External Post Tensioning – Wissington Sugar Factory Silo Repair

External Post Tensioning – Wissington Sugar Factory Silo Repair, Norfolk

British Sugar

Principal Contractor
Amey Inter Urban

Works Commenced
July 2015

Works Completed
November 2015


Wissington Sugar Factory in Norfolk is the largest sugar beet factory in the world. The factory’s silo two was constructed in the 1970s and is 50 metres tall and around 20 metres in diameter.

A site inspection identified three separate locations where the concrete had spalled and the pre-stressing tendons had become exposed and corroded.

Freyssinet was commissioned to provide a post-tensioning design to substitute the tendon forces lost due to corrosion of existing tendons. The basis of Freyssinet’s PT design was to provide the compressive force that is similar to the existing force in the tank wall around the affected area.

Freyssinet’s design approach was to use external post tensioning using the Freyssinet 1X15 system. The tendons were installed near to the existing corroded tendons, with the final positions of the new external tendons chosen to provide minimum increase in concrete residual stress. The Freyssinet 1X15 system is an un-bonded PT that was installed into two semi circles to form a loop.

As part of the works, Freyssinet also carried out concrete and roof repairs and waterproofing. The project was completed on October 2015.

Freyssinet subsequently won the Phase 3 contract to install post-tensioning tendons and X anchors to silo 5 at the sugar factory. These works were completed in October 2016.