Small diameter precast concrete pipes are normally manufactured by spinning method. The spinning method basically makes use of the principle of centrifugal forces which diminishes towards the centre of precast pipe. Hence, problems like the presence of voids and variation of dimension occur frequently and remedial works like filling of voids by cement mortar has to be carried out depending on the severity of deficiency.
Large diameter precast concrete pipes are commonly produced by vertical casting method. In this method the concrete pipes are normally placed upright with spigot staying on top, resting on socket moulds before the freshly-placed concrete has set. There is a possibility of deformation of pipe spigots to form oval shapes.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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