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Anyone taking a step outside their front door is often right in the middle of noisy demolition or construction: Construction sites characterize our everyday lives, especially in urban areas. It is therefore not difficult to understand that the construction industry is one of the largest consumers of natural resources in the world. At the same time, the demolition of existing buildings and structures generates masses of material that urgently need to be recycled for sustainability reasons alone.

Sustainable concrete building materials and high-performance construction elements

Prof. Libo Yan and his team at the Fraunhofer WKI are tackling these critical issues. In the ReMatBuilt research project, the experts are working with partners from industry and science to develop sustainable concrete building materials and high-performance construction elements based on construction and demolition waste as well as plant-based production residues. The project is funded by the Federal Ministry of Education and Research (BMBF) as part of the National Bioeconomy Strategy.

Practical relevance and rapid implementation are required

The project partners based in Germany and China attach particular importance to practical relevance and rapid feasibility: on the one hand, as an international team, they are concerned with taking account of the global responsibility for bio-based, sustainable business and identifying suitable recycling and production processes for the construction industry. Secondly, they design the resulting products and all upstream process steps in such a way that they comply with the country-specific regulations of both countries. The solutions developed under this maxim can be implemented quickly and thus significantly increase the proportion of renewable raw materials in the construction industry worldwide.

Holistic approach

"The idea of recycling building materials and experimenting with alternative materials from nature is not new. What makes our project unique is its holistic approach," explains project manager Yan. "We are combining our knowledge of the processes and properties of the different materials to understand the chemical, physical and mechanical performance from the micro to the macro scale and are already achieving a very high technology readiness level - an important aspect in terms of practical application."

Less waste, lower resource consumption

If you compare the conventional production and composition of building materials with that of the ReMatBuilt project partners, the multiple advantages of their approach quickly become clear: the experts use so-called building rubble, i.e. old concrete and masonry waste, as well as agricultural residues to produce recycled concrete. They reinforce these components with natural plant fibers such as flax, supplemented by forestry waste products such as wood chips from waste wood.

The sum of the advantages of recycled concrete is impressive

Conventional concrete, on the other hand, contains cement and usually gravel as aggregates. The latter, as an aggregate, is a finite resource whose extraction damages the environment. In addition, it often has to be transported over long distances. Construction waste and waste wood, on the other hand, accumulate in large quantities in the relevant areas all over the world and have hardly been recycled to date. From both an ecological and economic point of view, this is a highly attractive substitute.

Rice husk ash - a more than adequate substitute

The situation is similar with cement. The binder among building materials is made from natural raw materials such as limestone, clay and quartz sand - and causes high carbon dioxide emissions during its production, which is increasingly causing headaches for the industry. Prof. Yan's team has succeeded in identifying a more than fully-fledged substitute: "Rice is the most widely used food in the world. Its husks have hardly been used so far. We have discovered that rice husk ash, which is produced in a special combustion process, is ideally suited as a cement substitute." The test results speak for themselves: the recycled concrete not only conserves finite ecological resources, the building blocks made from it are lighter than their traditional counterparts and impress with increased strength, durability, heat and sound insulation.

Insulation materials also offer potential for sustainable optimization

As part of the project, the experts are also developing insulating materials made from plant waste products such as sawdust, rice and wheat straws as a resource-saving alternative to the currently dominant variants made from petroleum-based plastic, mineral and glass wool or wood fiber. These sustainable insulation boards can be used to connect the finished concrete blocks to form wall systems made of insulated blocks. The experts have also designed composite systems that allow the recycled concrete to be combined with laminated veneer lumber and cross-laminated timber to be used as floor slabs.

Cost-efficient construction despite strict sustainability requirements

The hybrid building elements combine the advantages of conventional concrete and plant-based building materials. They are durable and have impressive mechanical, moisture and thermal insulation properties. They are also easy to process and meet all fire protection requirements. In this way, the project partners are using their solutions to expand the possibilities for cost-effective construction under increasingly strict sustainability requirements - whether for single-family homes or large building complexes.

Successful international cooperation

Project manager Yan is delighted with the successful collaboration between the international project group, which is now being extended thanks to the successes already achieved: "Our work is creating economically interesting prospects - and not just for the insulation and construction industries: in agriculture and forestry, for example, production waste is turned into valuable building materials. In turn, our partners in the fields of recycling and mechanical engineering are developing methods for the best possible extraction and processing of plant waste in order to manufacture the corresponding primary products."

Significant contribution to the reconstruction of Ukraine possible

One aspect is particularly important to Libo Yan: his solutions should benefit people directly and as quickly as possible. This is because the potential of the project partners' results is immense - especially in light of the current global political situation: "We can make a significant contribution to the reconstruction of Ukraine with our work," the project manager is convinced and specifies: "It's terrible, but huge amounts of construction waste are produced here every day. The country is also rich in natural resources and is one of the world's largest exporters of agricultural commodities such as grain - wheat, corn and rice. Against this backdrop, we are currently working hard to put our results into practice. Together with local industry partners, we can play a key role in helping the people of Ukraine to rebuild their country quickly, cost-effectively and sustainably. With recycled concrete building blocks and the corresponding insulation made from natural materials, all of which are available in abundance locally."