Materials circularity

The brick production process is less energy-intensive than other prevalent building materials (i.e., concrete or steel). However, the overall environmental impact of brick production and use depends mainly on local conditions, such as the availability of natural resources, production methods, and transportation. Therefore, it is crucial to maximise the use of brick from local sources and, where possible, reuse old bricks. Reusing bricks requires cleaning from mortar, which fortunately can occur mechanically without using water and additional chemicals, as in the case of Gamle Mursten’s CE-certified bricks.

• Direct reuse of brick masonry: brick masonry can be used directly as panels, such as in the case of the Resource Rows project in Copenhagen by the Danish company Lendager.
• Direct reuse of reclaimed bricks: a brick can undergo a reclamation process that involves removing old mortar or paint, cleaning it, and then reusing it in construction, as in the case of the Ravensburg Art Museum (Germany), which used bricks from the demolition of a 14th-century monastery, thereby embedding the new building in the historic landscape of the city. A similar example of preserving cultural heritage through using demolition bricks is the Historical Museum in Ningbo (China), where the façade was made of bricks dating back a thousand years.
  

  The possibility of recovering bricks depends highly on the mortar used. Cleaning bricks from modern mortars (fast-setting and hard-to-get-off) often damages the bricks and is more time-consuming than when a lime mortar is used^[1].

• Use of bricks to build drainage systems: bricks can be used to build drainage systems in gardens, parks, or other green spaces.
• Recycling crushed bricks: crushed bricks can be used, for example, as aggregate for new construction materials, such as concrete mix, or, ultimately, as backfilling material in, for instance, road construction

The toll concrete takes on the environment is mainly related to cement production, an energy-intensive process resulting in considerable greenhouse gas emissions. According to the Global Cement and Concrete Association, cement production accounts for about 5-8% of global greenhouse gas emissions. To reduce the energy intensity of the cement production process, in addition to process automation, proper maintenance, and operation of machinery and equipment, several technologies can be applied (e.g., more efficient grinding technologies or the use of waste heat to generate energy). Additionally, clinker can be replaced with other materials (e.g., calcinated clay)^[2], or cement can be partially replaced, for example, with waste from combustion processes (i.e., slag or fly ash)^[1].

• Direct reuse of concrete elements retaining their original function: elements that are free of design, technological and functional defects can be reused as part of their original function, as exemplified by the use of existing walls, basement ceiling, elevator shaft, and entrance walkway in the Brunnerstasse 9 project by Brandlhuber & Emde & Burlon in Berlin, or the use of a large slab in a bungalow project in Berlin by Carsten Wiewiorra.
• Direct reuse of concrete elements in other than its original function: concrete elements can also serve a new function, such as using concrete blocks as garden and sidewalk slabs, as was the case with the Urban Outfitters HQ project by D.I.R.T. Studio in Pennsylvania, USA.
• Recycling of crushed concrete: crushed concrete can be used as a source of unhydrated cement^[2], waste aggregate^[3] (which can be used for both structural and non-structural elements, such as drainage), and, ultimately, as a base for roads, parking lots or filling pits on a construction site^[1].
  

  In the case of recycled crushed concrete, one of the biggest challenges today is maintaining the required parameters of the final product. Therefore, recycled concrete is often used in road construction or for non-load-bearing elements^{[1, 3]}.

The environmental impact of glass production is associated predominantly with raw materials consumption (i.e., quartz sand, sodium carbonate, and calcium oxide) and high-intensity production process resulting in pollutants emission (e.g., greenhouse gases, nitrogen oxides, sulfur oxides). Additionally, due to their fragility, the transportation and assembly of glass components require more vehicles and special equipment and, thus, more fuel-consuming. Lastly, glass affects energy consumption during the building operation as its relatively low thermal insulation can amplify heat loss and increase energy demand for heating. Glass is, however, a material that can be easily recycled without losing its original properties. Recycling glass can require much less energy than manufacturing it, so the greater the amount of glass recycled, the less energy is used to produce new glass, minimising its environmental impact.

• The direct reuse of glass elements: direct glass reuse is often associated with technical problems due to glass fragility and disassembly problems. However, glass elements are being used successfully in construction, as in the case of the facade and roof made of glass from end-of-life vehicles at the Glass Chapel in Masons Bend (USA).
• Production of glass components and products from cullet: cullet can be recycled many times, allowing the production of new products, such as facade components, balustrades, doors, windows, and lighting, for example.
  

  It is essential to sort glass waste properly, considering its colour, type, and production method. Proper sorting ensures the quality of the material during processing as the glass batch can become contaminated without proper sorting, and thus its quality can deteriorate significantly.

• Production of insulation from cullet: cullet can be used in producing insulation materials, such as glass wool or foam glass, which reduce energy consumption in buildings and improve room acoustics.
• Production of building materials from cullet: cullet can be used as a substitute for raw materials used in the production of building materials, for example, as a substitute for aggregate in the production of concrete or as a source of silicon in the production of ceramic products, or bricks^[1].

The steel production process generates air pollutants, such as, for instance, sulfur dioxide, nitrogen oxides, and particulate matter, waste (e.g., steel slag), and is associated with significant water consumption. Moreover, the process is energy-intensive, and its general energy consumption is estimated at 10 GJ/t of steel produced (exact values depend on the type of steel, its finish, application etc.).

• Direct reuse of structural steel: structural steel is a durable material that can be reused in several ways, both in its original and modified forms (e.g., by resizing – cutting). It makes steel elements an attractive option for reuse as, for instance, beams, roof cladding, pipes, stairs, or decorative elements^[1]. An example is the facade made from used steel sheets at the Kringloop Zuid recycling centre in Maastricht, the Netherlands, or the use of steel elements from an old vehicle hall in constructing the Almere Recycling Center in Almere, the Netherlands.
  

  The standardisation of steel element dimensions facilitates direct reuse.

  Steel can also be used to construct buildings designed for disassembly and reuse, such as Pre-Engineered Steel Buildings (PEBs).

• Recycling scrap steel: steel can be recycled and reused to create building components.
  

  Steel scrap processing still takes a toll on the environment, so to further reduce that, direct reuse of steel elements in their original form (e.g., building load-bearing structures, facades) or steel regeneration from composite structures (e.g., steel-concrete composite structures) should be considered^{[1, 4, 5]}.

• Reusing steel in interior design: steel can be used to create furniture or other furnishings, giving any space an industrial yet modern look.

Wood material production usually has a lower environmental impact than conventional materials (i.e.,  concrete or steel) as its processing is less energy-intensive. Similarly, its use in construction is associated with a lower toll on the environment as it can reduce the building’s energy consumption due to its excellent insulating properties preventing heat losses. Nevertheless, emphasis should be placed on sustainable forest management, which minimises the negative impact of the timber industry on biodiversity and forest resources.

• Direct reuse of wooden elements: wooden elements, such as window frames, doors, ceiling beams, and rafters, for example, can be reused after checking their technical condition. An example is the reuse of 80-90% of materials (doors, beams, wall cladding, among others) from demolishing the local government headquarters in Terneuzen, the Netherlands, in other construction projects.
  

  An essential aspect of reusing wood in construction is its preservation (protecting it from the harmful effects of weather, insects, or fungi), which can be hindered by using toxic preservatives posing a risk to human health during processing or preventing the joining of elements by undesirable reactions between preservatives and adhesives^[1].

  Properly storing wooden components is also essential to avoid any damage or deformation due to moisture.

• Recycling wooden elements: wooden elements such as furniture, pallets, and crates can be recycled into other furniture, flooring, ornaments, decorative elements, or garden structures. An example of such use is recycling bar stools and flooring from a nearby monastery into flooring in the Circl pavilion in Amsterdam, the Netherlands.
• Recycling wood waste: wood waste (e.g., sawdust or wood construction waste) can be used to produce, for example, insulation materials (such as wood wool), OSB-type particleboard or composite panels^[1], glulam^[6], or walls made from renewable materials produced using 3D printing technology^[7].