Prestressing strand is supplied to site in ducts of large diameter in such a way that they are protected against damage or corrosionز

But still i ask you how much the size????

The cross sectional area of duct is normally 2.5 times that of the area of prestressing steel. The size of ducts should not  be too small because of the followings:

(i) Potential blockage by grout

(ii) Excessive development of friction

(iii) Difficulty in threading prestressing tendon

Good information DEbasish. 2.5 times diameter is like the ratio of electrical conduits.

Regards.

Dr Debasish Mondal, Can you inform me in which code, these criteria is suggested??

See we are one of the leading engineering consultant in India, this is what we follow. Indian standards also recommends this.

Dear Debasish, can you send a copy from this item regarding cable size for prestressing tendons?

Dear Dr. Abbas

Please see 12.1.2.3

THank you Dr Mohannad