Strength and durability are the basic requirements of prestressed concrete. The prestressing levels are determined such a way that the structural member show desired performance safely and economically.
Main requirements of prestressed concrete are explained in the below section.
Requirements of Prestressed ConcreteThe basic requirements of prestressed concrete are:
- High Strength Capacity
- Low Shrinkage
- Low Creep
- High Durability
1. Strength Requirements of Prestressed ConcretePrestressed Concrete is required to show high compressive, tensile and shear strength from an early age itself. In order to achieve this, the prestressed concrete must gain strength at an early stage in a higher amount. Achieving higher strength at an early age will make the prestressed concrete construction faster. This helps to start the pre-tensioning process early. High-strength prestressed concrete can be achieved by the use of:
- High-Strength Concrete Mix
- Admixtures and Superplasticisers
- Pozzolans like fly ash and silica
- A higher value of Young's modulus
- Greater Density Concrete
- Quality control during production
- High modulus of elasticity
- Fewer chances of shrinkage cracks
- Smaller loss of prestress in tendons
- The ultimate creep value is less
- High strength is obtained from small cross-sectional dimensions
- Lightweight prestressed concrete sections are obtained
2. Low Shrinkage Values for Prestressed ConcreteThe early shrinkage value of prestressed concrete is required to be less. A low shrinkage value can be obtained by having a rich and controlled mix. If the shrinkage is not controlled, the prestress in tendons will be lost as time passes. The prestressed concrete is adequately cured and load application is delayed in order to reduce the shrinkage issues. This will hence increase the durability of prestressed concrete.
3. Creep Value for Prestressed ConcreteThe prestressed concrete must be properly cured and the load application must be delayed to reduce the creep. To check this, the creep values are monitored as creep strain versus time. Durability, deflection and prestress loss can be reduced by preventing creep in prestressed concrete.
4. Durability of Prestressed ConcreteThe durability requirement of prestressed concrete is achieved by bringing quality prestressed concrete construction. The resistance of the prestressed concrete against deterioration and the environmental conditions will judge the durability. Higher the quality of the concrete, high is its resistance to chemical attacks, frost action, and fire exposures. A durable prestressed concrete can be obtained by:
- The use of high strength concrete
- Quality construction
- Use of the correct water-cement ratio
- Proper Compaction of Concrete
- Make the concrete dense and impermeable
- Make cement rich mix
- Reduce early shrinkage and creep issues