Metallic sheath for posttensioning method

In a prestressed concrete structure executed by posttensioning method, a metallic sheath having an inner peripheral surface thereof in sliding contact with a tendon coated with a solid lubricating coating including polytetrafluoroethylene (PTFE). By the use of this metallic sheath, the sliding frictional resistance produced between the metallic sheath and tendon when the tendon is subjected to tensioning operation is considerably decreased to increase the prestressing force introduced into the structure accordingly. The solid lubricating coating is excellent in flexibility and contact properties, and good characteristics of coating are imparted to the sheath.