2. Concrete: Prestress concrete requires concrete, which has a high compressive
strength reasonably early age with comparatively higher tensile strength than
ordinary concrete. The concrete for the members shall be air-entrained concrete
composed of Portland cement, fine and coarse aggregates, admixtures and water.
The air-entraining feature may be obtained by the use of either air-entraining
Portland cement or an approved air-entraining admixture. The entrained air
content shall be not less than 4 percent or more than 6 percent.
Minimum cement content of 300 to 360 kg/m3 is prescribed for the durability
The water content should be as low as possible.
3. Steel:- High tensile steel , tendons , strands or cables
The steel used in prestress shall be any one of the following:(a) Plain hard-drawn steel wire conforming to IS1785 (Part-I & Part-III)
(b) Cold drawn indented wire conforming to IS6003
(c) High tensile steel wire bar conforming to IS2090
(d) Uncoated stress relived strand conforming to IS6006
High strength steel contains:
0.7 to 0.8% carbons,
Durability, Fire Resistance & Cover Requirements For P.S.C Members:According to IS: 1343-1980
20 mm cover for pretensioned members
30 mm or size of the cable which ever is bigger for post tensioned members.
If the prestress members are exposed to an aggressive environment, these covers are
increased by another 10 mm.
Necessity of high grade of concrete & steel:
Higher the grade of concrete higher the bond strength which is vital in pretensioned
concrete, Also higher bearing strength which is vital in post-tensioned concrete. Further
creep & shrinkage losses are minimum with high-grade concrete.
Generally minimum M30 grade concrete is used for post-tensioned & M40 grade
concrete is used for pretensioned members.