Of ingredients is carried out at the nozzle or gun

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Unformatted text preview: ent of the minimum ul’timatetensile strength of wire, when counter-weight or break system is used for developing tension. If tension is developed by use of a die, then the initial stress in the wire shall not exceed 65 percent of the ultimate tensile strength of wire. 8.5.4 The compressive strength of the cover coating mortar shall be obtained from cubes having area of face 50 cmz or the compressive strength of the cover coating concrete shall be obtained from cube having area of face 100 cm2 and shall not be less than 35 N/mmz at the time of factory testing of pipe. 8.4.3 The initial compressive stress induced in the core concrete shall not exceed 55 percent of the compressive strength of the concrete in the pipe at the time of tmnsfkr. 8.4.4 Methods and equipments for wrapping the wire shall be such that wire shall be wound around the core in a helical form at the predetermined design spacing and capable of controlling the tension. Wire splicing shall be capable of withstanding a force equal to the full strength of wire. At the ends of core pipe, the wire shall continue for at least one extra circumferential turn before being anchored. 8.5.5 The mortar coating shall have a minimum cover of 18 mm and concrete coating shall have a minimum cover of 25 mm, over all steel, except at end face and the spigot portion going inside socket, where it will be not less than 15 mm. To achieve adequate bond between core and coat, approved bonding agent shall be applied, at ends of pipe for a width of 100 mm, along the circumference to prevent separation between core and coat, at ends. 8.4.5 The clear spacing between the successive turns of the circumferential prestressing wires shall be not less than 6 mm, except at ends or at joints and shall be not more than 50 mm. Concurrently with the mortar coating, a cement slurry shall be applied on to the core at a rate of not less than 0.5 l/m2 just ahead of the mortar coating. The slurry shall consist of 1.2 kg of cement to per Iitre of water. 8.4.6 Test Cube Conversion Factors 8.5.6 The thickness shall be checked for every pipe as soon as, coating is done. The core concrete compressive strength shall be taken on 150 mm x 150 mm cubes. Where the process of manufacture is such that the strength of concrete in the pipe differs from that given by tests on vibrated cubes, the two may be related by suitable conversion factors. If the purchaser requires evidence of these factors, he shall ask for it, before placing the order. The core concrete strength shall be obtained by multiplying the cube strength with the conversion factor and shall be used for design purpose. 8.5.7 Mortar Soundness After the mortar coating is cured and prior to transport, the coating on each pipe shall be checked for delamination and hollows by tapping the exterior with a hammer having a head mass of not more than 0.5 kg. Any hollows or drumming areas detected by sounding shall be repaired by approved methods. 8.5.8 All cement coming in contact with e...
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