Bio-based building materials

Bio-based materials in construction: new horizons to achieve a sustainable built environment

A building material is considered biobased when it incorporates biomass (Bourbia et al., 2023), which is derived from renewable materials of biological origin such as plants, (normally co-products from the agro-industrial and forestry sector), animals, enzymes, and microorganisms, including bacteria, fungi, and yeast. Today bio-based materials can represent a possible key-strategy to address the significant environmental impact of the construction sector, which accounts for around 40% of global carbon emissions.

Building impacts belong to two distinct but interrelated types of carbon emissions: operational carbon and embodied carbon. Operational carbon includes emissions related to the building's functioning, such as lighting and heating; embodied carbon encompasses emissions resulting from the physical construction of buildings, including the processing of materials, material waste, transportation, assembly, and disassembly. While research and policy over the past decades have primarily focused on reducing greenhouse gas (GHG) emissions during building operations, by enacting for instance the EU Energy Performance of Buildings Directive , the embodied carbon associated with building materials has only recently gained significant attention and thus bio-materials for construction applications. Studies indicate that the embodied impacts from producing and installing new materials can contribute significantly to total lifecycle emissions, ranging from 10% to as much as 80% in highly efficient buildings . Moreover, it has been proved that incorporating a larger share of bio-materials can reduce a building's embodied energy by about 20% . Indeed, bio-materials and their co-products offer various benefits: they are renewable, often locally available and during the plant’s growth carbon is sequestered , which enhances the production of possible alternative bio-components. This means that when bio-based construction materials are used as buildings’ components, their lifespan is usually defined by the building’s service life and results in a temporary reduction of the CO2 concentration in the atmosphere. During this time, carbon is stored in the building and its emissions are thus slowed down, which results in a temporary reduction of the CO2 concentration in the atmosphere.

Bio-based building materials can be classified depending on their natural origins and on their physical properties, which influence their application in the building system. According to their chemical properties, bio-based materials can be divided into lignocellulosic materials, which come from forestry, vegetation and from agriculture; protein-based materials, coming from farming, (feathers for instance); earth and soil; living matter such as mycelium and algae.

From traditional to innovative building applications

While a few bio-based materials have been historically used in the building sector for different purposes, others emerged only in recent years, to contribute to a more sustainable built environment. In this regard, bio-residues and post-consumer wastes also enter the topic, intending to enhance circular business models by reintroducing them for the production of new building components.

Earth and timber

Earth and timber have been historically used for construction purposes in all continents and with many different outcomes.

Rammed earth is known for its strength, durability, non-combustibility, and ability to enhance indoor air quality. Consequently, its use in construction can be traced back to the 16th and 17th centuries (Roger Boltshauser, Cyril Veillon, Nadja Maillard (eds.) Pisé. Rammed Earth). The advent of the Industrial Revolution and the consequent difficulties in standardising the earth made it hard to capitalise it in the same way as, for example, concrete and bricks. With time, thus, earth-building techniques have been forgotten (Roger Boltshauser, Cyril Veillon, Nadja Maillard (eds.) Pisé. Rammed Earth). However, today this building material, because of its low embodied carbon, affordability, safety, and thermal characteristics (Ben-Alon et al. 2019), becomes a particularly attractive alternative to more traditional ones, with the potential to circumvent disadvantages, such as on-site weather-dependency, by using prefabricated elements.

In recent years, indeed, there has been a growing interest in utilizing earth-based materials for construction purposes (Maierdan et al. 2021; 2022). The Austrian company Erden (https://www.erden.at/) has developed a technique to prefabricate rammed earth wall elements that can be stacked to construct large-scale buildings. The Belgian BC Materials (https://bcmaterials.org/), instead, transforms excavated earth into building materials, with the production of earth blocks masonry, plasters and paints. The use of additive manufacturing also enters the debate, as a method to potentially enhance the level of quality in detailing, accuracy, finishing, and reproducibility while reducing labour needs and increasing pace (Pajonk et al. 2022; Correa et al. 2015) . In this regard, a recent collaboration between Mario Cucinella Architects (https://www.mcarchitects.it/) and Wasp (https://www.3dwasp.com/en/), an Italian company specialising in 3D printing, has resulted in the first 3D-printed fully circular housing construction of earth, called TECLA.

Among bio-materials applications in the construction sector and differently from earth, timber has always received the main attention from policy and industry and, in recent years, it has been mainly advocated by researchers and policymakers to replace concrete, iron and steel in construction . Indeed, modular timber construction, such as Plywood, Laminated Veneer Lumber LVL, Panels, Cross Laminated Timber CLT, allows for storing a significant amount of carbon in the structure (50% of the mass) and releases significant less GHGs into the atmosphere compared with mineral-based construction. However, the climate benefit associated with biogenic carbon storage is only achieved when replaced by the growth of another tree, which normally takes decades. Therefore, even if still representing a renewable resource, within a short time horizon, such as 2050, as target date set by European Union for climate neutrality, timber construction can't be climate neutral . Moreover, sufficient resources have been proved not being readily available to meet the expected demand in case of a complete shift towards a timber-based built environment. Given the above, relying on the intensified use of timber for construction because of future climate mitigation and reduced Green House Gas emissions (GHG) can be a possibility only if a sustainable forest management and a critical perspective in terms of construction application are guaranteed.

Fast-growing bio-materials

Fast-growing materials are bio-resources that have rapid growth, making them readily available for harvest and use in a very short period. Recently, they have gained significant attention for their potential wide range of applications in the construction sector, both as aggregates, in conjunction to a binder, and as loose materials. Unlike timber, these types of bio-materials, typically derived from agricultural by-products such as hemp, straw, flax, kenaf, and several species of reed, but also including trees like bamboo and eucalyptus, are characterized by very short crop rotation periods. This means that carbon emission due to the production of building material is directly compensated by the regrowth of the new plant and, overall, this results in a cooling effect on the atmosphere

Over last decades, various construction projects displayed their versatility by using them for many different construction applications, going from structural components crafted from bamboo to finishing materials like plaster, flooring, siding, roofing shingles, and acoustic panels . Among fast-growing materials coming from agricultural by-products, straw and hemp were the first ones to be researched and tested for buildings applications , due to their good thermal properties and to their large availability all around the world. More specifically, while straw has been proven to have a thermal conductivity comparable to traditional materials (0.04 mK) (Costes et al. 2017; Dessuky 2009), hemp has shown notable thermal resistance, mechanical and acoustic features. Among different hemp composites, hempcrete has particularly gained attention as a bio-mixture made of a binder and hemp shives, with structural and insulating features (Benmahiddine et al. 2020; Bennai et al. 2018). CHECK THE REFERENCES After being primarily employed to build non-weight bearing in-fill walls in France, CHECK REFERENCES, nowadays its thermal (Benmahiddine et al. 2021; Rahim et al. 2015) and acoustic (Kinnane et al. 2016) properties make it a competitive alternative to classic building materials, while enabling large carbon savings. Similarly, in Brazil, the implementation of bio-concrete solutions using bamboo had the potential to reduce up to 65% of carbon emissions [Correa de Melo, P.; Rosse Caldas, L.; Masera, G.; Pittau, F. The potential of carbon storage in bio-based solutions to mitigate the climate impact of social housing development in Brazil. J. Clean. Prod. 2023, 433, 139862. [Google Scholar] [CrossRef]].

PICTURE OF HEMPCRETE Several start-ups and innovative enterprises, such as RiceHouse (https://www.ricehouse.it/), Ecological Building System (https://www.ecologicalbuildingsystems.com/) and Strawcture (https://strawcture.com/), have already entered the market with competitive bio-composite alternatives made of fast-growing materials, either in the form of loose material or bond either other natural or artificial binders for diverse building applications. Their contribution enables the connection between different stakeholders and the creation of circular businesses dynamics, which integrates residues recovery for the production of new building component.

Living building materials: mycelium and algae

Among innovative bio-materials, algae and mycelium have a predominant position for building applications (Alemu et al., 2022; Kelsey Simpkins, 2022; Jones et al., 2018, 2020a, 2020b; Montjoy, 2022; Sarmadi & Mahdavinejad, 2023; Talaei et al., 2020;). Algae are mainly discussed for their application on building facades for energy production through the development of bioreactive façades (Ahmadi et al., 2023; Pruvost et al. 2016; Talaei et al., 2022), which generates renewable energy from algal biomass and solar thermal heat. The pilot project developed by Arup in Hamburg in 2013 and called SolarLeaf represents its first building application on a residential building and the realization of an integrated façade system that might be suitable potentially for both new and existing buildings.

Due to its ability to act as a natural binder, mycelium, the roots of fungi, instead is used as the binding agent of many composite materials, which are thus called myco-composites. Over last years, the research on the topic has been exponential, due to the total biodegradability of the binder, which might enable the production of totally natural composites, and to its good mechanical properties. CHECK. In this regard, different temporary projects have displayed the structural capacities of mycelium, both as monolithic and discrete separated elements. Mycelium bricks have been tested to on a real-life scale project for a temporary pavilion at the Museum of Modern Art of New York, while monolithic structures such as El Monolito Micelio (Dessi-Olive, 2019) or the BioKnit pavilion (Kaiser et al., 2023), have been developed to either grown directly on site or in a growing chamber in a single piece.

Despite there remains a lack of established methods to produce large-scale MBC components, due to both the low structural capabilities of such composites and technological and design limitations, (Rossi et al., 2022), the Italian company MOGU is one of the very few mycelium companies that were able to scale mycelium production to industrial levels, by producing and selling acoustic panels for indoor spaces. In this regard, the Arup project HOME has the exact purpose to trying upscaling mycelium based composites by developing prototype with diverse manufacturing processes for indoor acoustic insulation.

Post-consumer bio-wastes: closing the loop

Textile, papers and food wastes are also gaining progressive interest for buildings’ applications, as circular strategies promoting at the same time circular economies able to generate both up-cycling processes and an effective transition toward a carbon-neutral society (Aruta et al. 2021).

Many studies have recorded the utilization of food wastes for the development of building components, such as insulating panels, mortars, plasters and bricks [9–13]. Martellotta et al. [10], for instance, proposed the recovery olive pruning fibers for the production of sound absorption panels. Liuzzi et al. [11] carried out a study on almond skin waste for the creation of building thermal insulating panels. Schiavone et al. [13] proposed a review of acoustic and thermal insulating panels made of coffee beans or fava bean residues. In the same way, research has also focused on the reuse of cardboard and waste paper for the production of insulating panels. Mandili et al. [17] mixed it with lime, Bryski et al. [20] examined the properties of cellulose fibers sourced from paper and cardboard waste, obtaining a thermal conductivity of 0.042 W·m−1·K−1., which is comparable to traditional materials.

Fashion & clothing is one of the most important sectors of the global economy (Briga-Sá et al. 2022) and one of the main contributors to waste generation and fossil GHG emission (Aruta et al. 2023). Different papers have already focused on textiles possible features as building insulation (Aruta et al. 2023; Briga-Sá et al. 2022; Rubino et al. 2021; Muthu et al. 2012a; Muthu et al. 2012b), many studies on the topic are on their way (just in Politecnico, RECYdress project of 2022 and MATE.ria tessile of 2023) and a few products are already on the market, such as the ones produced by VRK isolatie ((https://materialdistrict.com/material/metisse-recycled-textile-insulation/ ). Indeed, residual flows of textile are estimated to have a recycling potential of about 16 kWh of energy saved for each kilogram of textile (Muthu et al. 2012a). Moreover, the Waste Framework Directive, which imposes the mandatory separate collection of textile waste in all Member States by 2025, preventing landfill (currently 57% of the total waste), incineration (25%), or export of textile wastes to non-European countries (Aruta et al. 2023), makes the topic even more crucial. However, materials’ separation is still considered its main challenging aspect, hindering the extensive reuse of obsolete textile.

Between opportunities and future challenges

Even though bio-based building materials, as above illustrated, might represent an impacting strategy to lower building emissions of the built environment, some relevant aspects need to be tackled to enable their further diffusion at an industrial scale.

The need for a policy framework

Even though, in the context of meeting climate mitigation objectives objectives before 2050, European Union is trying to implement, among other measures, the production and utilization of bio-based materials in many diverse sectors and segments of society by means of regulations such as the European Industrial Scale, the EU Biotechnology and Biomanufacturing Initiative and the Circular Action Plan, there is the need in the construction sector of a clear policy a to facilitate the use of biogenic materials for construction. A legal framework would reassure investors and insurance companies and enhance the promotion of circular economy dynamics, especially when coming to the use of agricultural waste products for secondary applications. (Göswein et al., 2022). The past has already witnessed to cases where the haste to deliver green societal transitions without an appropriate legal framework lead to important societal and economical failures. It’s the case of Brazil, where the development of the first generation of biofuels made with cereals and sugar crops caused a food crisis since crops were reallocated for energy production (Gasparatos et al. 2016).

Performance and standardisation

Even though bio materials in the built environment might represent, in terms of materials properties, a real alternative to traditional materials for the production of net-zero carbon building components, one of theit main issues regards durability, standardization and industrial scalability of the production. In this regard, materials complexity and composition, if might be able to provide building materials comparable to traditional ones, could imply significant energy consumption while limiting materials reversibility and separability.

Leuven typical bricks residential architecture

See also

• Mycelium-based materials

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Further reading

• McDonough, William (2002). From Cradle to Cradle. ISBN 0099535475.

External links

• Parkes, James. "The Dezeen guide to bio-based materials in architecture, design and interiors". Dezeen.
• Franco, José Tomás (February 18, 2021). "Round Houses of Raw Earth: 3D Printing Sustainable Homes in 200 Hours". archdaily.com.