Urban development devours valuable raw materials and emits harmful greenhouse gases. Researchers are working on various solutions: concrete is to become more climate-friendly thanks to bacteria, houses are to be built from reusable parts. And the idea of ??a sponge city should help in extreme weather.
Building has to reinvent itself: Modern urban planning still devours too many valuable raw materials – copper and aluminium, steel and plastic, sand and wood. The Federal Environment Agency (UBA) estimates that 50 billion tons are installed in Germany alone. And only a fraction of it is recycled after use. At the same time, the construction sector emits a particularly large number of harmful greenhouse gases: the UN has calculated that it accounts for almost 40 percent of global CO? emissions.
In order for the architecture of the future to be more sustainable, buildings must be planned and built differently: with innovative concepts and materials – also from science. Architect Dirk Hebe, professor at the Karlsruhe Institute of Technology (KIT), designs buildings that can be completely dismantled and do not produce any waste at the end of their lives, but serve as material storage for future generations. The components are not glued, but inserted, clamped or screwed into each other – so all materials can be completely reused after use. At the same time, the researcher is developing building materials that store CO?, such as stones made from the roots of mushrooms.
His colleague Frank Dehn, head of the KIT institute, wants to improve the most important construction material of all – concrete. The material will also be indispensable in the future. But its carbon footprint needs to radically improve as it is a major driver of global warming. Because its production produces 2.8 billion tons of CO? every year, about eight percent of total global emissions.
The main reason for the high emissions is the cement contained: it serves as a binder in the concrete. Civil engineer Dehn is researching climate-friendly alternatives, for example from the slag from blast furnaces, the ashes from coal-fired power plants or the geo-raw material clay. If concrete is made with it, the production releases significantly less CO?: Dehn believes that the values ??could be halved. In contrast to conventional concrete, its material is also almost calcium-free – and therefore more resistant to heat, moisture and chemical substances. “That makes it particularly interesting for industrial applications.” The first pilot plants with the new concrete are currently being implemented together with the industry.
But building materials expert Dehn is thinking even further: As the energy transition progresses, there will be fewer and fewer ashes and slags that are suitable as cement substitutes. The engineer therefore also wants to use old concrete: Up to now, it has usually been crushed into coarse grains. What remains unused, however, is what is known as crushed sand, a fine granulate that is produced when houses are demolished and construction waste is further processed.
Dehn uses this “concrete dust” as the basic material for a new type of binding agent: it is mixed with certain bacteria whose highly active enzymes bind CO? – this has already been successful in experiments. “That would further improve the carbon footprint of concrete, but our research is still in its infancy,” explains Dehn.
Old concrete that becomes concrete again and even absorbs greenhouse gases: Projects like this are groundbreaking for the architecture of the future, emphasizes Daniela Thrän, bioenergy expert at the Helmholtz Center for Environmental Research (UFZ). Because they strengthen the local circular economy. Thrän has been analyzing bio-based material cycles for years and still discovers untapped potential: cities, for example, could use their waste and wastewater even better if they set up small refineries. These would not only produce biogas for local consumption, but also valuable raw materials for industry – nitrogen for fertilizers, for example. First tests are running in a sewage treatment plant in Stuttgart with the participation of the KIT.
But Thrän sees cities not only as consumers of valuable resources, but also as underestimated producers. Food, for example: the first supermarkets are building fish farming systems on their roofs, for example. Right next to the vats are small greenhouses in which fresh fruit, vegetables and herbs grow. According to the environmental engineer, private houses could also be planned and built in the future in such a way that their roofs and facades bear fruit: for the self-sufficiency of the tenants. The principle is already being implemented in some cities in Latin America, Asia and Africa.
Such small-scale green areas offer even more advantages: they help in extreme weather. Because when it’s hot, they cool their immediate surroundings. And when it rains heavily, they absorb part of the water masses, thus reducing the risk of flooding. More and more municipalities have to prepare themselves for such scenarios in terms of urban planning, explains Bruno Merz, hydrologist at the Helmholtz Center Potsdam (GFZ). With climate change, the number of extreme weather conditions is increasing. “Today, settlements that are not on a river or sea are also threatened by flooding,” says the expert.
The form of construction that has been customary up to now has even favored this negative trend: many communities have sealed their areas in order to drain off water quickly. “We have to turn this basic idea into the opposite and rebuild our towns and villages in such a way that they will hold water for as long as possible in the future,” says Merz. When it rains, parks, roof gardens and green spaces soak up water like a sponge. Surpluses are passed on to hidden tanks – from these reservoirs the green spaces can be supplied later when it is dry. At the same time, these planted areas increase the biodiversity of urban areas.
The principle of the “sponge city” is effective against several consequences of climate change – and can even be combined with solar systems, which are also on the roofs of many houses. Björn Rau, Deputy Head of the Photovoltaics Competence Center at the Helmholtz Center Berlin (HZB), points this out. With his team, he advises municipalities and architectural firms on the use of solar cells on buildings.
“Many planners are not at all aware of how diverse photovoltaics can be used today, not only on roofs but also in facades,” explains Rau. There, they can even be used to generate a particularly large amount of electricity, because multi-storey houses in particular often have much more space on their facades than on the roof. According to a study, such solutions could cover up to a third of current electricity requirements in Germany alone.
Read more: This article first appeared on helmholtz.de.
