How does a bonded post-tensioning system work?

A bonded post-tensioning system is a method of reinforcing concrete by tensioning steel tendons after the concrete has hardened, with the tendons being permanently bonded to the concrete

Components

Tendons: High-strength steel cables or bars

Ducts: Plastic or metal tubes that house the tendons

Anchorages: Devices at the ends that transfer tension to the concrete

Grout: Cementitious material that fills the ducts

Working Process

1 Installation Phase

Ducts are placed in the concrete formwork according to the structural design

Tendons are inserted into these ducts before concrete is poured

Anchorages are positioned at both ends of the tendons

2 Concrete Pouring and Curing

Concrete is poured around the ducts and tendons

The concrete is allowed to cure to sufficient strength (typically 70-80% of design strength)

3 Tensioning Process

Hydraulic jacks apply tension to the tendons

Tendons are stretched to the specified force (usually 70-80% of their ultimate strength)

The tension is maintained while anchorages are secured

4 Bonding Phase

Grout is pumped into the ducts under pressure

The grout fills all voids between the tendon and duct

Once cured, the grout creates a permanent bond between tendon, duct, and concrete

Key Advantages

Increased structural capacity: Allows for longer spans and thinner sections

Crack control: Reduces or eliminates cracking under service loads

Durability: The bond protects tendons from corrosion

Load redistribution: Stresses are more evenly distributed throughout the structure

Applications

Bridges and parking structures

High-rise buildings

Industrial facilities

Slabs and beams with large spans