At the central plant shall be done in accordance with

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Unformatted text preview: pe, so constructed that all materials in the concrete are kept uniformly distributed throughout the mass. The mixer At the proportioning plant, all solid shall be water-tight when closed. materials shall be accurately weighed and charged into the drum; the prescribed quantity of water may either be charged iuto the drum or measured and placed in the tank meant for carrying the mixing writer. Trudr mixers shall be provided with some device whereby the time of hauling, mixing, and introduction of water could be readily checked. ‘4.7.4 Hand Mixing - Hand mixing slrould Hand mixing, if authorized crete construction. work, shall be done on a water-tight platform. turned over using shovels as many times as may homogeneous concrete of uniform consistency. be avoided in mass confor minor portions of the The entire mass shall be be necessary to produce 4.7.5 Retemperiq - The retempcring of partially hardened concrete or mortar requiring renewed mixing, twith or without the addition of cement, aggregate or water, shall not be permitted. 4.8 Handling and Conveying 4.8.1 The handling and convc,ying of concrete from the mixer to the and without place of final deposit shall be dorlc> as rapidly as practicable any objectionable separation or 14~5 of ingredients. Whenever the length of haul from the mixing plant to the place of deposit is such that the concrete unduly compacts or segregates, suitable agitators shall be installed in the conveying system. Where concrete is being conveyed on chutes or on belts, the free fall or drop shall be limited to 5 ft ( or 150 cm ) unless otherwise permitted. The concrete shall be placed in position within 30 minutes of its removal from tlic mixer 14 is : 457 - 1957 4.8.2 Handliwg Equibmeut 4.8.2.1 Buckets - 13uckets if used, shall be of the bottom-dump type, permitting an even, controlled flow into the forms or hopper without undue splashing or segregation. Cars, trucks and skips shall be designed to facilitate uniform delivery rather than quick dumping. 4.8.2.2 Chutes - Where concrete is conveyed in chutes, the trough of the chutes shall be of such size and shape as to ensure a steady, uniform flow of material. The sections shall be made of, .or lined with metal and al! runs shall have approximately.the same slope, not flatter than 1 vertical to 2) horizontal. The layout shall be such that the concrete will slide evenly in a compact mass without any’separation or loss of ingredients. The required consistency of the concrete.shall not be changed in order to facilitate chuting. Where it becomes necessary to change the consistency, the concrete mix shall be completely re-designed. Wherever there is a free fall within the conveying system, suitable baffle plates, splash boards or down spouts shall be provided to prevent segregation, splashing, or loss of ingredients. Wherever it is necessary to hold the discharge end of a chute more than 300 cm ( or 10 ft ) above the level of the fresh concrete, a flexible down spout shall b...
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