In the realm of tunnel construction, Benoit De Rivaz is a name that stands out as a seasoned professional with over 30 years of experience. Currently serving as the Global Technical and Business Development Manager for Bekaert’s Underground segment, Benoit has witnessed the passion of tunneling experts and their dedication to modernize construction techniques, materials, and promote low-carbon solutions. In this interview, we have the privilege of gaining insights from Benoit as he addresses crucial questions on the sustainability of tunnel construction.
Benoit De Rivaz: Underground space plays a vital role in sustainability for various reasons. It offers a solution to the limited surface area available for urban expansion. One of the most significant impacts is on transportation. Underground networks enable efficient and rapid mass transit, which can help alleviate surface congestion and reduce carbon emissions. Additionally, underground space is essential for infrastructure, including networks of pipes for delivering fresh water and sewers for wastewater treatment. This hidden infrastructure is fundamental for urban areas, as it ensures the health and well-being of city residents. Moreover, it accommodates the extensive network of cables and service stations necessary for modern communication systems, which are integral to our daily lives.
Benoit De Rivaz: Absolutely, decarbonization in tunnel construction is not only possible but crucial from a sustainability perspective. Currently, nearly 70% of embodied carbon in tunnels is attributed to concrete linings. To tackle this issue, we have innovative solutions at our disposal. Steel fibers, for example, can play a pivotal role. By reducing the required thickness of segment concrete by 2 to 3 cm, we can save up to 50% in steel and concrete compared to traditional reinforcement, especially in precast lining. This means substantial reductions in material usage and, ultimately, a reduction in the carbon footprint. In a typical metro tunnel of 10 km, fiber-reinforced precast segments can save up to 5,000 tons of steel, resulting in an impressive 10,000 tons of CO2 savings.
Benoit De Rivaz: Portland cement is a significant contributor to global CO2 emissions and is widely used in tunnel construction. It's imperative that we minimize its role, no matter what. One approach is to partially replace it with a new generation of binder materials. These innovative binders are low in carbon and have a smaller environmental footprint. While certain low-carbon binders might not be universally available, steel fibers, on the other hand, are accessible almost everywhere. Implementing them can be an excellent start towards reducing the carbon impact of tunnel construction. To illustrate, consider the Doha Metro, which used steel fibers - if it had been built like the one in Copenhagen that used traditional reinforcement, it would have resulted in 400,000 tons more CO2 emissions.
Benoit De Rivaz: The development of permanent spray concrete lining is an exciting frontier in tunnel construction. By employing alternative methods, such as permanent shotcrete liners, and enhancing mix designs, we can achieve a significant reduction of up to 74% in CO2 emissions. The present approach of utilizing excessive structural design, involving cast-in-place concrete or other lining structures, has adverse effects on costs, excavation volumes, construction duration, and CO2 emissions. Recent projects in Norway, India, and Australia are clear demonstrations of the potential for change. Concrete savings through the use of technologies like Dramix® fiber-reinforced spray concrete are set to be a driving force for further developments in permanent spray concrete lining, advancing sustainability in tunnel construction.