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Unformatted text preview: ach other shall be of same type and composition and shall be from the same cement works. 8.5 Cover Coating 8.5.1 The circumferential prestressing wires on the 9 ADDITIONAL CYLINDER PIPES core pipes shall be protected with a layer of rich cement mortar or concrete or any other approved material which prevents corrosion of wire. REQUIREMENTS FOR 9.1 The prestressed concrete cylinder pipes shall be manufactured to comply with the following additional requirements. 8.5.2 If cement mortar is used for cover coating, it shall be applied by rotary brushes or by other approved methods and shall preferably be applied within 16 hours after the prestressing wire is wound. The cement, sand and water shall be thoroughly mixed, before being fed into the cover coating machine. Minimum cement content in coating mortar shall be 540 kg/m3 and that for concrete 500 kglm3. Water cement ratio in the mix shall not be less than 0.27, if cement mortar is used for coating. Rebound or droppings not exceeding one fourth of the total mass of mix, may be used but the resulting mix proportions shall not be, leaner than original design mix. Rebound not used within one hour, shall be discarded. 9.1.1 Steel Socket and Spigot Rings Each ring shall be formed by one piece of steel or a number of pieces of steel butt-welded together. The rings shall be expanded beyond their elastic limit so that they are accurately shaped. The portion of the socket and spigot rings which shall be exposed afler the pipe is completed shall be smooth to prevent cutting of the rubber gasket during jointing and shall be protected from corrosion by a sprayed zinc coating of minimum thickness of 0.05 mm followed by one coat of bituminous paint. Other suitable protection maybe used with the approval of the purchaser. 6 IS 784:2001 9.1.2 Fabrication of Steel Cylinders sealing ring, the joint shall be self centreing, flexible and water tight. The joint shall be roll-on or confined type. Sockets of the pipes maybe projecting or flush with the barrel. Joint design shall be furnished by manufacturer before undertaking manufacture. The rubber ring joint design, shall take into consideration the tolerance for rubber chor~ tolerance for socket and spigot diameters, allowable deflection at joint and permanent set in the rubber ring. The cyiinder shall be accurately shaped to the size required and steel socket and spigot rings welded thereto after being jigged square with the longitudinal axis (except for bevel). Testing Before it is subjected to any further manufacturing process, each steel cylinder, with steel and spigot rings welded on, shall be subjected to water pressure which stresses the steel to at least 140 N/mm2, but not more than 175 N/mm2. While under stress, the assembly especially welds, shall be inspected and any parts showing leakage shall be repaired and the whole assembly retested. 11.2 The sealing rings shall be of such size that when jointed, in accordance with the manufacturer’s instructi...
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This document was uploaded on 10/01/2013.

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