On the way to ecological concrete?
Particularly polluting to produce, implement and recycle, cement concrete suffers from a negative carbon footprint, to say the least. There are many inventions intended to enhance the image of concrete, using techniques and materials. much more respectful of the environment.
From hydrophobic concrete to paper bricks
In addition to being polluting, concrete is not necessarily distinguished by its longevity either, being particularly sensitive to water infiltration and CO2 in the atmosphere. Researchers at the University of Wisconsin-Milwaukee looked into the problem and came up with a solution called "Superhydrophobic Engineered Cementitious Composite" (SECC).
The objective was to overcome the shortcomings of conventional concrete, by making it flexible and waterproof. By adding non-woven polyvinyl alcohol fibers, the American researchers got what they wanted. The fibers do not oppose the formation of micro-cracks, which allow water to flow, but prevent these cracks from enlarging. The water glides over the concrete without stagnating, like a bird's feathers. SECC is thus 200 times more deformable than conventional concrete, while being two to four times more resistant than the latter, with a lifespan without intervention estimated at 120 years.
Another solution is to directly produce concrete in a more ecological way. An American start-up, BetR-blok, came up with the idea of mixing cement with recycled paper. This is also the slogan of the company: “Building houses while saving trees”. Cement is mixed with cellulose, made from recycled cardboard and paper, well known for its excellent thermal properties and commonly used as an insulation. The bricks obtained thus constitute excellent thermal and acoustic insulators, in addition to being just as fire resistant as conventional concrete. And in addition to being remarkably ecological, these bricks are very light, with a weight of eight kilos.
Natural concrete made from plants
The very word “concrete” designates more precisely cement concrete, universally produced. And yet, there are other forms of concrete using totally natural materials and therefore much more ecological. As opposed to cement concrete, “earth concrete” (or “natural concrete”) uses materials such as clay, straw, rice bark, flax or hemp fiber.
Linen concrete and hemp concrete offer particularly remarkable specifications, constituting excellent thermal and acoustic insulators, far superior to cement concrete. They also benefit from a much better carbon footprint, flax concrete being particularly distinguished by its superior resistance to cracks caused by the action of water.
These two types of concrete represent a priori a very significant asset for France. Indeed, with nearly 50,000 tonnes of hemp produced in 2013, the country alone accounts for more than two-thirds of world production, far ahead of China (16,000 tonnes), Chile and Ukraine ( 1,450 tonnes). The same goes for hemp, which after almost disappearing from the French countryside in the twentieth century, has made a huge comeback since the early 2000s.
With 75,000 hectares cultivated today, France provides 80% of world production, again far ahead of China. A collaboration between ESITC Caen (Normandy being the 1st linen-producing region of France, and therefore the world) and CMEG society gave birth to "BTONLIN project", which is the first project in the world of marketing a linen concrete. However, there are still points to verify, such as the aging of the material, with the question of the degradation of flax fibers over time in the matrix.