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Harrow Bridge 

Description Works
FM Conway has been working with Westminster City Council to deliver a high-quality asset maintenance project on elements of the super-structure forming parts of the elevated Harrow Road Viaduct. Constructed in the 1960s as part of the A40 Westway, the elevated Harrow Road highlighted several areas of the structure that were subject to deterioration, together with other durability concerns. 

Services used on this project Structures Traffic Management
Delivering Innovation

The work had to be carried out in a series of stages over a nine month period, supplying a new cathodic protection system within the columns, crossheads and soffits of the bridge to prevent corrosion and maintain structural integrity. To access the current system, FM Conway used a hydro-demolition technique on 18 individual pillars of the bridge, removing 15mm of the existing structure. Due to the nature of the works, FM Conway designed a bespoke fully incapsulated scaffold for the safety of operatives and members of the public. 

Once exposed, FM Conway was able to investigate and address failing elements within the cathodic protection system that had reached their end of life.  The cathodic protection technique mitigates the corrosion of the structure by making the surface the cathode of an electrochemical cell.  By applying controlled amounts of electrical current to the metal, restricted levels of corrosion within the structure could be achieved, which maximises durability. FM Conway then sprayed concrete over the cabling of the cathodic protection system for 25mm, which was able to effectively cure after a seven day period. 

Louisa Augustine-Fraser, Bridge Engineer at Westminster City Council, explained:
"The complexity of this scheme combined with its location highlights FM Conway’s ability to deliver excellence within high-profile, challenging environments. The Project Managers displayed outstanding communication skills and ensured the team had a proactive approach throughout, maintaining close collaboration to address emerging challenges and successfully complete the scope of works."

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The complexity of this scheme combined with its location highlights FM Conway’s ability to deliver excellence within high profile, challenging environments.

Louisa Augustine-Fraser - Bridge Engineer at Westminster City Council
Challenges and Solutions

The elevated Harrow Road, which belongs to Westminster City Council, exists beneath the A40 Westway, which is owned and maintained by Transport for London. In addition to that, the ground level is a privately-owned local access road, so the challenge for the team was to manage and meet the expectations of all stakeholders, whilst minimising disruption and ensuring stakeholder satisfaction. FM Conway was able to achieve this by sustaining a high level of collaboration throughout the project, resulting in weekly meetings with stakeholders to plan ahead of the programme. 

An additional challenge was the requirement for specific weather conditions to allow the concrete to cure effectively and timely.  As cold weather conditions inhibit the curing time for the concrete and operations were carried out during some of the coldest days of the year, FM Conway designed a heating and ventilation system to sustain the appropriate temperature of five degrees for spraying and curing the concrete. Due to the nature of the work, the team isolated the existing system and created multiple exclusion zones to ensure a safe system of work.  This innovated approach ensured the team incurred no delays due to bad weather.