BESSAC : wins gold at the 2025 ITA Tunneling Awards!
At the 2025 ITA Tunneling Awards, organized in early October by the International Tunneling and Underground Space Association (ITA), Bessac won the gold medal in the “Technical Innovation of the Year” category. This prestigious award recognizes a world first: the use of EXEGY® ultra-low carbon concrete segments incorporating metakaolin on the CLB package of the Toulouse metro extension. This project is a perfect example of Soletanche Bachy’s environmental roadmap!
The CLB pckage of the Toulouse metro extension includes underground work to connect Line B to the new Line C.
This work includes two shaft structures for the entry and exit of the tunnel boring machine, enabling the excavation of a 250-meter-long twin-tube tunnel with an internal diameter of 4.66 meters. This tunnel extends the existing Line B from Ramonville station, allowing it to pass under the Canal du Midi.
The tunnel layout has very tight curves and steep gradients at the start and exit. These parameters require the use of a compact machine, namely a point-attack tunnel boring machine.
EXEGY® ultra-low carbon concrete wins award at the ITA Tunneling Awards 2025
The BESSAC / GTM SO TP GC / SOLETANCHE BACHY consortium initiated an environmentally friendly approach by incorporating the principles of “recycling” and “short supply chains” from the tender phase onwards.
For the construction of the tunnel segments, the team achieved a world first: the validation and implementation of a very low carbon concrete formula based on limestone filler and metakaolin. In this EXEGY®L+C3 concrete, 55% of the clinker has been replaced by these mineral additives.
Its mix design was developed by the VINCI Construction and Soletanche Bachy materials laboratories using a performance-based approach, enabling the company to offer innovative concretes with significantly reduced clinker content, subject to testing to qualify their strength and durability. This approach required the agreement and support of all those involved in the project: the project owner and their assistants, the main contractor, the supervising office, the precast manufacturer, and the site operators.
Challenge accomplished! The tests qualified a concrete that meets the expected technical performance requirements: strength class C40/50 and exposure classes XC2 and XA1, at a price equivalent to conventional concrete while emitting approximately half the CO2.
What’s more, the materials selected for the manufacture of the concrete were sourced locally exclusively in Occitanie!
This innovation is part of VINCI Construction’s commitment to achieving 90% low-carbon concrete on its construction sites in France and around the world by 2030.
Congratulations to the Bessac teams for this success!
