- 479 - SECTION 704 -- CONCRETE CONSTRUCTION
704.01 Description
1.This work shall consist of fa lsework and form construction and the handling, placing, curing, and finishing of concrete for bridges, box culverts, arch culverts, headwalls, concrete seals, retaining walls and steps, foundations, substructures, and miscella neous structures. All work shall be done in accordance with these S pecifications and the contract.
2.Also included in this Section is all work necessary to adapt existing structures for extension or reconstruction.
704.02 Material Requirements
1.The class of concrete shall be sh own in the contract or specified in the special provisions.
2.When the contract or special pr ovisions allow the use of more than one class of concrete, the Contractor sh all advise the Engineer of the class of concrete to be used before the date of beginning of concrete construction on any project. No change shall be made in the class of concrete during the progress of the work without the written permission of the Engineer.
3.Materials shall conform to the requirements in Table 704.01. Table 704.01 Material Requirements Applicable Materials Section Anchor Bolts ..................................................... .1057, 1058 Curing Ma terials ................................................ .1010, 1011, 1012 Deformed Metal Center Joints and Metal Ke yway ................................................... . Dowel Ba rs ....................................................... .1022 Galvanized Ha rdware ....................................... .1059 Joint Sealing Filler ............................................. .1014 Paint and Pain t Materials .................................. .1077 Portland Cement Concrete ............................... .1002 Preformed Jo int Filler ........................................ .1015 Reinforcing Steel ............................................... .1020, 1023, 1024 Epoxy Coated Rein forcing Steel ....................... .1021 Structural Steel ................................................. . 708
704.03 Construction Methods
1.The Contractor shall construct c oncrete structures as described in the contract. All concrete rails on bridges and approach slabs shall be cast- in-place. Slip-forming will not be permitted for concrete rails on bridges and approach slabs.
2.Foundation Preparation:
a.Foundation excavations shall be as dry as practicable before concrete is placed.
b.In the event that the Contractor is required to excavate for spread footings to depths greater t han those shown in the contract, the Engineer will redesign the structure' s outline and reinforcement and provide the Contractor the appropriate revised plans.
704.03 Concrete Construction
- 480 - 3. Rock Anchors for Spread Footings:
a.The Contractor shall anchor spread footings resting on rock with reinforcing bars of the size, lengt h, and number shown in the contract.
b.In rock, the reinforcing hole diameters shall be at least 2 times the bar diameters and shall be drilled to the depth indicated in the contract.
c.The bars shall be centered in the holes and grouted in place.
d.The grout shall be compos ed of 1 part cement and 2 parts sand and shall be placed by a method which will insure that the hole is completely fill ed with grout.
e.Reinforcing bar holes need not be pumped out when grouting the bars if the method that is used for placing the grout does not cause grout mix segregation.
4.Concrete Seal Course: a. When shown in the cont ract or when conditions are encountered which render it impossibl e or impracticable to dewater the foundation bed in a satisfactory ma nner before and during the concrete placement, the Contractor shall be required to construct a concrete foundation seal course below the elevatio n of the footing of such dimensions as may be necessary.
b.Concrete for such seal course shall conform to the requirements for concrete placed in still water as described in Paragraph 11. of this Subsection.
c.When the seal course has been in place for at least 72 hours after completing the final placement, t he cofferdam shall be cleared of water. The seal shall be capable of excluding water from below so that the balance of the structure may be completed.
d.Pumping from the interior of any foundation enclosure shall be done in such a manner as to preclude the possibility of the movement of water through the fresh concrete.
e.No pumping will be allowed while placing the concrete, or for 24 hours thereafter, unless it is done fr om a suitable sump separated from the concrete work by a watertight wall or other effective means.
5.Falsework: a. The Contractor is responsib le for the falsework and its design. The falsework shall be designed and sealed by a Professional Engineer registered in Nebraska.
b.The Contractor shall submit falsework plans when they are required by the contract, special provis ions or for the following construction requirements:
1.Support of plastic concrete for concrete slab bridges with spans greater than 50 feet (15 m) in length.
2.Support of girders or ot her large structural elements when falsework is used.
3.Concrete deck cantilevers more than 6 feet (1.8 m) beyond the exterior girder. Concrete Construction 704.03 - 481 - c. Falsework design submittals shall meet the following criteria:
1.Detailed falsework plans shall be submitted to the Department, in triplicate, and for information only. The supporting calculations or evidence of adequacy are also required by the Department.
2.Falsework plans and calculations shall bear the seal of a Professional Engineer registered in Nebraska.
3.The design of the falsework shall meet the requirements in AASHTO's Standard Specifications for Highway Bridges and the Guide Design Specification for Bridge Temporary Works .
4.The falsework plans must be submitted to the Department prior to erection of any falsework elements.
5.The Department's request for falsework plans and calculations will in no way constitute review and approval, and the Contractor shall be solely responsible for the falsework and its design.
d.All falsework shall be design ed and constructed to support the loads without appreciable settlement or deformation. The Contractor shall construct all falsework according to the falsework plans submitted.
e.(1) Falsework may be supported by pilings which shall be spaced, driven, and removed in a manner satisfactory to the Engineer.
2.Falsework may also be supported by beams hung from the bridge's permanent substructure with the written approval of the Engineer. The Contractor shall repair any damage at no cost to the Department.
3.Falsework for highway grade separation structure may be supported by mudsills if they are large enough to provide necessary support of the load.
4.All falsework shall be removed after the structure is complete.
f.Falsework construction shall not begin until the contractor has complied with the conditions in Section 704.03 5.c.
g.Falsework shall be set up to produce a finished structure at the elevations and grades indicated in the contract. The Contractor shall consider and compensate for deflections that the method of construction creates.
h.Materials for falsework may be either new or used. All materials are subject to inspection by the Engineer to determine if they are suitable for their intended use. All materials which the Engineer determines to be damaged, defective, or otherwise unsuitable for use will be rejected.
i.Falsework and falsework su pports shall be protected against impact and the effects of vibration by placement of barriers or limiting the access of construction equipment.
j.All falsework piles in the stream channel shall be pulled when no longer needed.
704.03 Concrete Construction
- 482 - 6. Forms:
a.Formwork shall be constructed in accordance with the current AASHTO Guide Design Specification for Bridge Temporary Works .
b.Forms for concrete shall conform to the dimensions, lines, and grades shown in the contract. They shall be substantial, unyielding, and constructed mortar tight. They shall be su fficiently rigid to prevent distortion due to pressures of concrete, vibrati on, and other loads incidental to the construction operations.
c.Form Materials: (1) Aluminum or other materials that react adversely with the concrete shall not be used in the forms.
2.Form liners shall be m ade of plywood, water-resistant composition board, or other approved material. Only one type of liner shall be used throughout the structure. Liners shall be a uniform size and as large as practical. Joints shall be tight and smoothly cut.
3.Forms for 42 inch bridge rails shall be made of steel. Wood forms that are commercially manufactured to the specific shape of the 42 inch rail may be permitted. Forms shall be capable of producing a uniform surface, texture and appearance equal to that obtained by using steel panels in good condition.
d.Form Design: (1) Concrete for exposed surfaces shall be cast against form panels or surfaces capable of produc ing a uniform surface, texture, and appearance at least equal to that obtained by using plywood form panels of good condition.
2.Forms not capable of producing such a surface shall be lined.
3.Adjacent panels shall be oriented and aligned so that the joints and grain give a continuous, uniform appearance.
4.Forms shall be fillet ed or chamfered approximately 3/4 inch (19 mm) at all exposed corners.
5.Forms shall be set and maintained true to the line designated without the use of te mporary internal bracing.
6.Form surfaces shall be treated with a nonstaining form oil or other approved material. No material which will adhere to or discolor the concrete shall be used.
7.Metal ties or anchorages within the forms shall be designed to allow their removal to a de pth of at least 1/2 inch (13 mm) from the face without damaging the concrete.
8.Tie and anchorage cavities shall be filled with cement mortar and the surface left sound, sm ooth, even, and uniform in color.
9.Protruding ends of plastic ties shall be removed flush with the concrete surface.
10.When a monolithic layer cannot be completed in one operation, it shall be terminated in a vertical bulkhead. Concrete Construction 704.03 - 483 - e. Successive Pours:
1.Twelve hours after placing concrete, the reinforcing steel and form work for the succeeding pours may be set on the curing concrete.
2.It is recognized that fo r the forming to proceed, it will be necessary to remove the wet burlap from the specific areas where the forming will take place. The exposed area shall be kept to an absolute minimum and shall be kept damp.
3.Reinforcing steel and form work for bridge curbs and bridge rails shall not be placed until after the 10-day wet curing.
f.Girder Bridge Deck Forms: (1) Forms for concrete floor slabs on steel or precast concrete girders or beams shall be hung from adequate metal hangers.
2.Forms shall be adjustable to vary the slab thickness. (3) Forms shall be of such substantial design that no measurable settlement of forms occurs when the concrete deck is placed.
4.Tack welding of form hangers or other miscellaneous hardware to the flanges of girders is prohibited.
g.Steel stay-in-place forms will be allowed for concrete floor slabs on steel or precast concrete “I” girders. Stay-in-place forms shall be used for interior areas only, where the forms are supported on both sides by girders. Stay-in-place forms must be adjustable to maintain proper slab thickness and shall be designed so no measurable settlement of forms occurs when the concrete deck is poured. Stay-in-place form support systems must be designed so as to maintain a minimum 1/2 inch (12 mm) clearance between the form support and the bridge deck reinforcing steel. Removable forms must be used outsi de of the exterior girders.
1.The form corrugations shall be filled with polystyrene strips to prevent excess slab dead load.
2.The Contractor shall subm it four copies of the stay-in- place form design plans and computations to the Engineer prior to construction. These plans and computations are for information only. The Contractor is responsible for the per formance of the stay-in-place forms.
3.Steel stay-in-place form material shall conform to the requirements of ASTM A 653/A 653M Coating Designation G615/Z500.
4.The stay-in-place forms will not be measured and paid for directly but shall be considered subsidiary to the item Class 47BD-_____ Concrete for Bridges.
7.Removal of Forms and Falsework:
a.Falsework and forms shall not be removed without the approval of the Engineer.
b.Forms:
1.Forms shall not be removed until the concrete has sufficient strength to prevent damage to the concrete.
704.03 Concrete Construction
- 484 - (2) Forms not supporting the dead weight of the concrete shall remain in place for a minimum of 24 hours, exclusive of time which the air temperature is below 40 ˚F unless external heating is used.
i.Forms for bridge barrier rail may be removed after 12 hours, exclusive of time whic h the air temperature is below 40 ˚F unless external heating is used. (ii) Forms for vertical surfaces requiring a rubbed finish may be removed after 12 hours.
3.Forms supporting the dead weight of the concrete shall remain in place in accordance with the requirements for falsework.
c.Falsework: (1) Falsework for bridges: (i) Falsework and supporting forms shall not be removed until the concrete has reached 70% of the required compressive strength. (ii) Falsework and supporting forms shall remain in place for a minimum of 5 days after the pour, with the following exceptions:
a.Supporting forms for open rails shall remain in place for a minimum of 3 days.
b.Supporting forms for overhangs less than 8 inches shall remain in place a minimum of 24 hours. (iii) In the absence of compressive strength test, falsework and supporting forms shall remain in place 10 days, exclusive of the time during which the temperature is below 40 ˚F unless external heating is used.
2.Falsework for box culverts: (i) Falsework and supporting forms shall not be removed until the top slab has reached 70% the design compressive strength. (ii) In the absence of compressive strength test, falsework for top slabs shall remain in place 7 days, exclusive of the time during which the temperature is below 40 ˚F unless external heating is used.
3.Supports shall be removed gradually so as to allow the concrete to support its own weight uniformly.
i.Falsework supports shall be released near the center of the span and progress toward the end supports. (ii) All falsework piles shall be removed in accordance with the requirements of Subsection 203.02, Paragraph 13.
8.Reinforcing steel shall be placed as described in Subsection 707.03.
9.Preparation of Bearing Areas and Setting Anchor Bolts: a. The Contractor shall pre pare bridge seats for bearing devices and shall finish the bridge seats to the elevations shown in the contract. The top shall form a true cont inuous plane surface.
b.Anchor bolts shall be set at the time of placing the concrete, or they may be placed and grouted in blocked out holes. Concrete Construction 704.03 - 485 - c. Anchor bolts shall be set pl umb and at the proper location and elevation with templets.
d.Blocked out wells for grouted anchor bolts may be either round or square and shall be 1 1/2 inches ( 38 mm) larger than the bolt diameter. An approved non-shrink grout shall be placed and vibrated or tamped to completely fill the well.
e.Drilling holes for anchor bolts is not allowed.
10.Placing Concrete: a. Preparation: (1) The Contractor shall gi ve the Engineer 1 NDOT work day advance notice before starting to place co ncrete in each unit of the structure.
2.The forms and the reinforcement for a structure shall be set before any concrete is placed.
3.Concrete shall not be placed in structures bearing on the soil until all pile driving within a radius of 25 feet (7.6 m) has been completed. If concrete pours must be made within this area before completion of pile driving, such concrete shall cure at least 3 days before further driving is allowed.
4.All dirt, sawdust, and other extraneous materials shall be removed from the forms before concrete is placed.
5.Concrete shall not be placed in the superstructure until the substructure forms have been stripped and the concrete inspected for defects. The load of the superstructure shall not be allowed to bear on the substructure until its concrete has attained a compressive strength of 2,000 psi (14 MPa).
b.Equipment: (1) When authorized by the Engineer, chutes and pipes may be used for conveying concrete to the forms.
2.Equipment shall be arrang ed so that segregation does not occur.
3.When steep chutes are necessary, the chutes shall be equipped with baffle boards or shall be in short sections that reverse the direction of the concrete's movement.
4.All chutes and pipe shall be metal, metal lined plastic, rubber, or other nonreactive material.
5.Chutes shall be kept clean and free from concrete coatings.
6.Aluminum or aluminum allo ys that react with the concrete shall not be used for chutes
c.Environmental Conditions:
1.Concrete shall not be placed when weather conditions may damage the concrete or prevent proper construction.
2.Mixing and concreting operations shall be discontinued when the descending ambient air temperature reaches 40°F (4°C) and shall
704.03 Concrete Construction
- 486 - not be resumed until an ascending ambient air temperature reaches 35°F (2°C).
3.Concrete shall not be placed on frozen material. When concrete is being placed and the air temperature may be expected to drop below 35°F (2°C), the conc rete shall be protected.
d.Placement: (1) The Contractor shall pl ace concrete in one continuous operation.
2.The maximum allowable interval for placing successive concrete batches into fo rms shall be 30 minutes.
3.The sequence of placing concrete shall be as shown in the contract.
4.Depositing and consolidating the concrete shall be done so that voids are not induced and the concrete is uniform and has smooth faces on all surfaces.
5.Material segregation and displacement of the reinforcement shall be avoided.
6.Concrete in girders shall be deposited uniformly for the full length of the girder and brought up in horizontal layers.
7.Concrete placement shall be regulated to control fluid pressures.
8.Special care shall be taken to work the coarse aggregate back from the face of the forms and to force the concrete under and around the reinforcement bars without displacing them.
9.After the concrete has taken its initial set, care shall be exercised to avoid jarring the forms or placing any strain on the ends of projecting bars.
10.After placing concrete in the forms, the concrete shall not be moved laterally more than 6 feet (1.8 m). Use of a vibrator to move concrete shall be prohibited.
11.The forms shall be filled uniformly.
12.Concrete free fall distance shall not exceed 5 feet (1.5 m). This includes free fall in a discharge pipe.
13.The concrete shall be discharged in a continuous stream free of air pockets so that a constant pressure head is maintained.
11.Placing Concrete Under Water: a. The Engineer shall approve all concrete placed under water. b. Concrete placed under water shall be the same class and mix as used in the remainder of the stru cture except cement content shall be increased 10%. c . T r e m i e :
1.The tremie shall consis t of a watertight tube having a diameter of not less than 10 inches (250 mm). It shall be constructed in sections having flexible, watertight couplings. Concrete Construction 704.03 - 487 - (2) The tremies shall not be constructed of aluminum or aluminum alloy that will react with the concrete.
3.The tremies shall be supported to allow free movement of the discharge-end over the entire top surface of the work. They shall allow rapid lowering when necessary to retard or stop the concrete flow.
d.Placing Concrete: (1) The discharge end shall be closed at the start of the work so as to prevent water fr om entering the tube and shall be entirely sealed at all times. The tremie tube shall be kept full at all times.
2.When a batch is dumped into the hopper, the concrete flow shall be induced by slightly raising the discharge-end and yet always keeping it in the concrete that is being deposited.
3.The flow shall be continuous until work is completed.
4.Concrete shall be placed continuously from start to finish. The surface of the concrete shall be k ept as nearly horizontal as practicable at all times.
5.Concrete shall be tremied in place forming a compact mass free of voids. It shall not be disturbed after being deposited.
6.Still water shall be maintained at the point of deposit, and the forms shall be watertight.
d.Once the concrete has set, standing water shall be removed, the concrete inspected, and all laitance or other unsatisfactory material shall be removed from the surfaces.
12.Pumping: a. Concrete that is pumped into a form shall be in a continuous stream and free of air pockets. The conc rete in the pipeline shall be ejected in such a manner that there will be no contamination or segregation of the concrete.
b.Pump discharge pipes shall be designed to maintain a positive pressure head on concrete, and the free fall distance shall not exceed 5 feet (1.5 m) at discharge.
c.Air tests, slump tests, and fa brication of concrete test cylinders shall be performed at the final discharge point.
13.Consolidation of Concrete:
a.The Contractor shall consolidate all concrete to a uniform density. Consolidation shall be accomplished by mechanical vibration during and immediately after being placed as described in this Subsection.
1.Concrete shall be placed in continuous horizontal layers not more than 18 inc hes (450 mm) thick.
2.Each layer shall be placed and consolidated before the preceding layer has taken an initial set.
b.Internal vibration shall be used. c. Vibrators:
1.Vibrators shall be approved by the Engineer.
704.03 Concrete Construction
- 488 - (2) The vibration frequenc y shall be greater than 4,000 impulses per minute.
3.The intensity of vibration shall visibly move the mass of concrete throughout a radi us of 18 inches (450 mm).
4.The Contractor shall provide a sufficient number of vibrators to properly consolidate each batch immediately after it is placed in the forms.
5.The Contractor shall have a tachometer available to check the speed of the vibrators.
d.Procedure: (1) Vibrators shall be manipulated so as to thoroughly work the concrete around the reinforcement and embedded fixtures and into the corners and angles of the forms.
2.The vibrators shall be inserted and withdrawn out of the concrete slowly. Contact with reinforcement shall be avoided.
e.The vibrations shall not cause segregation. Localized grout formation shall be avoided.
f.Application of vibrators shal l be at points uniformly spaced and not farther apart than twic e the radius over which the vibration is visibly effective.
g.Vibrations shall not be app lied directly to or through the reinforcement to sections or layers of concrete which have hardened to the degree that the concrete ceases to be plastic under vibration.
h.Vibrators shall not be used to move the concrete in the forms.
14.Successive pours: a. Preparation:
1.Immediately after placing concrete, all accumulations of mortar splashed on the reinforcement steel and the surfaces of forms shall be removed.
2.Dried mortar chips and dust shall be kept out of the plastic concrete.
3.Care shall be exercised in order not to injure or break the concrete-steel bond at and near the su rface of the concrete while cleaning the reinforcement steel.
4.When concrete placement is temporarily discontinued, the concrete shall be cleaned of laitance and other objectionable material to a sufficient depth to expose sound concrete.
5.To avoid visible joints at exposed faces, the top surface of the concrete adjacent to the forms shall be smoothed with a trowel.
6.If a "concrete wedge" might be produced at a construction joint, as in the sloped top surface of a wingwall, an insert shall be placed in the form to block out the wedge layer so that the placed concrete thickness is never less than 6 inches (150 mm). Concrete Construction 704.03 - 489 - b. Limitations:
1.Successive concrete pours can be made after the preceding pour is complete if the concrete compressive strength of the preceding pour has reached 2,000 psi (14 MPa).
c.Concrete shall not be placed in the superstructure until the substructure forms have been stripped and the concrete inspected for defects. The load of the superstructure shall not be allowed to bear on the substructure until its concrete has attained a compressive strength of 2,000 psi (14 MPa).
d.Cast-in-place concrete railings shall not be placed on concrete slab bridges until the falsework supporting the roadway slab has been released.
15.If any section of concrete is foun d defective, it shall be repaired or replaced, as directed by the Engi neer, at no additional cost to the Department.
16.Concreting in Cold Weather: a. The following requirements shall govern the placement of concrete when the ambient tem perature is less than 40°F (5°C):
1.The temperature of t he concrete shall not be less than 50°F (10°C) immediately after being placed.
2.The Contractor shall furnish heating equipment and/or enclose and protect the structure in su ch a way that the concrete and air surrounding it shall be maintained at a temperature between 50°F (10°C) and 100°F (38°C) for the first 72 hours after the concrete has been placed, and at a temperature between 40°F (5 °C) and 100°F (38°C) for the next 48 hours. The temperatur e of the air surrounding the concrete shall be gradually reduced to the outside air temp erature at a rate not faster than 5°F/h (2.8°C/h).
3.Curing moistu re shall be maintained.
4.The use of "salamander s" or other open flame heating units is prohibited. A shield shall be provided on heating equipment involving combustion so that no exposed metal will be in contact with the source of heat.
b.Insulated Forms:
1.The Contractor may us e form insulation to maintain concrete at the temperatures indica ted in Paragraph 14.a.(2) of this Subsection.
2.The temperature of the concrete at the time of mixing may be adjusted to assure that the temperature of the concrete will not exceed 100°F (38°C) due to the heat of hydration.
3.The insulated forms shall remain in place for 5 days. (4) The forms may be loosened slightly, if necessary, to control the temperature of the concrete below the maximum value specified. If loosening of the forms is necessary, prior approval of the Engineer must be obtained before the forms can be loosened.
704.03 Concrete Construction
- 490 - (5) When forms are to be removed after the specified 5 day period, the fall of the concrete temperat ure shall not be at a rate faster than 5°F (2.8°C) in any 1 hour.
6.The Engineer will use a digital thermometer with a thermocouple placed inside the fresh c oncrete to measure the concrete temperature. If a digital thermometer is not available, the Contractor shall provide four galvanized steel conduit tubes 1 inch (25 mm) in diameter and 12 inches (300 mm) long for each app lication of insulated forms. These tubes shall be provided with satisfactory rubber stoppers. The tubes shall be placed in the concrete as directed by the Engineer and shall be used to take the concrete's temperature. After curi ng is completed, the tubes shall be removed and the remaining holes shall be grouted.
i.The Contractor may provide a calibrated digital thermometer with a thermocouple for the Department's use.
c.Bridge Deck Curing in Cold Weather (1) The following requirements shall govern the placement of bridge deck concrete when the temperature will be less than 40 ⁰F during the 10-day wet curing period.
i.The temperature of the concrete shall not be less than 50⁰F immediately after being placed. (ii) The Contractor shall furnish heating equipment and/or enclose and protect the structure in su ch a way that the concrete shall be maintained at a temperature between 50 ⁰F and 100 ⁰F for the first 72 hours after the concrete has been placed, and at a temperature of between 40 ⁰F and 100⁰F for the next 168 hours. (iii) After 240 hours of curing is complete, the fall of the concrete temperature shall not be at a rate faster than 5 ⁰F/hour.
c.The Contractor shall assume all risk connected with the placing of concrete during cold weather, and permission given by the Engineer to place concrete during such time will in no way relieve the Contractor of the responsibility for satisfactory results. Any concrete showing damage from cold weather placement or curing shall be rejected.
17.Joints: a. Joints shall be square and normal to the forms; and bulkheads shall be provided for all, except horizontal, joints.
b.Construction joints shall not allow movement of abutting surfaces. They shall be made only where located in the contract or indicated in the placing diagram unless otherwise provided in these Specifications and approved by the Engineer.
c.Before depositing new concrete on or against concrete which has hardened, the forms shall be retightened and the concrete surface shall be thoroughly cleaned of foreign matter and laitance.
d.The placing of concrete shall be carried continuously from joint to joint. The face edges of all joints shall be carefully finished true to line and elevation. Concrete Construction 704.03 - 491 - e. Open Joints:
1.Open, expansion, and fixed joints; water stops; and bearing seats shall be constructed acco rding to the details shown in the contract.
2.Open joint templets shall be placed and removed without chipping or breaking the corners of the concrete.
3.When preformed, filled, ex pansion joints are specified, the material shall be placed in correct position as the concrete on one side of the joint is placed. When the form is removed, the concrete on the other side shall be placed.
4.The plates, angles, or other structural components of steel joints shall be accurately shaped at the shop to conform to the sections of the concrete floor.
5.Steel joints shall be maintained in the correct position when placing the concrete.
18.Concrete Surface Finish:
a.The Contractor shall finish all concrete surfaces, except bridge decks, in accordance with the requirements of this Section.
b.All formed concrete surfaces shall first be given an ordinary surface finish.
c.Ordinary Surface Finish: (1) Immediately following the removal of forms, all fins and irregular projections shall be removed from all surfaces.
2.Cavities produced by form ties and all other holes, honeycomb spots, broken corners or edges, and other defects shall be thoroughly cleaned, saturated with water, and then pointed and trued. The mortar shall be made from cement an d fine aggregate mixed in the same proportions as the concrete class being finished.
3.Mortar used in pointing shall be not more than 1 hour old. (4) The mortar patches shall be cured as described in this Subsection.
5.All construction and expansion joints in the completed work shall be left carefully tooled and free of all mortar and concrete.
6.The joint filler shall be left exposed for its full length with clean and true edges.
d.Surfaces requiring a rubbed finish are shown in the contract. e. A "grout-cleaned" surface finish will be considered an acceptable alternate to a rubbed finish. Concrete cast against steel forms or smooth, hard form liners, such as mas onite, metal, or fiberglass, may be given a "grout-cleaned" surface finish.
f.Concrete surfaces which are not to receive a rubbed finish shall be float-finished.
704.03 Concrete Construction
- 492 - g. Rubbed Finish:
1.For designated rubbed finish areas only, forms must be in place at least 12 hours, exclusive of time when the temperature is below 40°F (5°C), before they are removed to allow a rubbed surface finish. Forms must remain in place as described in Section 704.03 paragraph 7 on all other formed surfaces of the structure.
2.If forms are removed before curing is comple te to apply a rubbed surface finish, the concrete shall be kept wet while exposed.
3.When rubbing is completed, the surfaces shall be covered and the wet-cure resumed until a 72-hour wet-cure period is complete.
4.The concrete surface to be finished shall be saturated with water.
5.Rod holes and defects shall then be painted and allowed to set.
6.The surface shall be rubbed with a medium coarse carborundum stone using a small quantity of mortar on its face. The mortar shall be composed of cement and fine sand mixed in the proportions used in the concrete being finished.
7.Rubbing shall continue until all form marks, projections and irregularities have been removed, all voids are filled, and a uniform surface has been obtained.
8.The paste produced by this rubbing shall be left in place. (9) The final finish shall be obtained by rubbing with a fine carborundum stone and water. This rubbing shall be continued until the entire surface has a smooth te xture and uniform color.
10.After the final finish is completed and the surface has dried, it shall be rubbed with burlap to remove loose powder and shall be left free from all unsound patches, paste, powder, and objectionable marks.
h.Grout Cleaned Finish: (1) Surfaces to be grout cleaned shall be steel brushed to remove laitance and scale and to reveal partly obscured air bubble holes. Uneven form joints shall be ground smooth.
2.The surface shall be dampened and covered with an application of grout composed of 1 par t cement to 1.5 parts fine sand with sufficient water to produce a thick paint consistency.
3.Immediately after applicat ion of the grout, the surface shall be scoured with a cork float or other suitable material. This floating shall completely fill all holes and other irregularities in the surface.
4.When the grout is of such pl asticity that it will not be pulled from the holes, a float of sponge rubb er or burlap shall be used to remove excess grout.
5.When the grout is thoroughly dry, the surface shall be vigorously rubbed with dry burlap to completely remove any dried grout. No visible film of dry grout shall remain. Concrete Construction 704.03 - 493 - (6) Grout cleaning shall be done when the air temperature is at least 40°F (5°C) and rising. All cleaning on an area shall be completed the same day it is started.
7.Cement for grout cleaning shall be Type I with white Portland cement added as necessary to produce the desired color.
i.Floated Surface Finish: (1) Exposed concrete surfaces shall be struck off with a wooden template. Sufficient excess concrete shall be maintained ahead of the strike-off so that coarse aggr egate is forced below the surface.
2.The surface shall be thoroughly worked with a wooden float to produce a reasonably smooth, fine-grained surface.
3.Edges, corners, and joints shall be carefully finished by means of suitable edging tools.
19.Curing Concrete:
a.Exposed, unformed concrete surfaces which do not require a rubbed finish shall be wet-cured or membrane-cured.
b.Formed Concrete Surfaces:
1.Formed concrete surfaces will not require covering and curing until the forms are removed.
2.No additional covering or curing is required after the forms are removed if they were in place for at least 72 hours.
c.Unformed concrete surfaces which will receive a rubbed finish shall be wet-cured.
d.A wet-cure requires that immediately after finishing, the exposed concrete be covered with a double thickness of wet burlap, which shall be kept saturated for at least 72 hours.
e.Membrane Curing:
1.Membrane curing requires that immediately after finishing, the exposed concrete shall be sprayed with a continuous, uniform coating of white pigmented, membrane-forming cu ring compound. The application shall be uniform and applied at a rate no less than 1 Gal/200 SF (0.2 L/m²).
2.Curing compound shall not be applied to construction joints, reinforcing steel, or surfaces which are to receive a rubbed finish. Any compounds applied to such surfaces or items shall be removed by blast cleaning.
3.The curing membrane shall be protected and maintained throughout the 72-hour curing period. Any damage to the membrane during this period shall be immediately repaired.
20.Benchmarks: a. This work shall consist of installing Department furnished benchmarks on structures. The benchmarks shall be installed near the right corner of abutment No. 1 on the horizont al portion of the top of the concrete barrier rail. The Contractor shall cast the benchmark into the concrete so its perimeter is flush with the finished surf ace and the top is above the surface. Recessed installations are not acceptable.
704.03 Concrete Construction
- 494 - b. The benchmark is a circular, 2 inch (50 mm) diameter, solid brass marker with a slightly domed head and a 2 inch (50 mm) long ribbed shank. The Contractor shall obtain th e benchmarks at the District Office. The Department will stamp the benchmar k with the required information.
21.Preparation of Existing Structures: a. When the contract provide fo r using any part of the existing concrete or masonry bridge or structure in the new bridge or structure, only those portions shall be removed which are so indicated in the contract. The connecting edges of the existing structure shall be cut, chipped, and trimmed to the required lines and grades without weakening or damaging that part of the structure to be retained. All ex isting reinforcing steel which is encountered shall be cleaned, straight ened, and extended into the new work as shown in the contract.
b.When part or all of an existing bridge deck is to be removed, the removal operation shall be perfo rmed without damage to the girders or any portion of the structure to be retained.
c.The term damage to the gird ers is defined as, but not limited to, the following:
1.For concrete girders – spalling or cracking of the girder or damaging the existing reinforcing steel which projects from the top of the girder.
2.For steel girders – punching through or denting/distorting the top flange, damaging the flange to web weld or damaging the shear connectors that project from the top of the girder.
d.At least 10 working days prior to the deck removal operation, the Contractor shall submit to the Engineer details of the removal operations showing the methods, sequence of removal and equipment to be used.
e.At the beginning of the remova l operation, the Contractor shall demonstrate to the Engineer that the removal operation is acceptable by removing a 10 feet long x 4 feet wide (3 m x 1.2 m) section of the deck, over the top of a girder. If the gi rder or any other portion of the structure that is to remain in place has not been damaged, the Contractor may continue. If the Engineer determines that damage has bee n done or is likely to occur, the Contractor shall alter the removal operation.
f.Any damage to the girders, reinforcement or shear connectors that occurs during the trial demonstratio n shall be repaired as directed by the Engineer at no additional co st to the Department.
g.Any isolated or accidental damage that occurs during the removal operation shall be repaired as directed by the Engineer at no additional cost to the Department.
h.Should a girder sustain dam age, which in the opinion of the Engineer renders it unfit to remain in place, it shall be replaced at no additional cost to the Department.
22.The Contractor shall paint a ll exposed metal, except weathering grade steel, as described in Section 709. Concrete Construction 704.04 - 495 - 23. Barrier Curbs and Rails:
a.Concrete barrier curbs and bridge rails shall present a smooth, uniform appearance conforming to the horizontal and vertical lines shown in the contract or as directed by the Engineer, and shall be free of lumps, sags, or other irregularities.
b.The top and visible edges of barrier curbs and rails shall not vary more than 1/4 inch (6 mm) from the edge of a 10 foot (3 m) straightedge, and the front and back faces shall not vary more than 1/2 inch (13 mm) from the edge of a 10 foot (3 m) straightedge. Area s not conforming to the above requirements shall be removed and replaced by the Contractor at no additional cost to the Department.
24.Protective System for Bri dges with Weathering Steel Girders
a.It is the responsibility of t he Contractor to protect the exposed faces of abutments, piers and MSE wa lls from staining caused by runoff from the weathering steel superstructu re. Acceptable methods of protection which may be used are:
1.Before steel girders are set, the exposed face of the abutments and the top ten fe et (three meters) of the piers and the MSE walls directly under the bridge shall be wrapped with 6 mil (0.15 mm) polyethylene to protect against staining. The polyethy lene wrap shall remain in place until after the bridge deck is poured. When the wrap is removed, concrete surfaces of abutments, piers and MSE wa lls shall be cleaned of any stains from the weathering steel.
2.As an alternate, a stain resisting coating may be used in place of the polyethylene wrap. The stai n resisting coating shall be applied to the exposed face of the abutments a nd the top ten feet (three meters) of the piers and the MSE walls directly un der the bridge. The stain resisting coating shall be applied to the concrete surfaces prior to erecting the steel superstructure.
b.Preparation of the concrete surface and mixing and applying the coating shall be in accordance with the manufacturer’s instructions. Minor appearance inconsistencies resu lting from application of stain resistant coating s hall be acceptable.
c.After the bridge deck is poured, concrete surfaces of the abutments, piers and MSE walls shall be cleaned of any stains from the weathering steel.
704.04 Method of Measurement
1.The quantity of concrete for which payment will be made shall be computed by the Department in cubic yards (cubic meters) from dimensions shown in the contract. No field measurement is required. Pay quantities are those shown in the contract.
2.When shown in the bid proposal Schedule of Items, the seal course concrete quantity will be measured in cubic yards (cubic meters) of concrete placed within a volume bounded by vertical planes 18 inches (450 mm) outside and parallel to t he limits of the footings.
704.04 Concrete Construction
- 496 - 3. When seal course concrete is not shown in the bid proposal Schedule of Items, it shall be paid for as “extra work” when it is necessary to stop unforeseen water intrusion.
4.Calculations:
a.The volume involved in fillets, scorings, and chamfers 1 square inch (645 mm2) or less in cross sectional area shall be neglected.
b.The concrete plan quantity ac counts for the volume of precast or cast-in-place concrete piles or pipe piles encased in the concrete.
c.No deductions shall be made for the volume of concrete displaced by steel reinforcement, H-pile, floor drains, or expansion joint material.
d.Box Culverts: (1) The Department will compute the quantity of concrete for box culverts based on the cross-sectional area of the culvert's walls times the centerline length of the culvert.
2.An additional allowance is made for concrete box culverts constructed with either a horizontal or vertical break in barrel alignment.
3.The additional allowance for each break in alignment shall be calculated by measuring the inside perimeter of the nominal box opening in feet (meters), then dropping the uni ts (feet) (meters) and multiplying the unit-less perimeter measurement times 0.05 cubic yards (0.125 cubic meters).
5."Preparation of Bridge _____" is measured by the Each (ea) or Square Yard (SY) [Square Meter (m 2)].
704.05 Basis of Payment 1. P a y I t e m P a y U n i t
Class _____ Concrete for ________ Cubic Yards (CY) [ C u b i c M e t e r s ( m 3)] Seal Course Concrete Cubic Yards (CY) [ C u b i c M e t e r s ( m3)] Preparation of Bridge _____ Each (ea) Square Yard (SY) [Square Meter (m2)]
2.All costs for concrete rails shall be included in the appropriate concrete and reinforcing steel pay items for the structure.
3.The seal course concrete shall not be thicker than 9 inches (225 mm), and any concrete placed in excess of 9 inches (225 mm) deep will be done at no additional cost to the Department. Seal course excavation is subsidiary to the seal course concrete.
4.All costs associated with obta ining benchmarks from the District Office and installing them shall not be measured for payment but shall be considered subsidiary to the items for which direct payment is provided.
5.Concrete curing shall be considered as subsidiary to the concrete construction. Concrete Construction 704.05 - 497 - 6. Furnishing, placing, and grouting bars for rock anchors is subsidiary to the concrete bid item for the structure.
7.The construction of weep holes is subsidiary to the concrete bid item for the structure.
8.Payment Deductions:
a.The 28-day compressive strength is determined by the average strength of all cylinders made on a specific day to determine the 28- day compressive strength of all of a group’s class of concrete poured that day. Concrete with a 28-day compre ssive strength not meeting the design compressive strength is subject to removal.
b.If the 28-day compressive strength is less than the design compressive strength, cores may be take n, at the discretion of the Engineer, within 45 days after the concrete was placed. The average of the cores will be used to determine the compressive strength.
c.If either the 28-day compressive strength or the average core strength is less than the design strength and the En gineer determines that the concrete is acceptable for use, the concrete is subject to a payment deduction. The pay deduction is shown below: 2 x (Design Compressive Strength - 28-day Compressive Strength) Design Compressive Strength = Percent Reduction Or 2 x (Design Compressive Strength - Av erage Core Compressive Strength) Design Compressive Strength = Percent Reduction
9.The polyethylene wrap or stain resisting coating will not be paid for directly, but shall be subsidiary to the item “Class ____ Concrete for ____”.
10.Payment is full compensation for all work described in this Section. - 498 - SECTION 705 -- PRECAST OR PRECAST/PRESTRESSED CONCRETE STRUCTURAL UNITS
705.01 Description
1.This work consists of all labor, materials, and equip ment required in the production of Precast or Prec ast/Prestressed Structural Units.
2.The contract shall be supplemented by Contractor-provided working drawings submitted in accordance with Subsection 105.02.
705.02 Material Requirements
1.The materials used shall meet the requirements described in Table 705.01. Table 705.01 Material Requirements Applicable Material Section Concrete .......................................... .1002 Admixtures ....................................... .1007 Water 1005 Fine Aggreg ate ................................ .1033 Course Aggr egate ............................ .1033 Fly Ash 1008 Spiral Reinforc ing Wire .................... .1023 Prestressed Steel Strand ................. .1026 Post-Tensioning Assembly Steel ..... .1025
2.The concrete class used in the manufacture of Precast or Precast/Prestressed Structural Units shall be shown in the contract.
3.The Contractor shall be responsible for the concrete mix design. Concrete mix designs shall be proportioned in accordance with ACI Standard 318 and the following additional requirements:
a.The mix designs or change to a mix design shall be submitted for approval to the Engineer 4 weeks before beginning any concrete work. Refer to Table 705.03 for required testing for any mix design.
b.Concrete shall consist of Type I, Type II, or Type III Portland cement, aggregate, air-entraining admixture, and water. Concrete may also contain Class C or Class F fly ash, slag cement or Silica Fume and ASTM C 494 approved Type A, Type B, Type D, and Type F admixtures.
c.No change shall be made in the approved concrete mix design during the progress of the work without the prior written permission of the Engineer.
4.Reinforcement shall be furnis hed, handled, stored, and placed in accordance with the requirements of Section 707.
5.Welding of reinforcing steel is prohibited unless specifically authorized by the Engineer.
6.Prestressing steel other than t hat specified in the contract may be furnished with the approval of the Engineer. The yield and ultimate strength and other pertinent characteristics of this steel shall be submitted to the Engineer.
Source: Nebraska Standard Specifications for Highway Construction, 2017 Edition. Pages 513–531 of 1,048.