2023-09-26 04:39:19
Switzerland is a large consumer of concrete, with 584 kg per inhabitant per year, double that of the United States and France. In forty years, it has concreted an area equivalent to Lake Geneva. But concrete is criticized for its CO2 emissions (8% of global emissions). The industry is therefore looking for alternatives.
The world’s leading concrete company, Holcim is the most polluting Swiss company in the country. At its production site in Geneva, it produces nearly 600 m3 of fresh concrete for the canton every day.
Under pressure to reduce its CO2 emissions, the company recently started recycling concrete waste, which would otherwise simply be piled up in landfills.
“We recover reinforced concrete, a mixture of concrete and steel. All these materials are reused; the steel is sent to a special channel to be recycled, while the concrete is reused in the production of concrete,” explains Romain Roger, director of the Geneva market of Holcim Switzerland on Monday in the RTS show basik. The concrete blocks are crushed to obtain granules and sand, then reintroduced into a mixture with cement and water.
But cement, which is used to “glue” the components of concrete, is the element that emits the most CO2 during the manufacture of concrete. The production of cement involves a double emission of CO2: first to produce the heat necessary to heat the limestone, the basic element of cement, to almost 1400 degrees, then during the chemical transformation of the limestone at this temperature.
Cement is the element that emits the most CO2 during the manufacture of concrete. [RTS]
10% reduction in emissions
Holcim’s recycled concrete contains as much cement as conventional concrete, only the aggregates come from recycling. But for Romain Roger, it is a first step: “We manage to reduce CO2 emissions by 10% compared to standard cement […]. Currently, we produce between 10% and 15% recycled concrete, and we plan to reach 25% by 2025.” Despite a slightly higher price, 2% to 3% compared to traditional concrete, the recycled version still remains largely a minority in the company’s production.
However, many less polluting alternatives than recycled concrete exist. At EPFL’s Building Materials Laboratory, Professor Karen Scrivener has dedicated her career to concrete research and developed a formula that significantly reduces the amount of concrete used, called LC3 concrete.
Among the many possibilities evaluated by the professor and her team to reduce cement emissions, the best solution consists of using calcined clays to replace part of the cement. “We heat them to 800 degrees, about half the temperature needed for cement, which reduces pollution from the fuel, and there is also no decomposition of the limestone rock. With this mixture, we “We can reduce CO2 emissions by 40% compared to standard concrete. This has a big impact on a global scale,” she explains.
Karen Scrivener does not seek economic profits with her invention, because the LC3 concrete formula is royalty-free worldwide. Currently, nine cement plants out of around 3,000 in the world use it, and twenty to thirty more will begin production in the coming years.
Reuse concrete
Other researchers are also working to find less polluting concrete formulas. But given the impossibility of producing completely clean concrete, some are turning to reusing existing concrete.
Damien Varesano, a Geneva engineer, is working on this approach. “The old Fiat factory is being completely demolished. It’s a huge reinforced concrete building, and in this demolition we are trying to introduce a little reuse, sawn concrete, to reuse it for others projects,” he says.
In order to ensure that the concrete and the steel reinforcements that make it up are in good condition, it is necessary to carry out a series of tests. These tests aim to collect information on the structural strength of the concrete to determine how it can be used in the future. Although these tests are expensive, Damien Varesano assures that with a sufficient quantity of material, the cost of recycled concrete will be comparable to that of fresh concrete.
The main challenge with reuse is the logistics of ensuring the right block is in the right place. To facilitate this process, Damien Varesano created the exchange platform REUSEaimed at coordinating reuse stakeholders in the region.
Earthen
Other players are exploring forgotten alternatives to concrete, such as raw earth, “which has ecological and aesthetic advantages”, according to architect Olivier Krumm. Although raw earth cannot replace concrete in all cases, it emits between five and seven times less CO2 than traditional concrete. The objective is not to completely replace concrete, but to reduce its use, underlines Olivier Krumm.
Ultimately, there is no miracle solution to do without concrete entirely. However, whether through recycling, the use of clay, reuse or a return to traditional materials, many complementary solutions are available.
Micaela Mumenthaler and Valentin Tombez
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