Prestressed concrete is used in a wide range of building and civil structures where its improved performance can allow for longer spans, reduced structural thickness, and materials saving compared with simple RCC. Prestressed concrete is also a special type of concrete. As we are aware of the fact that concrete is good in compression and weak in tension. We stress the concrete in the production stage itself by compressing the concrete so as to enhance the tensile properties of concrete.
Materials commonly used for prestressed concrete are :
- High Strength concrete – Minimum grade of concrete which we can use for prestressed concrete is M40 and M30 for post-tensioned concrete. Maximum cement content should not be more than 530 kg/cu.m.
- High strength steel – Use high-strength steel wires, cables, or bars. Generally, the diameter of the steel wires is 2 to 5 mm diameter. In the case of bars, the diameter can vary from 10 mm to 32 mm.
Necessity of using High strength steel and concrete
The working stress of mild steel is 140 N/mm2, which is lost completely due to elastic deformation, creep, and shrinkage of concrete.
High strength concrete is necessary for prestressed concrete because of the following reasons :
- The material offers high resistance in tension shear, bond, and bearing.
- In the zone of anchorages, the bearing stress being higher, prefere high strength concrete to minimize costs.
- High-strength concrete is less liable to shrinkage cracks.
- It has a higher modulus of elasticity and smaller ultimate creep strain resulting in a smaller loss of prestress in steel.
- The use of high-strength concrete reduces the cross-sectional dimensions.
- With less cross-section, a larger span is possible and becomes technically and economically practical.
Different methods of Prestressing
- Pretensioning system – For small spans and mass production is possible.
- Post-tensioning system – For longer spans bridges.
Check this post to know more about prestressed concrete.
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