- Concrete
The main factors for concrete used in PSC are:
• Ordinary portland cement-based concrete is used but strength usually greater
than 50 N/mm2;
• A high early strength is required to enable quicker application of prestress;
• A larger elastic modulus is needed to reduce the shortening of the member;
• A mix that reduces creep of the concrete to minimize losses of prestress;
You can see the importance creep has in PSC from this graph:
2.Steel
The steel used for prestressing has a nominal yield strength of between 1550 to
1800
N/mm2. The different forms the steel may take are:
• Wires: individually drawn wires of 7 mm diameter;
• Strands: a collection of wires (usually 7) wound together and thus having a
diameter that is different to its area;
• Tendon: A collection of strands encased in a duct – only used in posttensioning;
• Bar: a specially formed bar of high strength steel of greater than 20 mm
diameter.
Prestressed concrete bridge beams typically use 15.7 mm diameter (but with an
area
of 150 mm2)7-wire super strand which has a breaking load of 265 kN.
