requirements of prestressed concrete; Image Courtsey: Archi Expo
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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 Concrete
The basic requirements of prestressed concrete are:
High Strength Capacity
Low Shrinkage
Low Creep
High Durability
Properties of various materials used in prestressed concrete must suit the requirements which are connected with the performance of prestressed concrete.
1. Strength Requirements of Prestressed Concrete
Prestressed 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
When compared to conventional concrete, prestressed concrete is subjected to higher compressive stress, hence the concrete demands high strength.
The use of high strength concrete helps in achieving following prestressed concrete requirements:
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
The 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 Concrete
The 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 Concrete
The 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:
