Specification for Monostrand Unbonded Tendons
     (PTI Specs., ACI 423.6-01, IS 14268:1995)

Prestressing Steel

• Low-Relaxation 7 wire Strand of Class II (Grade 270) with 12.7 mm nominal diameter used in Monostrand Unbonded post tensioning tendons shall conform to the requirements of ASTM A 416/A 416M
• Sectional steel area of Strand: 98.7 mm2
• Yield Load: Not less than 180 kN
• Ultimate Strength: Not less than 1860 N/mm2
• Minimum Breaking Strength: Not less than 183.7 kN
• Modulus of Elasticity: At least 196,500 N/mm2
• Minimum elongation: 3.5% for gage length of 600 mm
• Relaxation at 1000 hours: Less than 2.5% @ 70% Minimum Ultimate Tensile Strength
• Weight of Strand: More than 0.775 kg/m
• Sheathing Specifications:
• Sheathing material: polyethylene or polypropylene
• Minimum Density: 0.941 gram/cm3
• Inside Diameter: At least 0.76 mm greater than the maximum diameter of the strand
• Appearance: Sheathing shall provide a smooth circular outside surface and shall not visibly reveal lay of the strand
• Coverage: Sheathing shall be continuous over the entire length to be un-bonded & shall prevent intrusion of cement paste or loss of PT coating
• Grease Coating Specifications:
• Grease coating shall provide protection against corrosion to the Prestressing steel
• It shall provide proper lubrication between the strand & sheathing
• It should resist flow within anticipated temperature range of exposure
• It should provide continuous non-brittle coating at lowest anticipated temperature of exposure
• It should be chemically stable & non-reactive with Pre-stressing steel, reinforcing steel, sheathing material & concrete
• It shall be a compound with appropriate moisture displacing & corrosion-inhibiting properties
• Minimum weight of the grease coating on the Pre-stressing strand shall not be less than 1.14 kg per 30.5 m (37.4 grams/m) for 12.7 mm diameter strand

Anchorage

• Mono-strand anchorages of un-bonded tendons shall be designed to develop at least 95% of the actual strength of Prestressing steel with following Mechanical Properties:
• Material: SG Iron
• Hardness: 170 to 230 BHN
• Bearing Area: 7239 mm2