Concrete repair, carbon fibre wrap, bridge refurbishment – Edinburgh North Bridge

Freyssinet was appointed to deliver concrete repairs and protective coatings to the bridge’s concrete deck and transverse girder beams. The first phase, starting in August 2020, focused on concrete repairs. The second phase, which started in 2023, involved applying carbon‑fibre wrap to all transverse girders and an anti‑carbonation coating to the deck soffit.

Edinburgh North Bridge comprises three equal spans – north, central and south, divided into five bays: A, B, C, D and E. Each span measures approximately 55m long by 23m wide and contains 120 transverse beams. While not all beams required repair, all were scheduled to receive carbon‑fibre strengthening. In 2022, the deteriorated condition of Bay C led to its removal from Freyssinet’s scope, with Balfour Beatty constructing a new deck in situ.

Freyssinet’s scope of works included:

• Join surveys to identify scope repairs in each span
• Installation of containment – to collect wastewater and concrete debris
• Hydrodemolition by Aquaforce Concrete Services (Freyssinet subsidiary) to break out defective concrete, including wastewater treatment on site
• Trimming concrete edges and around rebar
• Continuity testing and hand tying rebar with stainless steel wire x Installation anodes XP2 in repairs
• Additional rebar and mesh installation in the transverse beams, including welding rebar to existing structure
• Re-instatement of concrete by spray concrete
• Surface preparation prior to applying coatings
• Application of CFRP wrap to transverse beams
• Application of anti‑carbonation paint to bridge deck soffit
• Installation of a cathodic protection monitoring system

Cathodic Protection System 

A galvanic cathodic protection system was installed to protect the steel reinforcement within the repaired concrete. Early checks showed that the existing reinforcement had poor electrical continuity, so every bar and link had to be cleaned and reconnected using stainless steel wire. Switching from hand grinding to dry grit blasting made the cleaning process faster and ensured reliable electrical contact. Galvanic anodes were placed within the repair areas, and several locations were set up for long-term monitoring. Atkins prepared the detailed design, and final monitored areas were confirmed on site after half‑cell testing.

Seven monitored sections were installed in total, two in the South Span, two in the Central Span, and three in the North Span. Each section contains 12 linked anodes, separate reinforcement.

Carbon fibre wrapping of transverse girder beams

Transverse girder beams were wrapped in carbon fibre fabric to strengthen the structure and prevent any future debris from falling onto the station below. An additional resin coat was applied over the fabric to improve long term durability, recognising both Scotland’s weather conditions and the limited access for future maintenance beneath the bridge.

Environmental conditions were closely monitored during installation. Moisture, humidity and dew point levels often fluctuated within the scaffold encapsulation, so ventilation and heating were introduced when needed to maintain the minimum application temperature. Throughout the works, newly painted ancillary steelwork was protected using foam and tape to avoid damage during carbon fibre installation.

Application of anti-carbonation coating

An anti-carbonation coating was applied across the entire bridge deck soffit, with a 50mm overlap onto the girder beams, to protect the concrete from future carbonation. Before coating, all sharp edges and surface irregularities on the soffit and beams were removed. Where required, electric concrete planers were used to achieve a smooth, consistent substrate. The deck soffit was then washed using a bowser jet wash to remove dust and left to dry fully. The system consists of a water-based adhesion primer, followed by a plasto elastic protective topcoat.

Challenges

Access within the scaffolding – Access beneath the bridge deck was constrained by the curved steel arch structure and the dense, complex scaffolding required to support the works. This made operations such as hydrodemolition and spray concrete particularly challenging. Productivity was significantly lower than the industry norm, as debris could not be removed using mechanical systems. All material handling had to be done manually, often in awkward positions and confined working areas. Although not classed as a confined space, the environment was physically demanding, and safety remained Freyssinet’s top priority throughout.

Containment installation for hydrodemolition waste – All wastewater and debris from hydrodemolition had to be fully contained to protect Waverley Station directly below. Due to the maze of scaffold poles, it was impossible to install a single continuous waterproof platform. Instead, a multi-level containment system was created, using cascading platforms and electric pumps to collect and remove wastewater. This required significant time, planning and labour resources.

Permanent baffle curtains were also installed to create sealed, waterproof barriers over several scaffold levels. These were essential to prevent wastewater or debris from reaching the live electrified railway lines, pedestrian routes, station offices, and critical equipment beneath the bridge.

Despite these challenges, the client praised the quality of Freyssinet’s work – particularly the spray applied concrete repairs and the installation of carbon fibre reinforced polymer (CFRP), which has strengthened the historic structure and extended the bridge’s service life.