Prestressed Concrete Pipes (Including Fittings)
2001 Edition

IS 784 permits several types of cement for producing prestressed concrete pipes, including 43 grade Ordinary Portland Cement (IS 8112), 53 grade Ordinary Portland Cement (IS 12269), Rapid Hardening Portland Cement (IS 8041), and Portland Slag Cement (IS 455) with slag content up to 50%. Additionally, Sulphate Resisting Portland Cement (IS 12330) is specified for environments with significant sulphate presence. The cement used in contact must be uniform in type and sourced from the same manufacturing unit to ensure consistent properties and durability under service conditions.

According to IS 784, tolerances for pipe length and internal diameter depend on the pipe's size and length. For pipes shorter than 4 meters, diameter tolerances are ±5 mm for diameters up to 350 mm and ±10 mm for larger diameters. For pipes 4 meters or longer, internal diameter tolerances differ between measurements near the pipe ends and the middle section; for example, pipes up to 900 mm diameter have ±6 mm tolerance within 600 mm of the ends and ±9 mm elsewhere. Measurements are taken at both ends (50 mm from ends) and at the center for pipes over 700 mm in diameter, using Go/No Go gauges to ensure compliance.

Prestressing wires must adhere to standards such as IS 1785 (Part 1 & 2), IS 6003, or IS 6006. For longitudinal wires, the tensile strength may be reduced by up to 15% from the ultimate tensile strength to prevent damage during wire threading or anchoring. Circumferential winding tension is controlled with maximum initial stresses at 75% of minimum ultimate tensile strength when employing a counter-weight or break system, and 65% if tension is developed through the die process. The tension is maintained positively until detensioning to ensure structural integrity, with allowable stresses accounting for prestress losses.

IS 784 requires several tests to confirm pipe quality, including a design proving test conducted on 4-5 pipes of a new diameter at the highest pressure rating without external loading. Factory hydrostatic tests per IS 3597 must be performed to check for leaks, with pipes allowed wet patches but no seepage. The permeability of coatings is assessed by measuring water absorption, with limits set for initial and final absorption volumes. Pipes failing tests are either repaired and retested or rejected. Non-pressure pipes undergo permeability, dimensional, and three edge bearing tests, with sampling and acceptance criteria based on lot sizes.

IS 784 specifies that mortar coating over steel reinforcement must have a minimum thickness of 18 mm, except at pipe ends or spigots where 15 mm is allowed. Concrete coatings should be at least 25 mm thick, with the same exception for ends. Before applying mortar, a cement slurry with a minimum concentration of 1.2 kg cement per liter of water is applied to ensure good bonding. Mortar should be applied preferably within 16 hours after winding prestressing wires, with mix proportions ensuring adequate strength and water-cement ratios. Curing is performed separately for the concrete core and the coating, using water, steam, or approved compounds, with durations to achieve specified strength levels.