ACI 304R PDF
ACI R Guide for Measuring, Mixing, Transporting, And Placing Concrete – Download as PDF File .pdf), Text File .txt) or read online. werewrerrr. ACI R: Guide for Measuring, Mixing, Transporting, and Placing Concrete. Buy ACI R (R) Guide For Measuring, Mixing, Transporting And Placing Concrete from SAI Global.
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Form faces should be treated with a releasing agent to prevent concrete from sticking to the forms and thereby aid in stripping. Persistent requests for the addition of water should 304rr investigated.
With either placement method, the loss of seal likely will result in washing and segregation. When a screeded or troweled finish is required, the grout should be brought up to flood the aggregate surface and any diluted surface grout should be removed by brooming. Pay particular attention to the storage of special concrete aggregates, including lightweight, high-density, and architectural-finish aggregates.
In underwater construction, higher placing rates at lower cost have been achieved by this method than by conventional placement methods.
This type of batching system provides greater accuracy for high-speed production than either the manual or semiautomatic systems. When specification limits for grading cannot be met consistently, special handling methods should be instituted. Silos should be equipped with nonclogging air-diffuser flow pads through which small quantities ac dry, oil-free, low-pressure air can be introduced intermittently at approximately 3 to 5 psi 20 to 35 kPa to loosen cement that has settled tightly in the silos.
Where practical, it is advantageous to have radio or telephone communications between the site of major placements and the batching and mixing plant to better control delivery schedules and prevent excessive delays and waste of concrete.
Bureau of ReclamationCorps of Engineers a. Bureau of Reclamation ; Tynes Form coatings that are satisfactory on wood are not always suitable for steel forms; for example, steel forms would require a coating that acts primarily as a releasing agent, whereas plywood afi a coating that also seals the forms against moisture penetration.
Use only as much water and fine aggregate as is required to achieve ack workability for proper wci and consolidation by means of vibration.
The ACI R recommends the application of baffle and drop at the end adi the chute aci r 304rr concrete separation and make sure that concrete stay on the aci r. When the horizontal surface procedure is not practical, as when plan dimensions are relatively large compared to the depth, the advancing slope method is used. Once the appropriate time in the sequence is determined, chemical admixtures should be charged to the mixer at acj same point in the mixing sequence for every batch.
In difficult and obstructed acj, supplemental form vibration can be used. The selection of handling equipment should be based on its capability to efficiently handle concrete of proportions most advantageous for being readily consolidated in place with vibrators. Presetting of desired batch weights is completed by such devices as punched cards, digital switches, or rotating dials and computers.
If liquid admixtures are frozen, they should be properly reblended before they are used in concrete.
The interior of a cement silo should be smooth, with a minimum bottom slope of 50 degrees from the horizontal for a circular silo and 55 to 60 degrees for a rectangular silo. The pipe is normally lowered to bottom contact, then gradually filled.
Free Fall Of Concrete | ASCC Position Statements
Effective control of segregation and undersized materials is most easily accomplished when the afi of maximum-to-minimum size in each fraction is held to not more than four for aggregates smaller than 1 in. The admixture dosage is typically selected to wear off shortly after the concrete arrives at the placement site, allowing the concrete to set normally. AEA effectiveness and the resulting dosage of AEA also depend on the cement fineness, cement factor, and water content, and the chemistry of cement and water, as well as that of other chemical and mineral admixtures used in the concrete.
As the range of sizes in each fraction is decreased and the number of size separations is increased, segregation is further reduced.
ACI 304R-89 – Guide for Measuring, Mixing, Transporting, And
Concrete placed under water has also been used to add weight to sink precast tunnel sections, to join tunnel sections once in place, and to repair erosion or cavitation damage to major hydraulic structures Gerwick ; Gerwick, Holland, and Kommendant If free water does accumulate, however, it should be removed by blotting with mats, draining, or pulling off with a loop of hose so 304t the surface loses its water sheen before the next finishing operation is performed. If that mixture has a curve running in a zigzag fashion, or has one or more values falling below the boundary line, the mixture is questionable for pumping and may not be pumpable by all types of concrete pumps.
Satisfactorily designed mixers have a blade or fin arrangement and drum shape that ensure an end-to-end exchange of materials parallel to the axis of rotation or a rolling, folding, and ai movement of the batch over itself as it is being mixed.
There is no evidence that other structural properties differ from those of similar concretes placed in the dry.
When air entrainment is required to a higher extent than that provided by the gas-forming fluidifier, air-entraining agent should be added separately. Mixture and batch-size selectors, aggregate moisture meters, manually controlled fine aggregate moisture compensators, and graphic or digital devices for recording the batch weight of each material are required for good plant control Van Alstine ; Lovern Explore the Home Gift Guide.
Any normalweight or lightweight acii concrete that can be discharged by a truck mixer can be 30r by a concrete belt conveyor. Because heating either water or aggregates can cause erratic slump-loss behavior, extreme care should be taken when such procedures are used to raise the concrete temperature.
R Guide for Measuring, Mixing, Transporting, and Placing Concrete (Reapproved )
Dirt and debris should be prevented from filtering down to the grout surface. Ensure that the batched materials are properly sequenced and blended so that they are charged uniformly into the mixture U. The discharge of powered placement booms can be ai at almost any point within the radius of the boom and at elevations achieved with the boom from near vertical up or down to horizontal.
Because the success of an underwater placement depends largely on the concrete itself, sampling and testing during the placement are critical to ensure compliance with approved mixtures and required concrete characteristics slump, air content, temperature. These conditions can dictate the type of transportation best acu for economically obtaining quality in-place concrete.
Maximum volume output and maximum pressure on the concrete cannot be achieved simultaneously from most concrete pumps because this combination requires too much power.