Steel bridges, reinforced and prestressed concrete bridges, composite steel‑concrete bridges: civil engineering structures, whatever their construction method, undergo transformations over time. The ageing of the materials of which they are made, and the evolution of the constraints to which they are subjected, justify appropriate maintenance. Repairing, reinforcing and adapting the existing heritage thus represent a considerable technical and economic challenge. At a time when a region’s dynamism depends in part on the quality of its transport infrastructure, Bouygues Travaux Publics offers, under the VSL France brand, an integrated service for monitoring, repairing and reinforcing engineering structures:
- Concrete repair and protection.
- Reinforcement with composite materials.
- Reinforcement by additional prestressing.
- Computer-assisted jacking.
- Replacement of support devices.
- Upgrading of safety systems.
In this restoration market, Bouygues Travaux Publics provides its expertise in terms of risk management and working on occupied sites under severe operating constraints. By managing all the interfaces, we ensure the consistency of the entire project for our clients.
Execution of repair work on prestressed structures and supports of the coastal road
An iconic road on the Marseille coast, the Corniche Kennedy suffers from repeated attacks of sea spray and sea air on its reinforced concrete structure. After renovation work begun in 1999 to make the surface more watertight and consolidate part of the viaducts, a new restoration programme was launched in 2008 on the four remaining structures and corbel supports: reinforcement by additional prestressing, repair of the concrete and repair of other equipment. In 2018, new repair and reinforcement work again started to be undertaken on the part of the road above the sea: repair and reinforcement of the reinforced concrete brackets, replacement of the existing parapets and benches with new ultra‑high‑performance fibre-reinforced concrete (UHPC) elements containing organic fibre and replacement of the existing slabs with new prefabricated ones. The reinforcements of the concrete brackets were protected by the putting in place of an impressed current cathodic protection system.
Widening of the Pont National as part of the extension of the T3 tramway line
The widening of the Pont National was an opportunity to embellish and reinforce this structure built in 1852 and 1853 by the engineers Couche et Petit. 188.5 metres long and 34 metres wide, the Pont National is an essential transportation artery for the capital’s 12th and 13th districts. It comprises, downstream, a masonry structure carrying the Petite Ceinture (Little Belt Railway) and, upstream, a reinforced concrete structure carrying the Boulevard des Maréchaux ring road. The operation consisted of modifying the profiles across the upstream part to allow the installation of the tramway platform, reinforcing the existing structures to support these new loads with the construction of a new reinforced concrete slab to replace the upstream side deck, and widening the structure with a footbridge for pedestrian and cyclist traffic. All this in a dense urban environment with no interruption to Parisian traffic.
Reinforcement of the bridge piers
Inaugurated in 1977, the Brotonne Bridge has a span of over 300 metres, a world record for a cable-stayed structure at the time. But this colossus suffers from the climate; as the temperature differences between the inside and outside of its hollow piers can reach up to 15°C which resulted in cracks in both of them. Reinforcement work is aimed at reducing these scars and preventing their formation. The cracks were treated by injection. Peripheral ribs of reinforced concrete were created inside the piers with deferred stitching to the existing walls. Evenly distributed over the entire height of the piers, composite fabric rings have been glued to complement this reinforcement. Some areas had deteriorated and were repaired by patching with special mortars and passivation of the reinforcements. After these ad hoc repairs, a complete restoration of the external facings, visible to the public, was carried out. This coating consists of a modified hydraulic binder.
Upgrading work on the Grand Pont in Thouaré-sur-Loire
Over the Loire, corrosion had taken its toll on the 400-metre-long Grand Pont de Thouaré, built in the 19th century. To restore the structure and ensure its future, Bouygues Travaux Publics gave it a total upgrade. The original brick vaulted carriageway has been replaced by an Ultra High-Performance Fibre reinforced concrete slab resting on new steel bridge components. This material made it possible to design a slab only 9 centimetres thick, resulting in a saving of 1,500 tonnes compared to the use of traditional concrete. As the steel structure had been affected by corrosion in several places, it was reinforced by the replacement of certain structural components. Anti‑corrosion protection was applied after complete stripping of the framework. New railings and walkways were also installed. The more contemporary blue finishing coat brings the structure right up date for the 21st century.
Crack repair and overall restoration of the bridge
The Sainte-Croix-du-Verdon Bridge has linked the departments of Var and Alpes-de-Haute-Provence since 1972. The quality of the materials at that time, as well as the means of calculation available, did not make it possible to anticipate the phenomena of concrete creep and tension losses in the prestressing cables. In order to reinforce the deck structure, eight additional prestressing cables anchored at the abutments were planned over the entire length of the deck. The transverse structure was reinforced by pairs of prestressed bars. The central span was reinforced with strips of carbon fibre fabric distributed around the box girder. Each crack was then treated by a sealing and resin injection process. At the same time, the superstructures were also restored: waterproofing of the road surface, replacement of pavements, pavement joints and guardrails. In addition, anti-intrusion devices for chiropterans (bats) and replacement nesting boxes for swifts were installed.
Repair and protection of access viaducts
At 3,356 metres in length, this structure consisting of two concrete access viaducts and a cable-stayed steel deck, remains the longest bridge in France. To reinforce the structure of the girders of the south and north viaducts, Bouygues Travaux Publics optimised its methods by designing floating pontoons which, hoisted under the spans, served as working platforms. These barges were used to transport equipment, materials and waste. The structural reinforcement of the girders was carried out using an isostatic solution of additional external prestressing. The application of strips of carbon fibre composite material locally reinforced the rebar reinforcement. Finished in 2013, the work on the south viaduct was complemented in 2020 with new operations on the north viaduct: installation of a permanent intrados footbridge, repair of the beams, struts and underside of the slabs, application of a coating on 22 spans, protecting the concrete from sea spray and sea air, thus limiting corrosion of the reinforcements.