The Gotthard Base Tunnel is a remarkable masterpiece of modern engineering. Stretching 57 kilometers through the depths of the Swiss Alps, it is not only the longest railway tunnel in the world but also the deepest. To maintain a consistent rail gradient, engineers had to dig the tunnel as deep as 2.3 kilometers beneath the mountains.
The tunnel consists of two single-track tubes for train traffic, accompanied by passenger-related infrastructure, shafts, ventilation and safety tunnels. Altogether, the complete tunnel system spans over 152 kilometers, and approximately 28.2 million tons of rock were excavated during its construction.
This record-breaking project is also considered one of the largest environmental undertakings in Europe. Its impressive achievements in construction, logistics, and sustainability are largely attributed to the innovative use of advanced, durable, and multipurpose concrete.
The Gotthard Tunnel was inaugurated in 2016, creating a high-speed rail connection between the towns of Erstfeld in the north and Bodio in the south of Switzerland. This route has significantly reduced travel time between Milan and Zurich by about one hour.
The Gotthard Tunnel serves as a cornerstone of the “Alpine Initiative” – a policy adopted by Switzerland in 1994 to protect the country’s natural landscapes from the negative impacts of road traffic. By shifting freight and passenger transport from road to rail, the tunnel has significantly reduced the heavy, noisy, and polluting truck traffic in the Alpine region.
In February 2018, the project was awarded the European Railway Award for its crucial role in modal shift from road to rail. It is estimated that the tunnel saves around €120 million annually in environmental costs.
To meet the environmental goals of the Gotthard Base Tunnel project, the engineering team had to overcome one of the most demanding aspects of underground construction: transporting concrete under extreme conditions. The concrete needed to be moved across long distances deep underground, where ambient temperatures were much higher than at the surface—without setting prematurely or losing its performance characteristics. This was critical because the concrete had to remain fully workable to allow precise pumping and placement.
The project also operated under an extremely tight schedule, leaving no room for delays. Adding to the complexity was a strict requirement to use 100% recycled aggregates sourced from the tunnel excavation itself. This eliminated the option of using ready-made materials from external suppliers and required the construction team to process raw materials directly from the mountain, transforming them into usable concrete on-site.
Meeting these challenges required a meticulously planned approach, advanced engineering, and innovative materials science. The solution came in the form of a new formulation of specialty cement, which enabled the production of ready-mix concrete with enhanced durability and extended setting time. The resulting concrete had a setting time of 11 hours—almost twice that of conventional mixes. This extended workability optimized transport from the mixing plant to the installation sites and allowed for efficient delivery via rail systems.
This innovation not only ensured high-quality construction but also eliminated the need for additional concrete plants, thereby minimizing the project’s environmental impact.
The engineering response to the challenge of transporting concrete under the extreme conditions of the Gotthard Tunnel came in the form of an advanced formulation of a specialty cement, enabling the creation of a high-performance ready-mix concrete (RMX). This innovative concrete, designed with an extended setting time of up to 11 hours—compared to around 6 hours for conventional mixes—maintained its fluidity and workability over long distances and at elevated underground temperatures, without compromising its mechanical properties.
The prolonged setting time was a critical advantage in transporting the concrete from the mixing plant to the installation site. It allowed the concrete to be delivered rapidly and efficiently via rail lines into the tunnel. This method not only accelerated construction but also eliminated the need for additional on-site batching stations. As a result, the project avoided extra resource consumption, waste generation, and carbon footprint—an important step toward meeting its sustainability goals.
Taking this approach even further, the project team recycled over one-third of the 28.2 million tons of excavated rock as aggregate in concrete production. This innovative strategy relied on local geological materials and was only made feasible by the development of a customized, adaptive, and durable cement formulation. According to Fabio Pellegrini, International Tunnel Manager at LafargeHolcim:
“This project demonstrates how innovative, sustainable, and adaptable cement and concrete solutions can directly address environmental challenges.”
Pellegrini explains that the new cement formula enabled the production of a highly durable concrete with excellent mechanical strength, specifically designed to withstand the extreme conditions of underground construction. Beyond its impressive technical performance, the concrete was engineered to support a service life of at least 100 years, making it a shining example of how engineering innovation and environmental responsibility can work hand in hand in one of Europe’s most ambitious infrastructure projects.
In a project as vast and complex as the Gotthard Base Tunnel, the intelligent management of excavated materials played a crucial role in achieving environmental and sustainability goals. According to Fabio Pellegrini, one of the key factors behind the project’s success was a shift in mindset—viewing excavated rock not as waste, but as a valuable, recyclable resource. This forward-thinking approach paved the way for effective on-site resource utilization and completely eliminated the need for new material extraction.
The result of this progressive strategy was the complete avoidance of landfilling excavated material, thereby preventing the environmental degradation associated with waste disposal or transportation. By using locally sourced excavation material, the project fully eliminated the need for mining natural aggregates, achieving a dual benefit of cost reduction and reduced strain on natural resources.
To further minimize the project’s carbon footprint, the transportation of recycled aggregates was carefully planned. Instead of relying on diesel trucks that emit high levels of pollutants, the excavated materials were moved via environmentally friendly conveyor belts to the concrete mixing plant. This solution not only increased operational efficiency but also significantly reduced greenhouse gas emissions, making the project a true model of sustainable construction at an unprecedented scale.
Thanks to innovations in advanced cement and concrete technology, the Gotthard Base Tunnel—one of the world’s most ambitious infrastructure projects—not only achieved its environmental objectives but is also set to endure as a resilient and sustainable infrastructure solution for generations to come.
