Be cured for a minimum period of 7 days if water

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Unformatted text preview: ays. 8 MANUFACTURE 8.1 Core 8.1.1 Moulds The moulds and method of manufacture of pipe shall be such that the form and dimensions of the finished pipe conform to the requirements given in 5 and 12 and the surface and edges are clean and true. 8.3 Pretensioning Wires and Release of Longitudinal The concrete core shall be longitudinally prestressed, including the socket, by means of high tensile steel wires or strands, which shall be provided with permanent anchorages embedded in the concrete, within the joint portion at each end. The centreline spacing between the longitudinal wires measured along the barrel shall not exceed twice the core thickness or 150 mm, whichever is greater, subject to the provision of 7.4.1(c). 8,1.2 Concrete Mix The proportions of cement, fine aggregate, coarse aggregate and water used in concrete for pipe core shall be determined and controlled as the work proceeds to obtain homogeneous,dense, workable, durable concrete of specified strength in the pipe, and minimum defects on the surface of the pipe. The proportions shall be those, that will give the best overall results with the particular materials and the methods of placing used for the work. A minimum of 350 kg/m3 of cement shall be used for concrete. The water cement ratio shall be such, as to ensure that the concrete will meet the strength requirements, but in no case it shall exceed 0.5. The soluble chloride ion content of the concrete or mortar mix, expressed as a percentage of the mass of cement shall not exceed 0.20 percent. The clear cover of concrete overall steel reinforcement including the ends of the longitudinal prestressing wires, shall be such that in any finished pipe it is nowhere less than 12 mm. 8.3.1 The longitudinal wires shall be stressed to the designed tension, taking into account the loss of stress in wire. The tension shall be maintained by positive means till detensioning. 8.3.2 The tensioned wires shall not be released until the concrete in the core has attained a compressive strength of at least two times the initial longitudinal prestress or 15 N/mm2 whichever is greater. Unless the design calls for higher concrete strength, the minimum compressive strength of concrite shall not be less than 40 N/mmz at 28 days. 8.1.3 Placing of Concrete 8.4 Circumferential The concrete in the cores maybe placed either by the centrifugal method, vertical casting method, or by other approved methods. For centrifugal spinning method, concrete shall be deposited in the mould and the speed of rotation during placing shall be such, Prestressing 8.4.1 Circumferential prestressing shall not take place until the concrete in the core has reached a minimum compressive strength of 25 N/mm2, or as per the design requirements whichever is greater. 5 IS 784:2001 8.5.3 Pneumatic process in which mixing of ingredients is carried out at the nozzle or gun, shall not be permitted. 8.4.2 The initial stress in the wire during circumferential winding shall not bemorethan 75 perc...
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