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discharged outside of forms. 10.3.3 PUMPING Where concrete is conveyed and placed 6y mechanically or pneumatically applied pressure, the equipment shall be suitable in kind and adequate in capacity for the work. The operation of the pump shall be such that a continuous stream of concrete without air pockets is produced. Slump loss in the concrete should not exceed 1.5 inches from the pump hopper to the point of placement. When pumping is completed, the concrete remaining in the pipeline shall be ejected in such a manner that there will be no contamination of the concrete in place. After this operation the entire equipment shall be thoroughly cleaned. 10.3.4 OTHER PLACEMENT METHODS Placement methods using buckets, conveyors, drop chutes, elephant trunks, tremies, and portholes should follow the guidelines set forth in ACI 304R and ACI 350. 10.4 PLACEMENT OF LAYERS Concrete layers shall be deposited in horizontal layers 12-24 inches deep. Each layer shall be thoroughly consolidated before the succeeding layer is placed. Timing of placement shall be such that each succeeding layer is placed before the preceding layer has reached its initial set. 10.5 CONSOLIDATION 10.5.1 During and immediately after placing, all concrete shall be consolidated and worked to provide thorough placement around all reinforcement, embedded fixtures, and into corners of forms. Unless otherwise approved by the Engineer, the Contractor shall accomplish consolidation by the use of high-frequency internal vibrators with a minimum frequency of 8000 revolutions per minute. The type and operation of vibrators is subject to the Engineer's accep- tance. Concrete should be vibrated in accordance with the recommendations contained in ACI 309R. 10.5.2 EXTENT OF VIBRATION Vibration shall extend through the entire depth of each new layer and several inches into the preceding layer, at no time penetrating more than 2 . ft. into the underlying layer. Vibration shall be applied at the point of deposit and uni- formly throughout the freshly placed concrete. 10.5.3 DURATION OF VIBRATION Usually vibration should secure the desired results within five (51 to fifteen (15) seconds at points eighteen inches SPEC B -CONCRETE PAGE 15