420CONCRETE STRUCTURES

4-31 (3) Inspection

Before the form or falsework system is loaded, inspect the erected falsework and forms and submit a written statement certifying that the erected falsework system complies with the accepted detailed drawings. Submit a separate certification for each span, unit or bridge component. Any condition that does not comply with the accepted drawings, or any other condition deemed unsatisfactory by the Engineer, is cause f or rejection until corrections are made.

420-4 Placing Concrete

Do not place concrete until the depth of the excavation, character of the foundation material, adequacy of the f orms and falsework, placement of reinforcement and other embedded items are inspected and approved. Do not place concrete without the Department’s i nspector present. Place concrete in daylight or obtain approval for an adequate lighting system for constru ction and inspection of the work. In preparation for the placing of concrete, remove all sawdust, chips and other construction debris and extraneous matter from the interior of forms. Remove hardened concrete and foreign matter from tools, screeds and con veying equipment. Ensure that the concrete temperature at the time of placement in the forms is at least 50°F and no more than 95 °F, except where other temperatures are required by Articles 420-7 and 420- 14. Do not use concrete that does not reach its final position in the forms within the time stipulated in Subarticle 1000- 3(E). Thoroughly clean and wet surfaces, other than foundation surfaces, immediately before placing concrete to help bonding to those surfaces. Regulate the placement of concrete so the pressures caused by the wet concrete do not exceed those used in the design of the forms. Thoroughly work the external surface of all concrete during the placing with approved tools. During the placing of concrete, take care to use methods of compaction that result in a surface of even texture free from voids, water or air pockets, and that force the coarse aggregate away from the forms to leave a mortar surface. Place concrete to avoid segregation of the materials and the displacement of the reinforcemen t. Equip chutes on steep slopes with baffle boards or provide chutes in short lengths that reverse the direction of movement. Use all chutes, troughs and pipes made from suitable materials other than aluminum and keep them clean and free from coating of hardened concrete by thoroughly flushing with water after each run. Discharge the water used for flushing clear of the structure. Confine concrete dropped more than 5 feet by closed chutes or pipes, except in walls of box culverts or retaining walls unless otherwise allowed by the Engineer . Take care to fill each part of the form by depositing the concrete as near to its final position as possible. Work the coarse aggregate back from the forms and around the reinforcement without displacing the bars. After initial set of the concrete, do not jar the forms and do not place strain on the projecting reinforcement or other items embedded in the concrete.

4-32 Compact all concrete required to be vibrated with approved high frequency internal vibrators

or other a pproved type of vibrators immediately after depositing concrete in the forms. In all cases, have available at least 2 vibrators in good operating condition and 2 sources of power at the site of any structure in which more than 25 cubic yard of concrete is required. Do not attach or hold the vibrators against the forms or the reinforcing steel. When vibrating concrete containing epoxy coated reinforcing steel, use a vibrator with a protective rubber head as approved by the Engineer. Vibrate with care and avoid displacement of reinforcement, ducts or other embedded elements. Vibrate in the appropriate location, manner and duration to secure maximum consolidation of the concrete without causing segregation of the mortar and coarse aggregate and without cau sing water to flush to the surface. When placing concrete to a depth in excess of 12 inches and containing one or more horizontal layers of reinforcing steel, place the concrete in horizontal layers not more than 12 inches thick. Place and compact each l ayer before the preceding layer takes initial set such that there is no surface of separation between layers. Do not taper layers of concrete in wedge -shaped slopes but instead place them with reasonably square ends and level tops. If placing additional c oncrete against hardened concrete, take care to remove all laitance and to roughen the surfaces of the concrete to ensure that fresh concrete is deposited upon sound concrete surfaces and an acceptable bond is obtained. Thoroughly wet the existing concret e for at least 2 hours before placing additional concrete. Deposit and compact to form a compact, dense, impervious concrete of uniform texture which shows smooth faces on exposed surfaces. Repair, remove and replace in whole or in part as directed by the Engineer and at no additional cost to the Department, any section of concrete found to be porous, cracked, plastered or otherwise defective. Protect beams and girders during concreting operations. Remove any concrete that gets on beams or girders immedia tely by an approved method to restore the surface to the specified condition. Any concrete placed in contact with aluminum or aluminized coatings shall have a barrier coat applied to the faying surfaces and edges of those steel components. Surface prepara tion and barrier coat paint systems are found in the Thermal Spray Coatings (Metallization) Program .

420-5 Pumping Concrete

Placement of concrete by pumping is permitted only when approved. Use and locate suitable pumping equipment that is adequate in capacity for the work and so no vibrations result which might damage freshly placed concrete. Do not use pumping equipment, including the conduit system, which contains any aluminum or aluminum alloy that comes in contact with the concrete. Waste all grout used to lubricate the inner surfaces of the conduit system. Pump so a continuous stream of concrete without air pockets is delivered. For test purposes, take concrete from th e discharge end of the pump.

420-6 Slump Tests

The slump of the concrete is determined in accordance with AASHTO T 119. When a slump test is made and the results of the test exceed the specified maximum allowed in Table 1000- 1, a check test is made immediately from the same batch or truck load of concrete. If a passing result cannot be produced on the check test the load will be rejected.

420-7 Placing Concrete In Cold Weather

4-33 higher than 150° F. Place the concrete when the temperature of the heated concrete is at

least 55°F and not more than 80° F. Use aggregates that are free of ice, frost and frozen particles. Do not place concrete on frozen foundation material. Protect all concrete with heated enclosures or by insulation whenever any of the following conditions occur:

4-34 conducted in accordance with ASTM C 1363 by an accredited commercial testing

laboratory for review, comments and acceptance by the Engineer . Obtain such acceptance before use of the material. Fa ce or cover insulating blankets, top and bottom, with polyethylene or similar waterproofing material meeting Article 1026- 3 except for the length and color requirements. Place blankets on the concrete to form a waterproof surface for the protected concret e. Do not use blankets with rips and tears in the waterproofing material unless acceptably repaired. When the anticipated low temperature expected during the protection period is less than 10° F, provide 2 inches of insulation. Overlap blanket insulation mats at the edges by at least 6 inches . Tightly butt rigid type insulation sheets together and seal. Take particular care to provide effective protection of curbs, corners and around protruding reinforcing steel. Should the air under the insulation fall below 50° F during the protection period, immediately cover the concrete with canvas and framework or other satisfactory housing and apply heat uniformly at a rate such that the air surrounding the concrete is at least 50°F for the remainder of the protect ion period. If insulating materials are removed from the concrete before the expiration of the curing period, cure the concrete for the remainder of the period in accordance with

420-8 Construction Joints

Provide construction joints only where located in the plan s or shown in the placing schedule, unless otherwise approved in writing. Place the concrete in each integral part of the structure continuously. Do not start work on any such part unless the concrete supply, forces and equipment are sufficient to complete the part 23 without interruption in the placing of the concrete. In case of emergency, make construction joints or remove the concrete as directed by the Engineer . Make construction joints without keys, except when required in the plan s. Rough float surfaces of fresh concrete at horizontal construction joints sufficiently to tho roughly consolidate the concrete at the surface. After placing concrete to the construction joint and before placing fresh concrete, thoroughly clean the entire surface of horizontal and vertical construction joints of surface laitance, curing compound and other materials foreign to the concrete. Thoroughly clean and wet concrete surfaces for at least 2 hours before placing additional concrete to help bonding.

420-9 Widening Ex Isting Structures

Where plans call for widening existing concrete structures or otherwise require bonding new concrete to old, remove portions of the existing structures as indicated in the plans and in accordance with Subarticle 40 2-2(C). When extending an existing culvert, remove the following portions of the existing culvert: the portions that interfere with the proposed extension, headwalls only as necessary to clear proposed subgrade by at least 18 inches and wingwalls to square surfaces the full thi ckness of the new sidewalls. Cut existing wingwall reinforcing steel off flush with the concrete surface. Thoroughly roughen, clean of f loose material and wet connecting surfaces of the old concrete at least 2 hours before placing new concrete.

420-10 Expansion Joints

4-35 Immediately after removing the forms, inspect the expansion joint carefully.

Neatly remove any concrete or mortar in the joint.

420-11 Drains In Walls and Culverts

Construct drain holes and weep holes in abutment walls, wing walls, retaining walls and the exterior walls of culverts as shown in the plan s unless otherwise directed by the Engineer and backfill in accordance with Article s 414-7 and 414- 8. Cover drain holes and weep holes at the back face of the wall with hardware cloth of commercial quality, approximately No. 4 galvanized steel wire reinforcement .

420-12 Anchor Bolts and Bearing Areas

4-36 420-13 Adhesively Anchored Anchor Bolts Or Dowel S

4-37 bolt/dowel yield load as listed in the plans and in accordance with Subarticle 1081-

1(C). Installation of the adhesive anchors sha ll be in accordance with the MPII and shall occur when the concrete is above 40° F (unless the MPII requires a higher temperature) and has reached its 28 day strength. The anchors shall be installed before the adhesive’s initial set ( gel time). Insert the anchor bolt/dowel the specified depth into the hole and slightly agitate it to ensure wetting and complete encapsulation. After insertion of the anchor bolt/dowel, strike off any excessive adhesive flush with the concrete face. Should the adhesive fail to fill the hole, add ing additional adhesive to the hole is not allowed . In such cases, remove the anchor and submit a repair procedure to the Engineer. Do not disturb the anchor bolts/dowels while adhesive is hardening.

4-38 Remove all anchors or dowels that fail the field test without damage to the surrounding

concrete. Redrill holes to remove adhesive bonding material residue and clean the hole in accordance with specifications. For reinstalling replacement anchors or dowels, follow the same procedures as new installations. Do not reuse failed anchors or dowels unless approved by the Engineer.

420-14 Placing and Finishing Bridge Decks

4-39 measurement by the Engineer of deflection as it occurs. Unless otherwise permitted, d o

not adjust the profile grade -line for any of the forming types used. Cast the concrete in accordance with the pour sequence shown in the plan s, unless otherwise approved by the Engineer . Place concrete in a continuous manner between header s. Use approved screeds, screed supports and screeding methods.

4-40 straightedge as a finishing tool. Give surfaces adjac ent to expansion joints special attention

to assure they meet the required smoothness. Provide on-site fogging equipment which is capable of applying water to the concrete in the form of a fine fog mist in sufficient quantity to curb the effects of rapid evaporation of mixing water from the concrete on the bridge deck resulting from wind, high temperature, low humidity or a combination of these factors. Do not apply the moisture from the nozzle under pressure directly upon the concrete and do not allow it to accumulate on the surface in a quantity sufficient to cause a flow or wash the surface. Maintain r esponsibility for determining when to apply the fog mist but apply it when directed by the Engineer . Keep readily available on site an adequate supply of suitable coverings that will protect the surface of the freshly placed bridge deck from rain. After t he water sheen disappears from the surface and before the concrete becomes non -plastic, finish the surface of the floor further by burlap dragging, fine bristle brooming, belting or other acceptable method which produces an acceptable uniform texture. Do n ot use membrane curing compound unless approved. Cure the concrete using the water method in accordance with Suba rticle 420 -15(B), with the following exceptions. Before reaching initial set, place a curing medium consisting of burlap under polyethylene sheets or another approved material on the deck and keep moist for at least 7 curing days. Wet the burlap or other approved curing medium before placing on the deck. Apply water to the curing medium through soaker hoses or another approved method. Apply water in amounts to keep the medium moist but do not allow the water to flow or pond on the deck. After curing the concrete, test the finished surface with an approved rolling straightedge designed, constructed and adjusted to accurately indicate or mark a ll floor areas which deviate from a plane surface by more than 1/8 inch in 10 feet. If required by the Engineer , further test any areas of concern using a 10 foot stationary straightedge furnished by the Contractor. Remove all high areas in the hardened surface in excess of 1/8 inch in 10 feet with an approved grinding or cutting machine. Where variations are such that the corrections will extend below the limits of the top layer of grout, seal the corrected surface with an approved sealing agent as required. Submit proposed corrective measures to the Engineer for approval for all low areas in excess of 1/8 inch in 10 feet . Produce corrected areas that have a rough, uniform texture and present neat patterns. In all cases, maintain at least 2 inches of concrete cover over reinforcement. Unless otherwise indicated in the plan s, groove bridge decks . Produce grooves perpendicular to the centerline of bridge. Do not start grooving until final straightedging and, when necessary, acceptable corrective measures are complete. Cut grooves into the hardened concrete using a mechanical saw device, which leaves rectangular grooves 1/8 inch wide and 3/16 inch deep. Produce grooves that have a center to center spacing of 3/4 inch. Do not groove the deck surface within 18 inches of the gutter lines and 2 inches of expansion joints or elastomeric conc rete in expansion joint blockouts. On skewed bridges, ungrooved triangular areas adjacent to the joint are permitted, provided the distance from the centerline joint to the nearest groove, as measured parallel to the centerline of roadway, does not exceed 18 inches . Between expansion joints on horizontally curved bridges, periodically adjust the grooving operation such that adjacent grooves are separated by no more than 3 inches along the outer radius of the bridge deck. Continuously remove all slurry or other residue resulting from the grooving operation from the bridge deck by vacuum pick- up or other approved methods. Prevent slurry from flowing into deck drains or onto the ground or body of water under the bridge. Dispose of all residue by an approved method.

4-41 directed by the Engineer . For at least 25% of the individual form panels, as selected by the

Engineer, hammer test over the entire area of the panel. If areas of doubtful soundness are disclosed by this procedure, remove the forms from such areas for visual inspection after the pour attains a minimum compressive st rength of 2, 400 psi. Remove the stay- in-place forms. At locations where sections of the forms are removed, do not replace the forms, but repair the adjacent metal forms and supports to present a neat appearance and assure their satisfactory retention. As soon as the forms are removed, allow the Engineer to examine for cavities, honeycombs and other defects. If irregularities are found, and in the opinion of the Engineer these irregularities do not justify rejection of the work, repair the concrete as dir ected by the Engineer . If the concrete where the forms are removed is unsatisfactory, remove additional forms, as necessary, to inspect and repair the slab. Modify the methods of construction as required to obtain satisfactory concrete in the slabs. Rem ove and repair all unsatisfactory concrete as directed by the Engineer . Provide all facilities as are reasonably required for the safe and convenient conduct of the Engineer’s inspection procedures.

420-15 Curing Concrete

4-42 (C) Membrane Curing Compound Method

Spray the entire surface of the concrete uniformly with a curing compound that is on the NCDOT APL. Use clear curing compound to which a fugitive dye is added for color contrast on bridge superstructures , substructures and retaining walls. Use either white pigmented or clear curing compound on culverts. Apply the membrane curing compound after the surface finishing is complete and immediately after the free surface moisture disappears. During the finishing period, protect the concrete by applying water with the fogging equipm ent specified in Subarticle 420- 15(B). Seal the surface with a single uniform coating of the specified type of curing compound applied at the rate of coverage recommended by the manufacturer or as directed, but at least one gallon per 150 square feet of surface area. At the time of use, th oroughly mix the compound with the pigment uniformly dispersed throughout the vehicle. If the application of the compound does not result in satisfactory coverage, stop the method and begin water curing, as set out above, until the cause of the defective work is corrected. At locations where the coating shows discontinuities, pinholes or other defects, or if rain falls on the newly coated surface before the film dries sufficiently to resist damage, apply an additional coat of the compound at the same rate specified herein immediately after the rain stops. Completely remove any curing compound adhering to a surface to which new concrete is to be bonded by sandblasting, steel wire brushes, bush hammers or other approved means. Protect the concrete surfaces to which the compound is applied from abrasion or other damage that results in perforation of the membrane film for 7 curing days after placing the concrete. If the film of membrane compound is damaged or removed before the expiration of 7 curing days, imme diately cure the exposed concrete by the water method until the expiration of the 7 curing days or until applying additional curing compound. If the application of curing compound is delayed, immediately start applying wate r as provided in Subarticle 420 -15(B) and continue until resuming or starting application of the compound.

4-43 (E) Forms -in-Place Method

As an option, cure surfaces of concrete by retaining the forms in place for at least 7 curing days after placing the concrete. If electing to leave forms in place for a part of the curing period and using one of the other methods of curing included in this article for the remainder of the curing period, keep the concrete surfaces wet during transition between curing methods.

420-16 Removal of Forms and Falsework

Do not remove forms and falsework for the portions of structures listed in Table 420- 1 until the concrete attains the compressive strength shown, as evidenced by approved, nondestructive test methods or by conducting compressive strength tests in accordance with AASHTO T 22 and T 23. Furnish approved equipment used for nondestructive tests. TABLE 420-1 MINIMUM CONCRETE STRENGTH FOR REMOVAL OF FORMS AND FALSEWORK Portion of Structure Minimum Compressive Strength, psi Bridge deck slabs and overhangs for beam and girder bridges 3,000 Arch culverts, top slabs of box culverts, walls of box culverts when cast monolithically with the top slab or when the wall is 10 ft or more in height, caps and struts of subs tructures, diaphragms and other members subject to dead load bending 2,400 Remove forms for ornamental work, railing, parapets, walls less than 10 feet in height, curb faces on bridge superstructures and vertical surfaces that do not carry loads, any time after 3 hours if the concrete is set sufficiently to permit form removal without damage to the member. Do not remove forms used for insulation before the expiration of the minimum protective period required in Article 420 -7. Do not remove formwork for bent diaphragms until after casting deck concrete and allowing the concrete to attain a strength of 2,400 psi. As an option, to remove support from bent diaphragms before casting deck concrete, submit for approval a method to prevent the possibility of bent diaphragms slipping downward. When removing forms before the end of the required curing period, use other curing methods to complete the required curing. When removing forms from underneath slabs before the end of the curing period, complete the curing in accordance with Subarticle 420 -15(C).

420-17 Surface Finish

4-44 During the placing of concrete, take care to use methods of compaction that result in

a surface of even texture free from voids, water or air pockets, and that the coarse aggregate is forced away from the forms to leave a mortar surface. Immediately after removi ng the forms, clean and fill with grout all pockets, depressions, honeycombs and other defects as directed. Remove all form ties or metal spacers to a depth of at least 1 inch below the surface of the concrete then clean and fill the resulting holes or depressions with grout. As an option, break off flush with the concrete surface those metal devices with exposed cross -sectional area not exceeding 0.05 square inches on surfaces permanently in contact with earth fill. Unless otherwise required, remove fin s and other projections flush with the concrete surface. Remove stains and discoloration. Use grout for patching which contains cement and fine aggregate from the same sources and in the same proportions as used in the concrete. Cure the grout in accorda nce with

4-45 good abrasive to bring the surface to a smooth texture and remove all form marks. Finish

the paste formed by rubbing as des cribed above by carefully stroking with a clean brush, or spread it uniformly over the surface and allow it to take a reset, then finish it by floating with a canvas, carpet -faced or cork float; or rub down with dry burlap.

420-18 Epoxy Coating

420-19 Protection of Substructure Concrete From Rust Stains

To prevent unpainted structural steel from staining substructure concrete, protect all final exposed areas of the concrete from rust stains until casting the bridge deck and sealing the expansion joints. Use an approved method for protecting the concrete. Instead of the above, remove the stains by approved methods and cleaning agents.

420-20 Placing Load On Structure Members

Do not place beams or girders on concrete substructures unti l the concrete in the substructure develops a minimum compressive strength of 2,400 psi. In addition to Article 410 -8, do not place backfill or fill for retaining walls, abutments, piers, wing walls or other structures that will retain material to an eleva tion higher on one side than the other until the concrete develops the minimum specified strength for the class of concrete required for the structure as listed in Table 1000 -1. In addition to Article 414 -7, do not place backfill or embankment behind the w alls of culverts to an elevation higher than one foot above the top of footing or bottom slab until after placing

4-46 the top slab and until the concrete develops the minimum required strength for the class of

concrete specified as listed in Table 1000 -1. Do n ot pour walls of culverts until floor slabs develop a minimum compressive strength of 2,400 psi. Unless independently supported, do not pour roof slabs of culverts until the concrete in the culvert walls develops a minimum compressive strength of 2,400 ps i. Do not operate heavy equipment over any culvert type until properly backfilling with a minimum cover of 3 feet. Adhere to the following time and strength requirements for erection of forms and construction of superimposed bridge substructure elements:

420-21 Measurement and Payment

Class ____ Concrete will be measured and paid as the number of cubic yards of each class that is incorporated into the completed and accepted structure except as indicated below. The number of cubic yards of concrete is computed from the dimensions shown in the plans or fro m revised dimensions authorized by the Engineer. When the foundation material is rock, the number of cubic yards of footing concrete is computed by the average end area method using the lower limits established for foundation excavation. The volume of concrete displaced by piles other than steel piles is not include d in the quantity to be paid .

4-47 Grooving Bridge Floors will be measured and be paid as the actual number of square feet shown

in the plan s. Where the plans are revised, the quantity to be paid is the quantity shown on the revised plans. Reinforced Concrete Deck Slab and Reinforced Concrete Deck Slab (Sand Lightweight Concrete ) will be measured and paid as the number of square feet shown in the plan s. No separate payment will be made for furnishi ng and incorporating calcium nitrite corrosion inhibi tor when required by the plans. The plan quantity is determined from the horizontal surface area using the nominal dimensions and configuration shown in the Layout Sketch for computing surface area as shown in the plans. Measure t he transverse dimension out to the slab including raised median and sidewalk sections. Consider concrete diaphragms a portion of the slab. When required by the plans, consider curtain walls, raised medians, sidewalks, pavement brackets, end posts, sign mounts, luminaire brackets and any other concrete appurtenances or expansion joint material a portion of the slab . Concrete barrier rail (including curved end blocks for the concrete barrier rail, when used) is not considered a portion of the slab . For structural steel spans, the quantities of concrete and reinforcing steel shown in the plan s are based on a metal stay -in-place forming metho d. These quantities include amounts for 1 inch additional concrete due to the corrugation of the metal forms, concrete diaphragms and, when required by the plans, curtain walls, pavement brackets, end posts, raised medians, sidewalks an d other required attachments based on the profile grade and plan camber of the girders. For prestressed concrete girder spans, the quantities of concrete and reinforcing steel shown in the plan s are based on the forming method detailed in the plan s. These quantities include concrete diaphragms, and, when required by the plans, curtain walls, pavement brackets, end posts, raised medians, sidewalks and other required attachments based on the profile grade and plan camber of girders. The quantities include e ither CIP slab concrete when the plans are detailed for the prestressed concrete panel forming method or amounts for 1 inch additional concrete due to the corrugation of the metal forms when the plans are detailed for the fabricated metal stay -in-place for m forming method and based on the profile grade and plan camber of the girders. No measurement will be made for concrete or reinforcing steel due to a variation in camber of the girders from the plan camber or for additional quantities required by optional methods of forming. No separate measurement or payment will be made for furnishing, installing and testing anchor bolts or dowels. Payment at the contract unit prices for the various pay items will be full compensation for all materials, equipment, tools , labor and incidentals necessary to complete the work. These prices and payments will be full compensation for all items required to construct concrete structures. Remove forms and r epair, remove or replace, as directed , concrete containing plastic shrin kage cracks or other defects at no cost to the Department. Payment will be made under: Pay Item Pay Unit Class ____ Concrete Cubic Yard Grooving Bridge Floors Square Foot Reinforced Concrete Deck Slab Square Foot Reinforced Concrete Deck Slab (Sand Lightweight Concrete) Square Foot