Patent ID: 7861507

Claim:
A high-strength prestressing strand having a seven-wire structure in which one core wire and six outer wires are stranded, wherein an external diameter of the strand is from 15.0 mm to 16.1 mm, a total cross-sectional area of the strand is 135 mm 2 or more, a load at 0.2% permanent elongation is 266 kN or more, wherein a relaxation value measured after a 1000-hour relaxation test is 2.5% or lower, wherein a diameter of the core wire is 5.35Â±0.3 mm and a diameter of the outer wires is 5.15Â±0.25 mm, wherein the core wire and the outer wires each comprise a carbon concentration of 0.90% or more, and wherein the prestressing strand is manufactured by: stranding the core wire and outer wires; giving a stretching treatment; and giving a bluing treatment at a temperature of 380Â° C. or more and 430Â° C. or less after or at the same time with the stretching treatment.