2403.04 PROPORTIONS FOR LIGHTWEIGHT STRUCTURAL CONCRETE.
When lightweight concrete is specified, the aggregate quality, proportions, mixture characteristics, and controls will be included in the contract documents.

2403.05 EQUIPMENT GENERAL.
Equipment shall meet requirements of Section 2001 and the following articles:

A. Weighing and Proportioning Equipment.
Article 2001.20 shall apply.

B. Mixing Equipment.
Article 2001.21 shall apply.

C. Bins.
Article 2001.06 shall apply.

D. Field Laboratory or Field Office.
Section 2520 shall apply.

2403.06 PROPORTIONING AND MIXING OF CONCRETE.
The respective paragraphs of Article 2301.13 shall apply regarding storage and handling of cement, fly ash, aggregates, measurement of materials, and ready mixed concrete, except for the truck dumping area required in Article 2301.13, A, 1.

A. Mixing of Materials.
Materials shall be thoroughly mixed in an approved mixer at the site of placement or by an approved ready mix plant. The Engineer may withhold approval of use of ready mixed concrete from any plant which has a previous record of unsatisfactory performance.

B. Concrete Mixed on the Site.
Materials mixed in approved mixers at the site of placement shall be mixed in accordance with the specific requirements for the equipment used. The mixing capacity shall be such that finishing operations can proceed at a steady pace with final finishing completed before concrete starts its initial set.

Concrete, as discharged from the mixer, shall be uniform in composition and consistency. Each batch of concrete shall be thoroughly discharged from the mixer before the next batch is introduced. Upon cessation of mixing for any considerable length of time, the mixer shall be thoroughly cleaned and flushed with water.

C. Heating Aggregates.
When aggregates are heated, they shall be heated and handled to avoid damage by overheating and to insure uniform moisture content of aggregate entering the mixer. Aggregates may be heated by steam pipes or coils through aggregate piles. Aggregates shall not be heated by direct, dry heat unless they are mechanically agitated during the heating process.

2403.07 PLACING AND FINISHING EQUIPMENT.
Equipment for placing and finishing concrete shall comply with the following requirements:

A. Above Water or Dry Placement Equipment.

1. Tremies.
When required, a tremie shall be used for depositing concrete in the dry. It shall not be more than 12 inches (300 mm) in diameter and there shall be no aluminum parts in contact with the concrete. The length shall be sufficient to extend to the bottom of the placement area.

2. Chutes.
Chutes for depositing concrete shall be constructed of metal or with a metal lining. Aluminum shall not be allowed to be in contact with the concrete. The length shall be sufficient for the delivery point to be as close as possible to the point of deposit, and provide a slope to allow the concrete to flow slowly without segregation.

B. Underwater Placement Equipment.
Concrete placed under water shall be placed with a tremie, pump, or other equipment which meets the approval of the Engineer.

A tremie used to deposit concrete under water shall be constructed to be water tight and readily discharge concrete. The tremie shall not be more than 12 inches (300 mm) in diameter and there shall be no aluminum parts in contact with concrete. The discharge end of the tremie shall be constructed to prevent water intrusion and permit free flow of concrete during placement operations. It shall have sufficient weight (mass) and length to rest on the bottom of the placement area prior to start of concrete placement. The tremie shall be supported so that it can be raised or lowered to increase or reduce the discharge of concrete.

C. Consolidation.
All concrete for box and arch culverts, bridge substructures, bridge decks, and bridge deck overlays shall be vibrated by vibrating units. All vibrators shall be operated at speeds not less than 3,500 vibrations per minute. Adequate vibration equipment shall be provided to avoid delays due to breakdown. The number of vibrating units shall be sufficient to properly consolidate the concrete placed.

When consolidating concrete reinforced with epoxy coated bars, vibrator heads covered with rubber or other resilient material approved for consolidation shall be used.

D. Heating and Protection Equipment.
Whenever heating is done, the following requirements shall be met: The attendant shall be equipped with not less than one non-freezing fire extinguisher of adequate capacity. Any heating equipment involving combustion in or near the space to be heated shall be adequately supported, anchored, and guyed to prevent movement or overturning. Use of a salamander or other type of open flame heating unit is prohibited. Heating equipment shall be constructed with a shield so that metal in direct contact with the open flame is not exposed.

E. Forms.
Material used for forms shall be metal, surfaced lumber, plywood, masonite, hard pressed composition board, or other approved material backed by suitable studding, walers, etc. It shall be free from knotholes, cracks, splits, warps, or other defects which would prevent it from producing the strength, accuracy, and appearance necessary in the finished concrete surface. Forms shall be constructed with mortar tight joints and of material sufficient in strength to hold concrete without bulging between supports.

Forms shall be designed for strength as specified in Article 2403.17. Wood forms for all exposed surfaces, except wingwalls parallel to the culvert barrel, headwalls, and such portions as may be completely covered by a single board, shall be lined with metal, plywood, fiberglass, or hard pressed water resistant composition board not less than 3/16 inch (5 mm) thick. All forms shall be in good condition. Joints in the lining shall be mortar tight and smoothly cut and shall break joints with the form lumber. Small irregular areas may be formed with lumber against concrete to be rubbed, provided there is no joint in lumber used on any flat surface of concrete except at angles, ribs, bevels, molding, etc., where there is a juncture between two surfaces. Blocks, ribs, bevels, moldings, etc., for ornamental effect on lined surfaces shall be placed inside the lining. Forms shall be designed and constructed so that they may be removed without damage to the concrete. Blocks and bracing shall be removed with the forms, and in no case shall any portion of wood forms be left in the concrete. Forms shall be constructed so that the finished concrete shall be of the form and dimensions shown in the contract documents and true to line and grade. Forms shall be filleted 3/4 inch (20 mm) at all sharp corners (90 degrees or sharper) and should be given a draft in the case of all projections, such as girders, copings, etc., sufficient to insure their easy removal. Ties and bracing must be sufficient to support the expected load. When forms appear to be insufficiently braced or unsatisfactorily constructed either prior to or during placement of concrete, the Engineer shall order the work stopped until the defects have been corrected.

Forms shall be coated with an approved form release agent prior to the placement of concrete. Forms shall be thoroughly wetted with water immediately prior to concrete placement. Reused form material shall be thoroughly cleaned and shall be free of bulges, splits, warps, or bends.

Stay-in-place forms shall be used only when specified in the contract documents.

2403.08 PLACING CONCRETE.
Concrete mixed at the site of the work shall be placed immediately after mixing. Ready mixed concrete shall be placed as soon as practical after delivery, but in all cases within the specified time limit for the equipment used for delivery.

Concrete shall be placed in a manner which will avoid segregation or separation of the ingredients. In placing concrete, all the following precautions shall be observed:

A. In handling concrete from the mixer to the place of deposit, care shall be taken to avoid segregation.

B. When concrete is deposited through a chute, the slope of the chute shall be sloped to allow concrete to flow slowly without segregation. The delivery point of the chute shall be as close as possible to the point of deposit. Chutes and spouts shall be kept clean. They shall be thoroughly flushed with water before and after each run, and the water shall be discharged outside the forms.

Concrete shall not be pumped through aluminum conduit or tubing.

C. A tremie is not required when filling steel shell piles or encasing steel H-piles, but a tremie shall be used whenever the distance through which other concrete must be dropped vertically exceeds 6 feet (2 m), except a 3 foot (1 m) drop shall not be exceeded for bridge floors and culvert slabs. A tremie will not be required for concrete placement of elements which have a maximum dimension no greater than 12 inches (300 mm) provided that the following Part D is adhered to and concrete is placed in lifts.

D. Concrete shall not be deposited in large quantities at a single point and then caused to flow along inside the forms.

E. In depositing concrete, care shall be taken to entirely fill the form without bulging the form or disturbing its alignment.

F. Concrete shall be manipulated and vibrated in a manner to bring a thick layer of mortar into contact with forms and reinforcement and to prevent formation of pockets of coarse aggregate.

G. Concrete shall not be placed in flowing water within the area of a footing. Such flowing water shall be controlled in pipes or trenches outside the forms. In extreme cases, a seal course may be ordered to overcome this difficulty.

H. Structural Concrete placed when the air temperature is at or below 40°F (4°C) shall be protected as provided in Article 2403.11.

An adequate supply of water suitable for washing testing equipment shall be maintained at a convenient location, as directed by the Engineer, near the site of concrete placing operations.

When concrete is being placed during cold weather, the Contractor shall provide an approved, conveniently located shelter, suitable for use in performing on the site tests of the concrete being placed. The shelter shall have a cover, shall be enclosed on at least three sides, and shall be placed to provide maximum protection from the weather.

2403.09 VIBRATION OF CONCRETE.
Vibrators shall be manipulated through all available space in the mass of concrete with particular attention to corners and faces of concrete against forms and joints. Care shall be used to prevent the vibrator from penetrating any portion of previously set concrete.

Vibration shall be applied to each batch of concrete as it is placed in the forms. It shall settle and thoroughly consolidate the concrete into close contact with the forms, reinforcement, and previously placed concrete, but shall not be continued to cause segregation or to the extent that localized areas of grout are formed. The operations of placing and consolidating shall be conducted so that the resultant concrete, upon removal of forms, is smooth and dense, free from all honeycomb or pockets of segregated aggregate.

Forms shall be designed to withstand effects of vibration without appreciable distortion from the desired shape or position.

2403.10 PROTECTION AND CURING OF CONCRETE.
Concrete which has been placed shall be protected from external stress between the time it ceases to be plastic and the time it may be stressed, as provided in Article 2403.19.

Runways for transporting materials over concrete floors less than 7 calendar days old shall be supported directly over structural members or over piers or abutments, so the concrete in the floor is subjected to compressive stress only.

Runways built over portions of formed but unpoured floors shall be supported on floor forms or beams.

Unless concrete is protected as specified in Article 2403.11, exposed surfaces, including surfaces from which forms have been removed less than 60 hours after the concrete has been placed, shall be protected in the following manner for at least 4 calendar days after concrete is placed: Immediately after any required finishing operations are completed, the surface shall be coated with white pigmented curing compound, meeting requirements of Article 4105.05, applied at a rate of not more than 135 square feet per gallon (3.3 m²/L). As alternatives, the surfaces may be covered with paper or plastic film, meeting requirements of Section 4106, or the surface may be covered with burlap, straw, or sand and shall be kept continuously wet.

White pigmented curing compound shall not be used on surfaces against which concrete is to be placed or which are to receive a sealer. When the Contractor elects to use white pigmented curing compound on any part of an integral unit, the Engineer may require use of the curing compound on adjacent areas of such integral unit, so that each pier, abutment, or other surface visible after construction presents a uniform and pleasing appearance.

Concrete floors shall be cured as provided in Article 2412.07.

Barrier railing shall be cured as provided in Article 2414.02.

2403.11 PLACING AND PROTECTION IN COLD WEATHER.
Concrete shall not be placed, without specific notice to the Engineer, when the air temperature is at or below 40°F (4°C).

Frozen materials shall not be used in the concrete. Concrete shall not be placed against frozen forms, earth, or rock or against other concrete having a temperature below 40°F (4°C).

In addition to protecting the concrete against chilling or freezing, the Contractor shall heat the water or aggregates or both so that, when placed, the concrete will have a temperature appropriate for the mass and dimensions of the portion of the structure being placed, but not less than 45°F (7°C) or more than 80°F (27°C).

Before concrete is placed at ambient air temperatures below 40°F (4°C) or when these temperatures might occur during the protection period, the Contractor shall have provided heating or protecting facilities or both meeting requirements of Article 2403.07, D, adequate to protect the work as follows:

The concrete shall be maintained at a temperature of not less than 50°F (10°C) for the first 48 hours after placing. The temperature of the concrete shall then be gradually reduced at a rate not exceeding 25°F (15°C) in 24 hours. When heating and housing is used, temperature monitors shall be located in the concrete at the furthest and closest point from the heat source. The maximum temperature of the monitor point closest to the heat source shall not exceed 150°F (65°C).

In lieu of protection involving housing and heating, the Contractor may protect concrete by the use of forms insulated with a commercial insulating material adequate to maintain the concrete temperature at not less than 50°F (10°C) for the first 48 hours after placing. These insulated forms shall be left undisturbed for the next 48 hours, after which they may be removed. When forms are insulated, exposed horizontal surfaces shall be protected with a similar layer of the insulating material or an adequate layer of hay or straw, properly secured.

Suitable provision, including cast-in-wells for thermometers, shall be made to provide a means for determining the temperature of the concrete.

Whenever heating is done, combustible material shall be firmly secured to prevent contact with any source of heat, and adequate precautions shall be taken to prevent fires.

If all the concrete is at least 1 foot (0.3 m) below ground water level, it may be placed at a temperature not less that 40°F (4°C) and flooded to a minimum depth of 1 foot (0.3 m) in lieu of other methods of protection and curing, with the provision that concrete cured in this manner may not be subjected to freezing temperature within 10 calendar days after it is placed. In lieu of flooding, culvert footings may be protected from freezing by an adequate layer of straw or hay for at least 5 calendar days.

2403.12 PLACING LARGE VOLUMES OF CONCRETE.
Whenever the volume is too great to be placed in one continuous operation, the work shall be subdivided as shown in the contract documents or as directed by the Engineer.

2403.13 BONDING CONSTRUCTION JOINTS.
When placing of concrete in any section of a structure must be interrupted, the construction joint shall be located as specified in Article 2403.20. The surface of the concrete in horizontal joints, except in the area near the form, shall be left rough to increase the bond with concrete that is to be placed later. The top surface of the concrete adjacent to the forms shall be finished to a horizontal 3/4 inch (20 mm) bevel strip. Keyways shall be embedded not less than 1 1/2 inches by 3 inches (35 mm by 75 mm) into the surface of the concrete. Tapered sections, which would otherwise result in a feather edge, shall be formed by an insert so that the succeeding layer of concrete will end in a section not less than 6 inches (150 mm) thick. In addition to the key notches in concrete that is not reinforced, steel dowels not smaller than 3/4 inch (20 mm) shall be set around the edge of the section at intervals not greater than 2 feet (0.6 m). The dowels shall project at least 1 foot (0.3 m) on each side of the joint.

2403.14 BONDING NEW AND OLD WORK.
When new concrete is to be placed in contact with old concrete or with concrete that has hardened, the surface of the existing concrete shall be thoroughly cleaned of all laitance, loose particles of concrete, dirt, or other foreign materials, by sandblasting followed by an air blast. Forms shall then be placed against the old concrete, using care to avoid contamination of the cleaned surface. Fresh concrete shall then be placed against the clean, dry surface and thoroughly consolidated to insure a tight joint and a good bond.

Bonding agent may be required as specified in the contract documents.

2403.15 DISPLACING WATER WITH CONCRETE.
Concrete shall not be placed into or under flowing water. Concrete may be placed in still water only under the following conditions and under the supervision of the Engineer.

A. If water courses and sumps are provided outside the area over which concrete is to be placed and it is demonstrated that the water elevation can be controlled to an elevation at or near the elevation of the bottom of the concrete to be placed to the extent that there is no appreciable or objectionable flow across said area, the Contractor will be permitted to place the concrete starting at a point most removed from the sumps and progressing toward the sumps, shoving and displacing water as the placement progresses. The water elevation within the forms at the start of placing shall be maintained at substantially the same elevation through the pour. This may be accomplished by bailing or pumping. Direct pumping from inside the forms will not be permitted in excess of the pumping necessary to remove only the quantity of water displaced by concrete.

If there are required excavations or trenches within the area, the bottoms of which are below the general elevation of the area, and if it is impossible or impractical to provide gravity drainage to the sumps, the Contractor may be permitted to slowly displace the entrapped water with the concrete during placement. The Contractor may be required to bail or otherwise dewater the trench immediately prior to or during the placement. A prerequisite to placing concrete in excavations or trenches shall be that the depth of water shall not appreciably exceed 30% of the depth of concrete being placed.

B. If other methods for the placement of seal courses are not provided in the contract documents, they shall be placed in the following manner:

When possible, seal courses shall be placed in one continuous operation. Concrete shall be placed to approximately the required depth, progressing from one end over the entire area in such a manner that the volume of concrete will be gradually expanded without dropping the concrete through water and with the minimum amount of agitation. The surface of the seal course shall be approximately level. Sumps or depressions for pumping out the water shall be placed outside the area of the footing.

Concrete shall be placed with equipment described in Article 2403.07, B. In operating a tremie, the tremie shall be kept filled at all times, and the discharge end shall be raised only an amount sufficient to permit the concrete to be discharged.

When pile encasements are placed by use of a tremie and the bottom of the encasement is below the controlled water level, drain holes not less than 1 inch (25 mm) in diameter shall be provided in the encasement form at intervals of 1 foot, 2 feet, and 3 feet (0.3 m, 0.6 m, and 0.9 m) above the controlled water elevation. The rate of concrete placement in this area shall be so that no free water is entrapped inside the form above the top drain hole.

2403.16 LAITANCE.
All laitance shall be removed from the surface of seal courses before the footing is placed. Care shall be used in placing of other concrete to prevent formation of laitance on the surface of the concrete. All laitance shall be entirely removed by means of shovels, stiff wire brooms, or by other suitable methods before the succeeding layer of concrete is placed.

2403.17 DESIGN AND CONSTRUCTION OF FORMS AND FALSEWORK.
Materials for forms and falsework may be either new or used. It is the Contractor's responsibility to ensure that all materials are suitable for the use intended. All material which the Engineer determines to be damaged, defective, or otherwise unsuitable will be rejected.

All falsework plans shall be designed and certified by a Professional Engineer licensed in the State of Iowa.

A. Construction of Forms.
Materials and construction of forms in direct contact with concrete shall be as specified in Article 2403.07. Forms for walls or columns shall have studs, wales, and ties designed to withstand the maximum fluid pressure discussed below. Prefabricated form systems shall be certified for the expected pressures. Forms for walls and columns shall be guyed, shored, and/or braced to withstand wind loads and to prevent alignment shift resulting from construction live load.

B. Construction of Falsework.
Falsework for supporting construction of reinforced concrete superstructures, reinforced beams, and cantilevers of substructures, shall be built on foundations of sufficient strength to carry the loads safely and without significant deflection. Ample falsework piling shall be driven to support all falsework which cannot be founded on rock, shale, thick deposits of compact gravels, coarse sand, or the firm clays in natural beds. On the soils materials listed above, mudsills or other spread footings may be used, and they shall be of a size to be determined considering the applied loads and the bearing value of the soil. Bearing values of all piles used to support falsework shall be determined as provided in Section 2501 and shall be at least equal to the applied loads.

Pile bents exceeding 10 feet (3 m) in height shall be sway braced transversely to resist lateral loads. Pile bents exceeding 10 feet (3 m) in height shall be longitudinally braced to resist construction live loads, unless the bents are secured to longitudinal members which are secured against longitudinal movement. Bracing and connections shall be shown on falsework plans. Adequacy of bracing and connections will be reviewed by the Engineer.

Pile caps shall be secured to each pile. Blocks, wedges, and jacks for height adjustment shall be secure and stable, and they shall be reviewed by the Engineer before concrete placement. Transverse joists shall be held against individual collapse. Longitudinal stringers shall have a positive spreader system over each support.

Continuous members shall be secured against uplift from unbalanced concrete placement. Concrete shall be placed in a manner which will minimize unequal loads on hanger legs.

C. Design Loads.
Formwork and falsework shall be designed for the following loads:

1. Vertical load of concrete with a density of 150 pounds per cubic foot (2400 kg/m³).

2. Horizontal load of fresh concrete as a liquid with a density of 150 pounds per cubic foot (2400 kg/m³) for the depth of plastic concrete.

3. Vertical load of forms and falsework.

4. Construction live load equal to 50 pounds per square foot (2.4 kPa) of horizontal projection.

5. Wind loads on walls and columns shall be in accordance with requirements of the ACI.

D. Design Stresses.
Formwork and falsework shall be designed using working stresses and a normal duration of load, as for a permanent structure. Lumber strength shall be calculated on the basis of dressed size and, except for sheathing, a dry condition. Publications of the ACI and the National Forest Products Association will be considered standard references for design and analysis of timber falsework.

Unsupported length of wooden columns and compression members shall not exceed 50 times the dimension of the least side. In addition, the member shall be subject to analysis as a column.

Unless the Contractor certifies a higher stress grade or value, adequacy of falsework material will be checked on the basis of the following values:

1. Structural steel stresses per AASHTO for 30,000 psi (207 MPa) yield strength and 22,500 psi (155 MPa) maximum working stress.

2. Plywood sheathing stresses per American Plywood Association for concrete form grade, Class I, wet use, permanent loading, span-perpendicular-to-face grain. Orientation of plywood panels must be shown on drawings if advantage is taken of greater strength with span-parallel-to-face grain.

3. Stresses for lumber 4 inches (100 mm) or less in thickness, in psi (MPa) as follows:

fb, bending	= 1000 (6.90)
ft, tension	= 625 (4.30)
fv, shear	= 120 (0.83)
fc, perpendicular to grain	= 345 (2.40)
fc, parallel to grain	= 1050 (7.20)
E, modulus	= 1,500,000 (10,300)

4. Stresses for lumber 5 inches (125 mm) thick and thicker in psi (MPs) as follows:

fb, bending	= 1200 (8.30)
ft, tension	= 1000 (6.90)
fv, shear	= 120 (0.83)
fc, perpendicular to grain	= 390 (2.70)
fc, parallel to grain	= 1000 (6.90)
E, modulus	= 1,600,000 (11,000)

5. Safe bearing value of coarse sand, gravel, very firm clay, and other similar confined soils in thick beds at 1500 pounds per square foot (72 kPa) unless otherwise recommended by a Professional Engineer licensed in the State of Iowa. Safe bearing value of compacted berms at 1 ton per square foot (96 kPa).

E. Deflection.
Falsework for slab and girder bridges shall provide for slight settlements, deformations of members, crushing, and closing of joints. Sag in excess of 1 inch (25 mm) or 1/800 of the span length, whichever is greater, in the soffit of a girder or slab may be cause for rejection.

Deflection of sheathing and joists shall be limited to 1/360 of the span length. Deflection of falsework stringers shall be calculated, and screed guides shall be adjusted to compensate.

F. Falsework Plans.
The Contractor shall submit plans for falsework and centering on all concrete slab and cast-in-place concrete girder bridges in accordance with Article 1105.03. Submittal of forming details for bridge decks on concrete beam and steel beam bridges is not required unless specified in the contract documents. In addition, calculations or evidence of adequacy may be required by the Engineer. Revised plans may be required by the Engineer later because of unforeseen site conditions, unusual construction procedures, or deviation from original falsework plans.