Bio-based building materials incorporate biomass, 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. [1] [2]
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. [3]
Building impacts belong to two distinct but interrelated types of carbon emissions: operational 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. [4] 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, [5] the embodied carbon associated with building materials has only recently gained significant attention. [6] [7] [8] This tendency has consequently resulted in a growing interest in the use of low-carbon bio-based materials. [9] [10] [11]
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. [12] 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. [13] During this time, carbon is stored in the building and its emissions are thus slowed down. [14]
Researchers proved that incorporating a larger share of bio-materials can reduce a building's embodied energy by about 20%. [15] Looking at the wider perspective, studies demonstrated that the use of bio-based materials in the built environment would have the potential to reduce over 320,000 tons of carbon dioxide emissions by 2050, which is set as target date by European Union to reach carbon neutrality. [16] Moreover, with buildings becoming more energy-efficient, the embodied impacts from producing and installing new materials contribute significantly to total lifecycle emissions, ranging from 10% to as much as 80% in highly efficient buildings. [17] This scenario highlights the potential for bio-based materials to have a substantial impact on reducing overall building energy emissions. [17]
Bio-based building materials can be classified depending on their natural origins and on their physical properties, which influence their behaviour when applied to the building system. [18] According to their chemical structure and to their characteristic of being renewable, bio-based materials can be divided into lignocellulosic materials, which come from forestry, vegetation, agriculture; protein-based materials, coming from farming, such as wool and feathers; [19] earth; [20] living materials made of micro-organisms such as mycelium and algae. [21]
Natural materials have been traditionally used in architecture since the vernacular period. [21] Presently, these materials stand out through innovative applications, [22] [23] [24] while novel bio-materials, such as living materials, and bio-wastes, enter the discussion intending to enhance circular business models.
Among bio-materials, timber, as part of a long, preindustrial history of buildings, [10] 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 the construction sector. [25] [26] 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) [27] and releases significant less GHGs into the atmosphere compared with mineral-based construction. [28] Moreover, wood is considered highly recyclable, as it enables several reuse options. [29]
However, it is important to consider that 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, timber construction can't be climate neutral. [30] Moreover, in the European context, studies have shown that there is an insufficient quantity of timber to meet the expected demand if there were to be a complete shift towards a timber-based built environment. [31]
Due to its strength, durability, non-combustibility, and ability to enhance indoor air quality, also rammed earth has been largely used in construction, starting from the 16th and 17th centuries. [32] With the advent of the Industrial Revolution, however, standardizing earthen materials became difficult, making it challenging to utilize them as effectively as concrete and bricks. [32]
Nowadays, because of low embodied carbon, availability, safety, and thermal characteristics of these building materials, they become a particularly attractive alternatives to more traditional ones. Moreover, there is the potentiality to circumvent disadvantages, such as on-site weather-dependency, by using prefabricated elements [33] [34] [35] and innovative manufacturing processes. [22] In this regard, the Austrian company Erden [36] has developed a technique to prefabricate rammed earth wall elements that can be stacked to construct large-scale buildings. The Belgian BC Materials, [37] instead, transforms excavated earth into building materials, with the production of earth blocks masonry, plasters and paints.
Moreover, the use of additive manufacturing enters the debate as a method with the potentiality to enhance the level of quality in detailing, accuracy, finishing, and reproducibility, while reducing labour needs and increasing in pace. [38] [39] In this regard, a recent collaboration between Mario Cucinella Architects [40] and Wasp, [41] an Italian company specialised in 3D printing, has resulted in the first 3D-printed, fully circular housing constructions made by earth, called TECLA. [22]
Unlike timber, fast-growing materials are bio-resources that have rapid growth, making them readily available for harvest and use in a very short period. [42] Fast-growing materials are typically derived from agricultural by-products, such as hemp, straw, flax, kenaf, and several species of reed, but can also include trees like bamboo and eucalyptus. [43] Due to their short crops rotation periods, these materials, when used, are directly compensated by the regrowth of the new plants and, overall, this results in a cooling effect on the atmosphere. [44]
Over last decades, various construction projects displayed their versatility by using them for many different applications, going from structural components crafted from bamboo to finishing materials like plaster, flooring, siding, roofing shingles, acoustic and thermal panels. [42]
Several studies document their applications in the built environment both as loose materials [45] [46] [47] and as part of a bio-mixture, such as flax concrete, [48] rice husks concrete, [49] straw fibers concrete, [50] or bamboo bio-concrete. [51] Among the others, hempcrete, made of lime and hemp shives, stands out due to its structural and insulating features, [23] [24] while enabling large carbon savings. [52] [53] [54]
In this context, several start-ups and innovative enterprises, such as RiceHouse, [55] Ecological Building System, [56] and Strawcture, [57] have already entered the market with competitive bio-composite alternatives, available either as loose materials or bound by natural or artificial binders.
Algae and mycelium are gaining interest as a research field for building applications. [58] [59] [60] [61] [62]
Algae are mainly discussed for their application on building facades for energy production through the development of bio-reactive façades. [63] [64] [65] The SolarLeaf pilot project, [62] implemented by Arup in Hamburg in 2013, marks the first real-world application of this technology in a residential context, showcasing its potential applicability to both new and existing buildings. [62]
Due to its ability to act as a natural binder instead, mycelium, the vegetative part of fungi, [66] is used as the binding agent of many composite materials. Over last years, the research on the topic has been exponential, due to the total biodegradability of the binder and to its ability to valorize waste material, by degrading them and using them as substrates for their growth. [67]
Different temporary projects have displayed the structural capacities of mycelium, both as monolithic and discrete separated elements. [68] Mycelium bricks were tested in 2014 with the construction of the Hi-fi tower, built at the Museum of Modern Art of New York by Arup and Living architecture. [21] Monolithic structures such as El Monolito Micelio [69] or the BioKnit pavilion, [70] were developed instead to grow mycelium either on-site or in a growing chamber in a single piece. [68]
The absence of established methods for producing large-scale mycelium-based composite components, primarily due to the low structural capabilities of such composites and various technological and design limitations, [68] represents today the main obstacle to its industrial scalability for building applications.
However, the Italian MOGU [71] and the American Ecovative [72] are two mycelium companies that were capable of scaling production to industrial levels, manufacturing and selling acoustic panels for indoor spaces. In this context, the project developed by the collaboration between Arup and the universities of Leuven (BE), Kassel (DE) and the Kalrsruher Institut für Technologie, named HOME, [60] aims to advance the upscaling of mycelium-based composites by developing prototypes and using diverse manufacturing processes for indoor acoustic insulation. [60]
Textile, papers and food wastes are also gaining progressive interest for buildings’ applications, as circular strategies enabling up-cycling processes and facilitating an effective transition toward a carbon-neutral society. [73]
Literature documents building components developed from food wastes coming from olive pruning, [74] almond skin wastes, [75] coffee beans and pea pods [76] for the realization of acoustic panels and thermal insulating panels.
In the same way, research has also focused on the reuse of cardboard and waste paper to enable the realisation of bio-composite panels. [77] [78] [79] In this regard, the thermal properties of cellulose fibers sourced from paper and cardboard waste have been tested and found to be particularly effective, achieving a thermal conductivity of 0.042 W·m−1·K−1, which is comparable to traditional materials. [80]
Due to the large waste generation caused by the fashion and clothing, [81] [82] several studies [82] [83] [84] and various research projects, such as the RECYdress project (2022) [85] and MATE.ria tessile (2023), [86] both conducted at Politecnico di Milano, have been developed to investigate textiles treatments and their use as secondary raw materials in the building sector. [86] Indeed, residual flows of textile are estimated to have a recycling potential of about 16 kWh of energy saved for each kilogram of textile. [84]
In this regard, the Waste Framework Directive, [87] which manages in Europe textile wastes obliging member states to ensure the separate collection of textiles for re-use and recycling, might be implemented in 2025 to promote extended producer responsibility schemes. [87] This would require fashion brands and textile producers to pay fees in order to help fund the textile waste collection and treatment costs. [88]
Several products leveraging recycled textiles for insulation are already available on the market. Inno-Therm, [89] a company from Great Britain, produces insulation from recycled industrial cotton material-denim. Similarly, Le Relais, [90] a French recycling company, which collects 45000 tons of used textiles annually, developed a thermal insulation product called Mettise. The product contains at least 85% recycled fibers and consists of cotton (70%), wool / acrylic (15%) and polyester (15%). [91]
To enable the wide utilization of bio-based materials in the built environment, there are several critical issues that require further investigation. [92] [93]
According to several researchers, one of the main issues of bio-based materials when applied to the construction sector is their required and expected performances, which shall be comparable to the ones of traditional engineered building materials. [93] [94] Extensive research is thus currently on-going to address the challenges allied with long-term durability, reliability, serviceability, properties and sustainable production. [93] [95]
In the European context, in the framework of meeting climate mitigation 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 through regulations such as The European Industrial Strategy, [96] the EU Biotechnology and Biomanufacturing Initiative [97] and the Circular Action Plan. [98]
However, as traditional materials still dominate the construction sector, there is a lack of understanding among some policymakers and developers regarding biomaterials. [34] According to Göswein, [92] the presence of a legal framework would reassure investors and insurance companies and enhance the promotion of circular economy dynamics.
Mycelium is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Its normal form is that of branched, slender, entangled, anastomosing, hyaline threads. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates into a monokaryotic mycelium, which cannot reproduce sexually; when two compatible monokaryotic mycelia join and form a dikaryotic mycelium, that mycelium may form fruiting bodies such as mushrooms. A mycelium may be minute, forming a colony that is too small to see, or may grow to span thousands of acres as in Armillaria.
Engineered wood, also called mass timber, composite wood, human-made wood, or manufactured board, includes a range of derivative wood products which are manufactured by binding or fixing the strands, particles, fibres, or veneers or boards of wood, together with adhesives, or other methods of fixation to form composite material. The panels vary in size but can range upwards of 64 by 8 feet and in the case of cross-laminated timber (CLT) can be of any thickness from a few inches to 16 inches (410 mm) or more. These products are engineered to precise design specifications, which are tested to meet national or international standards and provide uniformity and predictability in their structural performance. Engineered wood products are used in a variety of applications, from home construction to commercial buildings to industrial products. The products can be used for joists and beams that replace steel in many building projects. The term mass timber describes a group of building materials that can replace concrete assemblies.
A bio-based material is a material intentionally made, either wholly or partially, from substances derived from living organisms, such as plants, animals, enzymes, and microorganisms, including bacteria, fungi and yeast.
Asphalt concrete is a composite material commonly used to surface roads, parking lots, airports, and the core of embankment dams. Asphalt mixtures have been used in pavement construction since the beginning of the twentieth century. It consists of mineral aggregate bound together with bitumen, laid in layers, and compacted.
A phase-change material (PCM) is a substance which releases/absorbs sufficient energy at phase transition to provide useful heat or cooling. Generally the transition will be from one of the first two fundamental states of matter - solid and liquid - to the other. The phase transition may also be between non-classical states of matter, such as the conformity of crystals, where the material goes from conforming to one crystalline structure to conforming to another, which may be a higher or lower energy state.
Plastic recycling is the processing of plastic waste into other products. Recycling can reduce dependence on landfill, conserve resources and protect the environment from plastic pollution and greenhouse gas emissions. Recycling rates lag behind those of other recoverable materials, such as aluminium, glass and paper. From the start of plastic production through to 2015, the world produced around 6.3 billion tonnes of plastic waste, only 9% of which has been recycled and only ~1% has been recycled more than once. Of the remaining waste, 12% was incinerated and 79% was either sent to landfills or lost to the environment as pollution.
Bioplastics are plastic materials produced from renewable biomass sources, such as vegetable fats and oils, corn starch and rice starch, straw, woodchips, sawdust, recycled food waste, etc. Some bioplastics are obtained by processing directly from natural biopolymers including polysaccharides and proteins, while others are chemically synthesized from sugar derivatives and lipids from either plants or animals, or biologically generated by fermentation of sugars or lipids. In contrast, common plastics, such as fossil-fuel plastics are derived from petroleum or natural gas.
Sustainable architecture is architecture that seeks to minimize the negative environmental impact of buildings through improved efficiency and moderation in the use of materials, energy, development space and the ecosystem at large. Sustainable architecture uses a conscious approach to energy and ecological conservation in the design of the built environment.
Biochar is the lightweight black residue, consisting of carbon and ashes, remaining after the pyrolysis of biomass, and is a form of charcoal. Biochar is defined by the International Biochar Initiative as the "solid material obtained from the thermochemical conversion of biomass in an oxygen-limited environment".
Biotextiles are specialized materials engineered from natural or synthetic fibers. These textiles are designed to interact with biological systems, offering properties such as biocompatibility, porosity, and mechanical strength or are designed to be environmentally friendly for typical household applications. There are several uses for biotextiles since they are a broad category. The most common uses are for medical or household use. However, this term may also refer to textiles constructed from biological waste product. These biotextiles are not typically used for industrial purposes.
Biobased economy, bioeconomy or biotechonomy is economic activity involving the use of biotechnology and biomass in the production of goods, services, or energy. The terms are widely used by regional development agencies, national and international organizations, and biotechnology companies. They are closely linked to the evolution of the biotechnology industry and the capacity to study, understand, and manipulate genetic material that has been possible due to scientific research and technological development. This includes the application of scientific and technological developments to agriculture, health, chemical, and energy industries.
Hempcrete or hemplime is biocomposite material, a mixture of hemp hurds (shives) and lime, sand, or pozzolans, which is used as a material for construction and insulation. It is marketed under names like Hempcrete, Canobiote, Canosmose, Isochanvre and IsoHemp. Hempcrete is easier to work with than traditional lime mixes and acts as an insulator and moisture regulator. It lacks the brittleness of concrete and consequently does not need expansion joints.
Bioenergy with carbon capture and storage (BECCS) is the process of extracting bioenergy from biomass and capturing and storing as much as possible of the resulting CO2, thereby moving it from the biogenic carbon pool to the geological carbon pool. BECCS can theoretically be a "negative emissions technology" (NET), although its deployment at the scale considered by many governments and industries can "also pose major economic, technological, and social feasibility challenges; threaten food security and human rights; and risk overstepping multiple planetary boundaries, with potentially irreversible consequences". The carbon in the biomass comes from the greenhouse gas carbon dioxide (CO2) which is extracted from the atmosphere by the biomass when it grows. Energy ("bioenergy") is extracted in useful forms (electricity, heat, biofuels, etc.) as the biomass is utilized through combustion, fermentation, pyrolysis or other conversion methods.
A circular economy is a model of resource production and consumption in any economy that involves sharing, leasing, reusing, repairing, refurbishing, and recycling existing materials and products for as long as possible. The concept aims to tackle global challenges such as climate change, biodiversity loss, waste, and pollution by emphasizing the design-based implementation of the three base principles of the model. The main three principles required for the transformation to a circular economy are: designing out waste and pollution, keeping products and materials in use, and regenerating natural systems. CE is defined in contradistinction to the traditional linear economy.
The environmental impact of concrete, its manufacture, and its applications, are complex, driven in part by direct impacts of construction and infrastructure, as well as by CO2 emissions; between 4-8% of total global CO2 emissions come from concrete. Many depend on circumstances. A major component is cement, which has its own environmental and social impacts and contributes largely to those of concrete.
A living building material (LBM) is a material used in construction or industrial design that behaves in a way resembling a living organism. Examples include: self-mending biocement, self-replicating concrete replacement, and mycelium-based composites for construction and packaging. Artistic projects include building components and household items.
Textile-reinforced mortars (TRM) (also known as fabric-reinforced cementitious mortars are composite materials used in structural strengthening of existing buildings, most notably in seismic retrofitting. The material consists of bidirectional orthogonal textiles made from knitted, woven or simply stitched rovings of high-strength fibres, embedded in inorganic matrices. The textiles can also be made from natural fibres, e.g. hemp or flax.
Self-healing concrete is characterized as the capability of concrete to fix its cracks on its own autogenously or autonomously. It not only seals the cracks but also partially or entirely recovers the mechanical properties of the structural elements. This kind of concrete is also known as self-repairing concrete. Because concrete has a poor tensile strength compared to other building materials, it often develops cracks in the surface. These cracks reduce the durability of the concrete because they facilitate the flow of liquids and gases that may contain harmful compounds. If microcracks expand and reach the reinforcement, not only will the concrete itself be susceptible to attack, but so will the reinforcement steel bars. Therefore, it is essential to limit the crack's width and repair it as quickly as feasible. Self-healing concrete would not only make the material more sustainable, but it would also contribute to an increase in the service life of concrete structures and make the material more durable and environmentally friendly.
Mycelium, a root-like structure that comprises the main vegetative growth of fungi, has been identified as an ecologically friendly substitute to a litany of materials throughout different industries, including but not limited to packaging, fashion and building materials. Such substitutes present a biodegradable alternative to conventional materials.
Cork thermal insulation refers to the use of cork as a material to provide thermal insulation against heat transfer. Cork is suitable as thermal insulator, as it is characterized by lightness, elasticity, impermeability, and fire resistance. In construction, cork can be applied in various construction elements like floors, walls, roofs, and lofts to reduce the need for heating or cooling and enhance energy efficiency. Studies indicate that cork's thermal insulation performance remains unaffected by moisture absorption during rainy seasons, making it suitable for diverse climates. Additionally, research on cork-based composites, such as cork-gypsum structures, suggests a substantial improvement in energy efficiency for buildings.
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