ± 2%. SCC and Intermediate Flow mixes shall have a difference in slump flow and passing ability not to exceed 2 inches, a Visual Stability Index no greater than 1, and a static segregation limit of 15%.
TABLE 1077 -1 PRECAST CONCRETE STRENGTH REQUIREMENTS AT AN AGE OF 28 DAYS Precast Units Requirement Specification Reference BARRIER: Portable 4,500 psi Section 854, 1090 and 1170 Permanent 4,500 psi Section 854, 857 and 1090 CULVERTS: Circular Pipe 4,000 psi Section 310, 1032, 1034, 1520 and AASHTO M 170 Single Cell Box Sections 5,000 psi Contract and AASHTO M 259 Pipe Tees 4,000 psi Section 310, 1032 and AASHTO M 170 Pipe Elbows 4,000 psi Section 310, 1032 and AASHTO M 170 Cross & Parallel Special End Sections 3,500 psi Section 310 and 1032 DRAINAGE STRUCTURES: Boxes (Solid & Waffle) 4,000 psi Section 840 and ASTM C913 CIRCULAR MANHOLES: Base 4,000 psi Section 1525 and AASHTO M 199 Riser Section 4,000 psi Section 1525 and AASHTO M 199 Top Section 4,000 psi Section 1525 and AASHTO M 199 Grade Ring 4,000 psi Section 858 and AASHTO M 199 WALLS AND PANELS: Wing, Head & End Walls 4,000 psi AASHTO T Precast Retaining Wall (PRW) Units 4,000 psi Section 455 Precast Coping 3,000 psi Contract Retaining Wall Panels 4,000 psi Contract Sound Barrier Wall Panels 4,500 psi Contract INCIDENTAL PRECAST ITEMS: Concrete Pads For Outlet Pipe, Controller Base Cabinets 2,500 psi Section 815, 816 and 825 Right -of-Way Markers 2,500 psi Section 806 and 1054 Concrete Anchor For Cable Guardrail 3,000 psi Section 1046 Picnic Tables 2,500 psi Contract Waste Containers 2,500 psi Contract Submit a proposed concrete mix design for the precast units to the Engineer . Determine quantities of fine and coarse aggregates necessary to provide concrete in accordance with this section by the method described in ACI 211 using the absolute volume method. The Engineer will review the mix design only to ascertain general compliance with the Standard Specifications . Do not use a mix until notified that the mix is acceptable.
Acceptance of the mix design does not relieve the Contractor of his r esponsibility to furnish an end product meeting the Standard Specifications .
Make all representative concrete test cylinders and all testing required herein in the presence of the plant inspector for items with strength requirements greater than 2,500 psi in Table 1077- 1, unless otherwise approved by the Engineer. For incidental precast items listed in Table 1077- 1, furnish a Type 3 material certification in accordance with Article 7 106-3 certifying that the item meets this Specification. Before t he first load is placed, determine the air content by AASHTO T 152, T196 or T121. If the air content does not meet the Standard Specifications , a second test on the same load is conducted using AASHTO T 152, T196 or T121. Acceptance or rejection of the load is based on the results of this test. Perform temperature, air , and slump or spread tests whenever cylinders are cast. Determine slump in accordance with AASHTO T 119 and ensure that slump meets the specifications as stated on Materials and Tests For m 312U approved mix design. For the purpose of testing for the required 28 day compressive strength, furnish, at no cost to the Department, at least four concrete cylinders for each class of concrete, each structure and each day that precast units are prod uced for the Department. If the contractor anticipates an early break request, furnish the Department with two concrete cylinders for each early break request. These cylinders are in addition to the four concrete cylinders required for each day of production. Make and cure cylinders in accordance with AASHTO R 100 unless, by permission of the Engineer, the units are cured by one of the methods in Article 1077- 9 for the full time required to meet the specified compressive strength requirements. In such case, cure the cylinders with the members and in the same manner as the members. Test cylinders in accordance with AASHTO T 22. If the average of two cylinders tested to determine compressive strength at the age of 28 days fails to indicate a compressive strength as shown in Table 1077- 1, or such compressive strength as is required by the approved drawings, such failure is cause for the rejection of the members represented.
Maintain the concrete temperature at the time of placing in the forms not less than 50°F nor more than 95°F unless otherwise directed by the Engineer. Place concrete in cold weather in accordance with Article 420 -7.
Use water reducing admixtures in accordance with Subarticle 1000 -3(G). Use high range water reducers (super plasticizers) , if approved by the Engineer. -6 FORMS Use forms of sturdy construction and in good working order which are capable of consistently providing straight lines and uniform di mensions in the finished product. Use metal forms except where other materials are approved by the Engineer. Provide an identifying number on each form, and mark each precast unit with the same identifying number as the form used to cast unit. Forms not meeting these requirements are subject to rejection by the Engineer. Provide joints in forms that are smooth and tight enough to prevent leakage of mortar. Provide inside surfaces of forms that are accessible for cleaning. After each use, clean the for ms thoroughly and inspect for damage . Repair or replace damaged forms that will not allow for proper casting or cause defects in the finished product. Before casting, free the inside surfaces of the forms from rust, grease or other foreign matter. Do not allow coatings used for release of members to build up and in no case allow liquid or powder from coating materials to come in contact with the reinforcement steel.
-7 REINFORCEMENT
Furnish steel reinforcement and place as shown in the plans and in accordance with Section 1070.
Substitute as an option, macro -synthetic fibers instead of 4 inches x 4 inches W1.4 x W1.4 welded wire reinforcement for selected precast concrete products in accordance with the following requirements.
Refer to Division 10. Item Section Portland Cement Concrete 1077 -5 Substitute macro -synthetic fibers only for steel reinforcement with an area of steel of 0.12 sq.in./ft or less in the following items:
No. 840.45.
Drawings No. 840.52. All other requirements, including reinforcement for these precast concrete items will remain the same.
Submit to the Department for approval by the precast producer and fiber manufacturer, independently performed test results certifying the macro- synthetic fibers and the precast concrete products meet the requirements listed herein.
Manufacture from virgin polyolefins (polypropylene and polyethylene) and comply with ASTM D7508. When using f ibers manufactured from materials other than polyolefins , submit test results complying with ASTM D7508 certifying resistance to long- term deterioration when in contact with the moisture and alkalies p resent in cement paste and/or the substances present in air -entraining and chemical admixtures. Fiber length shall be no less than 1.5 inches . Use macro -synthetic fibers with an aspect ratio (length divided by the equivalent diameter of the fiber) between 45 and 150, a minimum tensile strength of 40 ksi when tested in accordance with ASTM D3822 and a minimum modulus of elasticity of 400 ksi when tested in accordance with ASTM D3822.
Approved structural fibers may be used as a repl acement of steel reinforcement in allowable structures of Roadway Standard Drawings Nos. 840.45 and 840.52. The dosage rate, in pounds of fibers per cubic yard, shall be as recommended by the fiber manufacturer to provide a minimum average residual strength of concrete, tested in accordance with ASTM C1399, of no less than that of the concrete with the steel reinforcement that is being replaced and no less than 5 lb/cy. Submit the recommendations of the manufacturer that correlate the toughness of steel -reinforced concrete with that of the recommended dosage rate for the fiber -reinforced concrete.
Use fiber reinforced concrete with a 5% ± 2 % air content and a compressive strength of at least 4,000 psi in 28 days. Assure the fibers are well dispersed and pr event fiber balling during production. After introduction of all other ingredients, add the plastic concrete and mix the plastic concrete for at least 4 minutes or for 50 revolutions at standard mixing speed. -8 PLACING CONCRETE Use the procedures and equipment for handling, placing and consolidating the concrete such that a uniformly dense and high grade concrete is obtained in all parts of the unit under all working and w eather conditions. Do not mix, handle, deliver, place or finish concrete using devices made of aluminum or containing aluminum. Placing concrete for precast members in cold weather shall be in accordance with Article 1078 - 10. Internal, external or a combi nation of internal and external vibration is required as necessary to produce uniformly dense concrete without honeycomb. -9 CURING CONCRETE
Precast units are subjected to one of the methods of curing described below or to other methods or combinations of methods approved by the Engineer. Cure the precast units for a sufficient length of time so the concrete develops the specified compressive strength at 28 days or less. Do not strip forms until at least 24 hours after the concrete attains initial set. For this purpose, initial set is defined as at least 500 psi resistance to a standard penetrometer. The option to strip forms earlier is available provided concrete cylinders indicate a strength of at least 75% of the 28 day compressive strength is attained before release for each day’s production. Do not deface or injure the units.
Cure at elevated temperatures in accordance wit h Subarticle 1078 -11(B). The temperature within the curing enclosure shall not exceed 160°F. Place recording thermometers within each enclosure. Calibrate recording thermometers at intervals not to exceed 6 months. Submit complete temperature records to the Engineer for all cures before final approval of the members.
Water curing of precast units is allowed as described in Subarticle 420- 15(B), by covering with water saturated material, or by a system of perforated pipes, mechanical sprinklers, porous hoses or by any other method that keeps the units moist during the specified curing period. Do not use methods that deface or injure the precast units.
Application of a curing compound is allowed provided it is left intact until the specified compressive strength is met. Keep all surfaces moist before the application of the compound and damp when the compound is applied. Seal the surface with a single uniform coating at the rate of coverage recommended by the curing compound ma nufacturer, or as directed by the Engineer, but not less than 1 gal per 150 sf of area. -10 LIFT HOLES, HANDLING Do not cast or drill more than 4 holes in each unit for the purpose of handling or placing unless other wise approved by the Engineer. Locate all lift holes and handling devices in accordance with plan and design requirements. Units damaged while being handled or transported are rejected or require repair in a manner approved by the Engineer.
-11 FINAL FINISH Unless otherwise required by the contract, finish all concrete in accordance with Subarticle 420- 17(B) except as noted within Article 1077 -16. Do not repair units with honeycomb, cracks, or spalls until inspected by the Engineer. Use repair methods that are approved by the Engineer before their use. Any appreciable impairment of structural adequacy is ca use for rejection. -12 EXPOSED AGGREGATE FINISH FOR PRECAST CONCRETE PANELS When required, provide an exposed aggregate finish for front faces of panels with a depth of exposure ranging from 0 to 1/4 inch . Before beginning production, furnish three 12 inch x 12 inch sample panels to establish acceptable variations in color, texture and uniformity of the finish. After the sample panels are accepted by the Engineer and within 30 days of beginning production, produce a reinforced test panel of the largest size that wil l be used for the project with the accepted exposed aggregate finish. Acceptance of the appearance of panels during production will be based on the test panel and accepted sample panels. Use aggregate and cement from the same source as was used for the test panel and accepted sample panels to produce panels with an exposed aggregate finish. Provide access to visually inspect the entire finish of each completed panel and compare it to the test panel appearance before stacking panels. Replace the test panel with a new test panel every three months during production or when fly ash or cement source changes. -13 STEPS FOR PRECAST DRAINAGE STRUCTURES Supply steps meeting AASHTO M 199 for design, materials and dimensions. Incorporate steps in all drainage structures 3.5 f eet or greater in height. Do not detail the lowest step more than 16 inches from the bottom. -14 MARKING Clearly mark the following information on each precast member:
Clearly apply a Department approved self -adhesive RFID tag/label tagged in accordance with been inspected the Department will update the RFID tag/label record as found in the Field Inspection Report (FIR) o r NCDOT alternate ID . RFID tag/labels are allowed but not required for incidental precast items . -15 DIMENSIONS Ensure that all dimensions allow assembly of the units in place without objectionable deviation from the lines shown in the plans. If requested by the Engineer, assemble the precast members to ensure a quality fit before shipment of the precast members. -16 INCIDENTAL PRECAST ITEMS Furnish a Type 3 materials certification in accordance with Article 106 -3 for incidental precast items in Table 1077 -1. -17 SOUND AND NOISE WALL PANELS AND NOISE WALL POSTS Wall panels will be required to be placed in a rack system for inspection. Double faced wall panels will require access to both faces for proper inspection. After sound wall panels have been inspected and approved they shall be stored in a manner that will not cause damage prior to delivery to the project.