DEPOSITING CONCRETE 1.14.1 GENERAL (2000)

Before beginning placement of concrete, hardened concrete and foreign materials shall be removed from the inner surfaces of the mixing and conveying equipment. Before depositing any concrete all debris shall be removed from the space to be occupied by the concrete, and mortar splashed upon the reinforcement and surfaces of forms shall be removed. Reinforcement shall be checked for position and fastening and approval of the Engineer obtained. Where concrete is to be placed on a rock foundation, all loose rock, clay, mud, etc., shall be removed from the surface of the rock. Any unusual conditions or excess fissures shall be treated as directed by the Engineer. Water shall be removed from the space to be occupied by the concrete before concrete is deposited, unless otherwise directed by the Engineer. Any flow of water into an excavation shall be diverted through proper side drains to a sump, or be removed by other approved methods which will avoid washing the freshly deposited concrete. If directed by the Engineer water ventpipes and drains shall be filled by grouting or otherwise after the concrete has thoroughly hardened. All temporary runways for delivery of concrete must be supported free from all reinforcing steel. The supervisor of the concrete placing crew shall maintain certification by the American Concrete Institute as a Concrete Flatwork Finisher, or Concrete Transportation Construction Inspector.

1.14.2 HANDLING AND PLACING (1993)

a. Concrete shall be handled from the mixer, or in case of ready-mixed concrete, from the transporting vehicle, to the place of final deposit as rapidly as practicable by methods which will prevent the separation or loss of the ingredients. Special care shall be taken to fill each part of the forms by depositing concrete as near final position as possible, to work the coarser aggregates back from the face and to force the concrete under and around the reinforcement without displacing it. Concrete shall not have a free fall of more than 4 feet unless permitted by the Engineer. Depositing a large quantity at any point and working it to final position, shall not be permitted.

b. Concrete shall be placed in horizontal layers and each layer shall be placed and compacted before the preceding layer has taken initial set so as to prevent formation of a joint. It shall be so deposited as to maintain, until the completion of the unit, a plastic surface approximately horizontal, except in arch rings. Temporary struts or braces within the form shall be removed when concrete has reached an elevation rendering their further service unnecessary. These temporary members shall be entirely removed from the forms and not buried in the concrete. 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 the projecting reinforcement. Under no circumstances shall concrete that has partially hardened be deposited in the work.

c. In placing concrete for an arch ring, the work shall be carried on symmetrically with respect to the center line, and the working faces of the completed courses shall be on approximately radial planes. This requirement applies whether or not the arch is placed in voussoir sections with allowance for key sections for final placement.

d. In order to allow for shrinkage or settlement, at least 2 hours shall elapse after placing concrete in walls, columns or stems of deep T-beams before depositing concrete in girders, beams or slabs supported thereon, unless otherwise specified or shown on the plans. If the columns are structural steel encased in concrete, the lapse of time to allow for shrinkage or settlement need not be observed.

e. Concrete in girders, slabs and shallow T-beam construction shall be placed in one continuous operation for each span, unless otherwise provided. Concrete shall be deposited uniformly for the full length of the span and brought up evenly in horizontal layers.

f. No concrete shall be placed in the superstructure until the pier forms have been stripped sufficiently to determine the character of the concrete in the piers, and the load of the superstructure shall not be allowed to come upon abutments, piers and column bents until they have been in place at least 7 days, unless otherwise permitted by the Engineer.

1.14.3 CHUTING (1993)

When concrete is conveyed by chuting, the plant shall be of such size and design as to insure a practically continuous flow in the chute. The chutes shall be of metal or metal lined. The angle of the chute with the horizontal and the shape of the chute shall be such as to allow the concrete to slide without separation of the ingredients. The delivery end of the chute shall be as close as possible to the point of deposit. When the operation is intermittent, the chute shall discharge into a hopper. The chute shall be thoroughly flushed with water before and after each run: the water used for this purpose shall be discharged outside the forms. Chutes must be properly baffled or hooded at the discharging end to prevent separation of the aggregates.

1.14.4 PNEUMATIC PLACING (SHOTCRETING) (1993)

Shotcrete construction shall be in accordance with ACI Standard “Guide to Shotcrete” (ACI 506) and ACI Standard “Specification for Materials, Proportioning, and Application of Shotcrete” (ACI 506.2) of the ACI.

1.14.5 PUMPING CONCRETE (1993)

a. The pump and all appurtenances shall be so designed and arranged that the specified concrete can be transported and placed in the forms without segregation. The pump shall be capable of developing a working pressure of at least 300 psi and the pipeline and fittings shall be designed to withstand twice the working pressure.

b. Where it is necessary to lay the pipe on a down grade, a reducer shall be placed at the discharge end of the pipe to provide a choke and thus produce a continuous flow of concrete. When the type of pump is such that it discharges the concrete in small batches, or “belching,” a baffle box shall be provided into which the concrete shall be discharged. This box should preferably be of metal, about 2 feet square, with open sides so as to permit the concrete to flow into the forms at right angles to line of discharge. The pipe shall be not less than 6 inches nor more than 8 inches outside diameter, and the line shall be laid with as few bends as possible. When changes in direction are necessary they shall be made with bends of 45 degrees or less, unless greater bends are specifically permitted. If greater bends are permitted in special cases, they shall be long-radius bends. The maximum distance of delivery of concrete by pumping shall be 1000 feet horizontally and 100 feet vertically, unless otherwise specifically permitted by the Engineer. (A 90-degree bend is figured as equivalent to 40 feet of horizontal piping. A 45-degree bend is equivalent to 20 feet. A 22.5-degree bend is equivalent to 10 feet.) When pumping is completed, the concrete remaining in the pipeline if it is to be used, shall be ejected in such a manner that there will be no contamination of the concrete or separation of the ingredients. The pipeline and equipment must then be thoroughly cleaned. The pipeline can be cleaned by either water or air. If water is used, a pump shall be provided with a capacity of at least 80 gpm and capable of developing a pressure of 400 psi. Cleaning of the pipe can also be accomplished by the use of a “go-devil” which is propelled through the line by water or air pressure. (The “go-devil” is a dumbbell shaped piece with a rubber cup on each end. The cups are turned

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toward the liquid, or air, and the seal is the same as in a simple plunger pump.) If water is used, it must be discharged outside of the forms. On important work duplicate pumping equipment and additional pipe shall be provided to prevent delay due to breakdown of equipment.

1.14.6 COMPACTING (1993)

a. Concrete shall be thoroughly compacted during and immediately after depositing by vibrating the concrete internally by means of mechanical vibrating equipment, unless otherwise directed by the Engineer.

b. Internal mechanical vibrators shall be of a type approved by the Engineer. They shall be of sturdy construction, adequately powered, capable of transmitting vibration to the concrete in frequencies of not less than 3500 impulses per minute and shall produce a vibration of sufficient intensity to consolidate the concrete into place without a separation of the ingredients.

c. The vibratory elements shall be inserted into the concrete at the point of deposit and in the areas of freshly placed concrete. The time of vibration shall be of sufficient duration to accomplish thorough consolidation, complete embedment of the reinforcement, the production of smooth surfaces free from honeycomb and air bubbles, and to work the concrete into all angles and corners of the forms. However, over-vibration shall be avoided, and vibration shall continue in a spot only until the concrete has become uniformly plastic and shall not continue to the extent that pools of grout are formed. The length of time of vibration depends upon the frequency of the vibration (impulses per minute), size of vibrators and the slump of the concrete. This length of time must be determined in the field.

d. The internal vibrators shall be applied at points uniformly spaced, not farther apart than the radius over which the vibration is visibly effective, and shall be applied close enough to the forms effectively to vibrate the surface concrete. The vibration shall not be dissipated in lateral motion but shall be concentrated in vertical settlement in consolidation of the concrete.

e. The vibrator shall not be used to push or distribute the concrete laterally. The vibrating element shall be inserted in the concrete mass a sufficient depth to vibrate the bottom of each layer effectively, in as nearly a vertical position as practicable. It shall be withdrawn completely from the concrete before being advanced to the next point of application. f. To secure even and dense surfaces, free from aggregate pockets or honeycomb, vibration shall be supplemented by

working or spading by hand in the corners and angles of forms and along form surfaces while the concrete is plastic under the vibratory action.

g. A sufficient number of vibrators shall be employed so that, at the required rate of placement, thorough consolidation is secured throughout the entire volume of each layer of concrete. Extra vibrators shall be on hand for emergency use and for use when other vibrators are being serviced.

h. The use of surface vibrators to supplement internal vibration will be permitted when satisfactory surfaces cannot be obtained by the internal vibrations alone and when the contractor has obtained the approval of the Engineer of the equipment to be used. Surface vibrators shall be applied only long enough to embed the coarse aggregate and to bring enough mortar to the surface for satisfactory finishing.

i. The use of approved form vibrators will be permitted by the Engineer only when it is impossible to use internal vibrators. They shall be attached to or held on the forms in such a manner as to effectively transmit the vibration to the concrete and so that the principal path of motion of the vibration is in a horizontal plane.

1.14.7 TEMPERATURE (1993)

a. Concrete when deposited shall have temperatures within the limits shown in Table 8-1-13. b. The method of controlling the temperature of the concrete shall be approved by the Engineer.

1.14.8 CONTINUOUS DEPOSITING (1993)

Concrete shall be deposited continuously and as rapidly as practicable until the unit of operation approved by the Engineer is completed. Construction joints in addition to those provided on the plans will not be allowed unless authorized by the Engineer. If so authorized, they shall be made in accordance with Section 1.11, Concrete Jointing.

1.14.9 BONDING (1993)

Before new concrete is placed against hardened concrete, the surface of the hardened concrete shall be cleaned and all laitance removed. Immediately before new concrete is placed, the existing surfaces shall be thoroughly wetted and all standing water removed. Prior to placing fresh concrete, apply a bonding layer of mortar, usually 1/8 inch to 1/2 inch in thickness, which is spread on the moist and prepared hardened concrete surface. In lieu of mortar, a suitable commercial bonding agent may be used, when applied in accordance with manufacturer’s recommendations.

1.14.10 PLACING CYCLOPEAN CONCRETE (1993)

Cyclopean aggregate shall be thoroughly embedded in the concrete. The individual stones shall not be closer than 12 inches to any surface or adjacent stones. Stratified stone shall be laid on its natural bed. Cyclopean aggregate shall be carefully placed to avoid injury to forms or adjoining masonry.

1.14.11 PLACING RUBBLE CONCRETE (1993)

Rubble aggregate shall be thoroughly embedded in the concrete. The individual stones shall not be closer than 4 inches to any surface or adjacent stones. Rubble aggregate shall be carefully placed to avoid injury to forms or adjacent masonry.

1.14.12 PLACING CONCRETE CONTAINING SILICA FUME (2004)

1.14.12.1 Protection from Moisture Loss

Protection of concrete from early moisture loss is to begin at the first opportunity after placement and may require that such measures precede the curing phase of the work. Evaporation retarders, fogging and protection from the wind during the placement stage, or immediate curing, may be options included in the project specifications. Appropriate measures to protect against early moisture loss in concrete containing silica fume should be included and stressed in the project specifications. Subgrade moistening may be required to prevent excessive drying from the underside of the concrete.

1.14.12.2 Consolidation

Careful attention to effective vibration is required for concrete containing silica fume. Table 8-1-13. Concrete Temperature Limits

Temperature of Air Temperature of Concrete _{When Placed–Degrees F}

Degrees - F Minimum Maximum

Below 30 70 90

Between 30 and 45 60 90

Above 45 50 90

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1.14.13 PLACING CONCRETE CONTAINING FLY ASH (2004)

1.14.13.1 Air Entrainment

Tests shall be performed at the site to verify that the required amount of entrained air is present at the time of depositing the concrete.

1.14.14 WATER GAIN (1993)

Water gain is characterized by an accumulation of water at the surface. Whenever water gain appears in the concrete placed, the succeeding batches must be placed sufficiently dry to correct the over-wet condition by the reduction of the water cement ratio without changing the proportions of the other ingredients.

SECTION 1.15 DEPOSITING CONCRETE UNDER WATER