Between the unauthorised rubbish dumps fed by building sites and greenhouse gas emissions generated by producing cement, the construction sector would appear to be an absolute champion of pollution. And yet, solutions already exist to enhance the value of most of the construction materials and reduce their carbon footprint.
Construction waste represents nearly three quarters of all the waste produced in France, and only the value of half of that amount is enhanced today. It is an understatement that waste from construction and public works are a far cry from being a model of ecological transition, particularly as part of it is quite simply thrown anywhere, feeding unofficial waste dumps, which can be huge. In the face of this, Brune Poirson, Secretary of State for Ecological and Solidarity transition, announced last September the introduction of measures designed to encourage the collection and recycling of this waste: from 1 January 2022, professionals will be able to leave their waste in rubbish dumps free of charge (on condition that the waste can be sorted by the type of matter, e.g., iron, wood, rubble…). Meanwhile, the number of collection points should be stepped up, and sanctions against unofficial waste dumps strengthened — the cleaning of these dumps costs local authorities between €340 and 420 million per year. This will increase the chances of moving closer to the objective set by the European directive adopted in 2008, which imposes an enhancement rate of 70% of construction waste by the 2020.
Boosting the re-employment of recycled waste
The problem: while building sites and artisans increasingly take their waste to rubbish dumps, industries still struggle to incorporate them in their production. “It is important that we integrate an ever-increasing amount of recycled matter in everything produced or constructed. We notably experience difficulties re-employing wood because there are still too few outlets by comparison with what we are able to sort,” she explains. “It’s a question of adapting: if an industry is only able to integrate 15% of the recycled matter, it will not take more than that.” »
« It is important that we integrate an ever-increasing amount of recycled matter in everything produced and constructed. »
Technically, this rate could already be broadly achieved: at the Bonneuil-sur-Marne (Val-de-Marne) in France, Veolia's sorting centre opened in April 2019, it reached over 80%. With an annual capacity to take in 250,000 tonnes of waste a year, including 25,000 tonnes for the waste dump dedicated to artisans, this sorting centre absorbs part of the waste of construction sites generated by the work under way on the Grand Paris project, the quantity of which should reach 43 million tonnes in 2026. After the sorting phase, the recovered materials (metals, hard plastics, rubble, plaster…) supply industries with recycled raw materials. Among the 20% of remaining materials, half is subject to energy enhancement, a process of thermal treatment allowing for the recovery of heat produced by the combustion of certain elements contained in the waste, which could then feed into an urban or industrial network with certain elements contained in the waste. According to Valérie Gauthier, director of Process and Recovery at Veolia, in the Ile-de-France region, sorting plastics is the main margin of development to increase the rate of value enhancement.
Fly ash and biomaterials: towards eco-construction
In the beginning, the design process of our buildings also remains to be desired – beginning with cement, for which the industry represents no fewer than 7% of the world’s emissions of greenhouse gas, according to the International Energy Agency. The reason for this is the decarbonization of limescale, its main raw material, which is heated at temperatures that can reach up to 1450°C…
There is no need for thermal power plants to produce less polluting construction materials. Among these “biomaterials” are: clay-based concrete, bricks from recycled waste, and even wood, straw and hemp, which make very good natural insulating materials. Thanks to Building Information Modelling (BIM) technology, it is now possible to assess the environmental impact and energy performances of a construction project thanks to a 3D digital layout, and even to think about the end of the building’s lifespan, by diagnosing the waste before demolition to facilitate its valorisation.
In the Czech Republic and Poland, where thermal power plants supply a large part of the electricity used, cement comes partly from enhancing the value of “non-combustible “fly ash” or “flue ash” fine particles of burnt fuel (which also constitute toxic waste). “Fly ash can be incorporated in the production of concrete and cement, but also mortar, plaster and adhesives,” explains Magdalena Kempinski, Veolia’s Director of Communication in Poland. “They notably improve the manageability of plastic concrete, and the solidity and durability of hardened concrete”. Above all, they reduce the carbon footprint associated with the production of concrete by 25% to 30%.
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