What is Rediset cement
A construction world without cement
Habert has long been concerned with the use of local resources, especially in urban areas, where the need is particularly high. One problem that keeps cropping up is the availability of resources. There are more than enough stones under a city to build. But nobody wants a quarry in the city. And where stones are quarried, nobody needs them. The consequences: long transport routes, high transport costs - not to mention the ecological balance. For Habert, the construction industry is less about the scarcity of resources and more about their distribution.
One of the most important local resources for building in the city is the concrete that has already been laid. The ingredients - gravel, sand and cement - can in part be reused after a building has been demolished. To do this, the excavated concrete is first smashed. So gravel and sand can be reclaimed and used in new concrete. The resulting dust consists for the most part of cement, which reacted with water during the production of concrete.
"The recycling of cement is more demanding - but particularly important," states the professor for sustainable building. Because during the production of cement, large amounts of carbon dioxide (CO2): on the one hand when the two raw materials limestone and clay are heated to 1500 ° C and on the other hand through the chemical transformation of the lime. The latter alone produces half a ton of CO per ton of cement2. When recycling in a cement works, the raw material has to be heated up again to be in its original form, but at least this does not produce any more CO2 - provided that heating is climate-neutral.
Less cement, less CO2Emissions
Cement is the ideal binder in concrete, which, when mixed with water, holds gravel and sand together. As part of the National Energy Transition Research Program (NRP 70), Habert heads the “Low-Energy Concrete” project, on which other ETH scientists and research groups from the ETH Lausanne and Empa are also working. The project objective: a concrete product that contains less cement than conventional concrete products, but still has the same properties. In the production of concrete, some of the cement is already being replaced with waste from other industries, such as the steel or coal industries. It has ideal properties and cannot be recycled by the manufacturing industry. Such waste products now replace a good 30 percent of the cement in commercial concrete products.
The researchers now want to double the content of waste products without the mechanical strength of the end product deteriorating. It should stay at 30 megapascals. “This made it possible to build buildings of the same dimensions as today, the CO2-But the balance would be much better, ”says Habert. The team is currently working on characterizing the new concrete with less cement and continuously optimizing it.
One challenge that the researchers repeatedly face is the interaction of the low-cement concrete with other materials, such as the reinforcing steel that is poured with the concrete during construction. If the concrete does not contain enough pure cement, the steel will rust much too quickly. “Such reinforced concrete structures would be less permanent, and that obviously cannot be our goal,” Habert sums up. In addition to optimizing the new concrete, the scientists are therefore also developing alternatives to reinforcing steel. Together they look for rust-free alternatives such as carbon fiber polymers or synthetic fibers. “My focus is on the environmental impact of these materials,” says Habert. He analyzes the CO2-Balance of the various technologies and shows where there are possibilities to optimize the balance.
On the Hönggerberg campus, for example, the “House of Natural Resources” was inaugurated this summer under the direction of Andrea Frangi, which is both an office building and a research laboratory. During construction, the concrete was not poured with steel, but with wood. “The combination of concrete and wood is ideal. Because there is no risk of the material corroding, ”says Guillaume Habert.
Another research approach by Guillaume Habert is far more radical: concrete with clay instead of cement. Because the building material is not heated to a high temperature and thus no chemical reaction is set in motion, it is much more environmentally friendly. But this also has its disadvantages: the mechanical strength is around ten times lower at just 3 megapascals than that of conventional concrete with cement. “That is why this type of concrete is not suitable for the same applications,” says Habert. One possibility could be to use the cementless concrete only for non-load-bearing walls. This alone could significantly reduce cement consumption.
Habert's research group is currently working on not only optimizing the material itself, but also its use on the construction site. If the new type of concrete is poured into the formwork and dries out, cracks are currently still forming. That is why the researchers are working on chemically changing the surface properties of the clay. The goal is that the concrete can be processed within three hours without cement - like the original. In the experiment, cement-free concrete dries out after just 30 minutes. That is far too short for transport and processing. Special formwork with pores that are permeable to water could also help.
But Habert is aware that a new building material only has a chance on the market if the conventional know-how of the construction industry is still in demand. “Hardly anyone is willing to pay more for environmentally friendly construction,” says Habert.
Habert's students should learn that too. That is why he organized the “Grounded Materials” summer school this year together with the Ensag School of Architecture in Grenoble and the TdLab of the ETH Department of Environmental Systems Science. The ETH students dealt with the question: How can environmentally friendly, local materials be brought from Zurich to the local construction industry? During two weeks, students from the departments of Architecture, Materials Science, Environmental Systems Science as well as Building, Environment and Geomatics identified barriers that prevent the growth of local building materials. Based on this, they have developed strategies to make such materials attractive to stakeholders. This did not include the technical key figures such as the strength of concrete or the CO2-Balance in the foreground; rather, the participants moved in the disciplines of sociology, economics and communication.
Guillaume Habert is very satisfied that he has awakened an awareness of such questions in the offspring. "For me as a geologist, resources are first and foremost something physical: in a certain place in a certain amount," he sums up. "But wherever there is an interface between the environment and society, things start to get exciting." How can you use the resource? Where is it located? And where is it needed? Who knows how to deal with her? What does she cost? This summer, his students learned that these are important questions.
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