Concrete, the universal building material of the industrial age, is facing new challenges: The rising global demand for primary mineral raw materials acts as a price driver. And environmental compatibility, climate protection and CO2 emissions have also become important market factors in the building sector. The universal building material of the future must be sustainable. A highly innovative answer to this challenge is now presented by the precast concrete manufacturer Büscher from Heek in Münsterland: High-quality precast concrete elements made from recycled concrete. Büscher is the only company in Germany to date to have received general building authority approval (abZ) from the Deutsches Institut für Bautechnik (DIBT Berlin, German Institute of Building Technology) in June 2021 for precast concrete elements made of recycled concrete with 100 percent natural stone substitute. In the precast elements of the “Büscher wall”, the raw materials gravel and sand are completely replaced by mixed demolition material. The manufacturer is currently demonstrating how much more future potential there is in the Büscher wall by building a three-family house.​

“According to a study by the Bundesverband Baustoffe – Steine und Erden (Federal Association of Building Materials – Stones and Soil), more than 250 million tonnes of demolition material are produced in Germany every year,” says Managing Director Hans-Jürgen Büscher, describing the challenge. “Nevertheless, building rubble has so far mostly been used as filling material in road and underground construction, or it often goes to landfill. Predominantly in the conurbations, but also in northern Bavaria, cities hardly know what to do with the increasing volumes.” So why not recycle building rubble and use it not only in part, but 100 per cent as a substitute for primary raw materials in concrete production?

Due to its general building authority approval, Büscher is allowed to use up to 100 percent recycled aggregate including crushed stone sands similar to type 3 for its precast concrete elements made of recycled concrete in exposure classes XC1 and X0 (dry). According to the standard applied to date, only coarse recycled content of a maximum of 45 per cent for type 1 aggregate and up to 35 per cent of type 2 aggregate is permitted for mixed demolition material.

According to an LCA study, the Büscher group of companies in Heek achieves a 13 percent reduction in its CO2 emissions just by using only recycled material to replace the aggregate. This means that the “Büscher wall” makes a significant contribution to climate protection even during its production.

The possible applications for the “Büscher wall” made of recycled concrete with 100 percent natural stone substitute are manifold. The group of companies from Heek is allowed to build load-bearing and non-load-bearing interior wall elements up to building class 4 from this material. Wall lengths of up to 11 metres and wall heights of up to 3.70 metres are possible.

Building rubble becomes a sustainable building material

The Büscher group of companies came into being from 1961 with the foundation of the concrete plant. There, the company produces precast concrete elements of all kinds. In its sister company Containerdienst Büscher, the group of companies deals with the disposal and processing of building rubble. Since the 1990s, the group of companies of the two managing directors Hans-Jürgen and Wolfgang Büscher and their team of employees have been researching innovative technologies and building materials with a view to sustainable value chains. The idea: upgrading the waste product building rubble into an economically attractive recyclable material. Its use in the production of prefabricated building components can make concrete a sustainable building material of the 21st century.

“This is unique and a big step in the circular economy,” says Wolfgang Büscher. The group of companies also “lives” this circular economy itself in accordance with its slogan “Büscher – Back for the future”. The sister company of the precast concrete plant, Containerdienst Büscher, plays an important role in this. He provides the means of transport for the delivery of building rubble and takes over the professional processing of the demolition material on the company premises. It is sorted, screened, refined and thus recycled into a sustainable raw material for the building industry. The special, certified production process ensures a consistently high quality of the recycled material. The Büscher concrete plant then processes these recycled raw materials in the production of high-quality interior wall elements.

The implementation of this idea requires high standards both in the processing of building rubble and in the production of concrete components. In about eight years of research, the Büscher group of companies has invested a lot of money to develop these standards and to prove their practical suitability in terms of quality and cost-effectiveness. Among other things, the processability of the recycled material as well as the compressive strength and surface quality of the finished product had to be proven. In addition to its own experts, the medium-sized company from Münsterland also worked together with concrete technologists from various universities. The Deutsche Bundesstiftung Umwelt (DBU – German Federal Environmental Foundation) funded the project with 250,000 euros.

In the meantime, the medium-sized manufacturer of precast concrete elements has received several awards for this research activity, including the “Innovative through Research” seal of quality from the Stifterverband für die Deutsche Wissenschaft (Donors’ Association for the Promotion of Sciences and Humanities in Germany) twice. In 2019, the Büscher Group beat 5399 competitors in the competition for Germany’s most important business award. The Oskar Patzelt Foundation rewarded the Heek-based company’s commitment to sustainable management with the “Großer Preis des Mittelstands” (Great Award for Medium-Sized Businesses).

Apartment house as reference object

Now the “Büscher wall” made of 100 per cent recycled sand and stone is proving the potential of this new building material in a practical project. In Heek, the first recycling house of its kind is being built with readyto- paint precast elements made of recycled concrete with 100 per cent natural stone substitute. The building project is to become a “real reference object for innovative building technology” and be completed in December 2022. While the use of precast concrete elements in the construction of residential buildings has so far been considered the exception, the use of elements made of recycled concrete is now intended to prove that with the Büscher wall “individual construction is also possible in a sustainable way”.

Elementary building with recycled raw materials, that is the “Büscher wall”. With their reference project, Hans-Jürgen and Wolfgang Büscher now want to convince the construction industry in particular. The building industry tends to be conservative when it comes to new production processes and products. This makes it all the more important for the two brothers to now make as many architects, municipalities, builders and possible partners from the construction industry aware of the advantages of the “Büscher wall”. All interested parties should be able to see for themselves the possible applications and advantages of the “Büscher wall” at the practical object. By granting licences, the Büscher group of companies wants to promote the supra-regional use of its precast technology. Interested companies can request further information at [email protected]

According to Hans-Jürgen and Wolfgang Büscher, there are enough convincing arguments for the “Büscher Wall”. Finally, the recycled wall elements solve several problems at the same time: it saves on the purchase and transport of scarce and expensive raw materials such as sand and gravel. It offers a genuine sustainable reuse of the demolition material that is flooding the market in ever-increasing quantities. Büscher calculates that around 200 tonnes of recycled building rubble can be used to build a single-family house. Finally, the use of prefabricated concrete elements digitally planned according to customer specifications, produced rationally and resource-efficiently in the factory and delivered ready to be painted can shorten construction times quite considerably.

Economic substitute for primary raw materials

“Our goal is to return the construction and demolition waste generated during the demolition of old buildings to the recyclable material cycle and thus use it as a raw material in the sense of urban mining in order to conserve natural resources,” say the two managing directors. Through the complex reprocessing and reuse in concrete production, the demolition material becomes a sustainable and economic substitute for primary raw materials. While Hans-Jürgen Büscher was sometimes ridiculed for this vision in the past, he now sees himself impressively confirmed by the results of years of development work and the DIBt approval: “With our process, precast concrete elements can be produced with 100 per cent natural stone substitutes”. All that needs to be added is water, cement and the additives required for the respective recipe. “The entire part then consists of 80 per cent recycled materials. This high percentage is unique.”