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Splash boards or down spouts shall be provided to

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Unformatted text preview: e used to break the fall and confine the flow. The lower end of the spout shall be held close to the place of deposit. Wherever depositing is intermittent, a discharge hopper shall be provided. All chutes shall be thoroughly cleaned before and after each run. All wash water and debris shall,be wasted outside the forms. Pumping - ‘Zhere concrete is permitted to be conveyed into place by the application of pressure, the pump and piping shall be suitabty designed and shall be of adequate capacity ior the work. Pumping shall be permitted only for conveying concrete containing aggregates less than 7.5 cm ( or 3 in ) maximum size. The operation of the pumping system shall be such that a continuous streAm of concrete, without air pockets or interruptions, is delivered. At the end of the run, all concrete remaining in the pipe line shall be rejected in such a manner as to avoid any segregation or lack of uniformity. The pump and line shall be thoroughly cleaned and al! *:;ash water and debris wasted. Belt conveyors -Where transportation by means of belt conveyors is permitted, a steady, uniform flow of concrete shall be maintained without any segregation or piling up on steep inclines or at transfer points. The conveyor shall be covered to prevent damage by rain, loss of heat during cold weather, evaporation or heating by the direct rays of the sun,,or’other deterioration of the concrete. Concrete shall not be discharged directly into the forms, unless the discharge end of the conveyor or pipe can be readily moved about within the forms so as to place the concrete in even layers as specified under 4.10.2, 15 IS i 457 - 1957 and 4.10.10. Otherwise, suitable hoppers shall be provided, from which the concrete shall be dumped in place by means of buckets and short chutes or spouts. 4.8.3 Cleaning Epipment - At the end of each run and before again placing any concrete, all hardened concrete or mortar shall be removed from the inner surface of the conveying equipment. All conveying equipment shall be maintained in good order and kept reasonably free from deposits of stiff concrete and leakage of mortar. 4.9 Preparation for Placing Concrete 4.9.1 Before depositing any concrete for the ;lexC lift or pour, the forms Shall not be retightened. The surface of contact shall be allowed ’ to dry out between placing successive lifts of concrete. The top of the previously deposited concrete shall be thoroughly cleaned and prepared as specified under 4.10.5. Where new concrete is to be bonded to hard concrete, unless otherwise ordered and in addition to the requirements specified under 4.105,. the vertical and inclined surfaces which cannot be covered with mortar shall be given a heavy coat of neat cement grout, vigorously brushed into all interstices and hollows so as to provide the best possible conditions for bond and impermeability. 4.9.2 Rock Foundations -- All rock surfaces against which concrete is to be placed shall be clean and free fr...
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