Beyond the Usual Suspects: A Critical Review of Sustainable Materials in a Circular Economy

Abstract

The pursuit of sustainability in the built environment has driven increased interest in materials with reduced environmental impact. While materials like bamboo, reclaimed wood, and recycled steel have gained traction, a truly sustainable approach requires a more holistic perspective encompassing lifecycle assessment (LCA), circular economy principles, and innovative material development. This research report delves into the complexities of sustainable materials, moving beyond a simple comparison of environmental impacts to examine performance characteristics, economic viability, and the potential for closed-loop material flows. We critically evaluate established sustainable materials, explore emerging bio-based and mineral-based alternatives, and discuss the challenges and opportunities associated with their widespread adoption. Furthermore, we address the limitations of current LCA methodologies and advocate for a systems-thinking approach that considers the social and economic dimensions of material selection within a broader context of resource scarcity and climate change. Our analysis emphasizes the need for interdisciplinary collaboration, policy support, and technological innovation to accelerate the transition towards a genuinely sustainable materials economy.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

1. Introduction

The construction industry is a significant contributor to global greenhouse gas emissions, resource depletion, and waste generation. Concrete and steel production alone account for a substantial portion of industrial CO2 emissions [1]. The extraction, processing, manufacturing, transportation, and disposal of building materials all contribute to a substantial environmental footprint. Therefore, the selection of sustainable materials is paramount in mitigating the adverse impacts of the built environment.

The term “sustainable material” is often used loosely, and its definition can be subjective. A truly sustainable material should not only have a low environmental impact but also be durable, perform adequately for its intended application, and be economically viable. Ideally, a sustainable material should be part of a closed-loop system where it can be reused, recycled, or composted at the end of its life, minimizing waste and maximizing resource utilization. This aligns with the principles of a circular economy, which aims to decouple economic growth from resource consumption [2].

While materials like cellulose insulation, mineral wool, bamboo, cork, reclaimed wood, and recycled steel offer improvements over conventional materials in specific areas, a comprehensive understanding of their limitations and potential trade-offs is crucial. Furthermore, the focus on established sustainable materials can sometimes overshadow the potential of innovative and emerging alternatives. This research report aims to provide a critical and in-depth analysis of sustainable materials, encompassing their lifecycle environmental impacts, performance characteristics, economic feasibility, and their role in a circular economy.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

2. Lifecycle Assessment (LCA) and Environmental Impact

Lifecycle assessment (LCA) is a standardized methodology for evaluating the environmental impacts of a product or service throughout its entire lifecycle, from raw material extraction to end-of-life disposal [3]. LCA provides a framework for comparing the environmental performance of different materials and identifying opportunities for improvement. However, LCA also has its limitations, and its results should be interpreted with caution.

2.1. Methodological Considerations

The accuracy and reliability of LCA results depend heavily on the scope of the assessment, the data quality, and the assumptions made. Different LCA methodologies and software tools can yield different results, making it challenging to compare studies across different contexts. Key considerations include:

• System Boundary: Defining the system boundary is crucial as it determines which processes and impacts are included in the assessment. A “cradle-to-gate” assessment only considers the environmental impacts up to the point of manufacture, while a “cradle-to-grave” assessment includes the entire lifecycle, including end-of-life disposal. Cradle-to-cradle assesses reuse potential. An incomplete system boundary can lead to underestimation of the overall environmental impact.
• Data Quality: LCA relies on accurate and reliable data for material inputs, energy consumption, and emissions. Data gaps and uncertainties can significantly affect the results. Generic or average data can be used when specific data is unavailable, but this can reduce the accuracy of the assessment. Sourcing data from Environmental Product Declarations (EPDs) and peer-reviewed literature is crucial for enhancing data quality.
• Allocation Methods: When a process produces multiple products or by-products, allocation methods are used to assign environmental impacts to each product. Different allocation methods, such as mass allocation or economic allocation, can lead to different results.
• Impact Categories: LCA assesses a range of environmental impacts, including global warming potential (GWP), acidification potential, eutrophication potential, and resource depletion. Different impact categories may be weighted differently depending on the specific goals of the assessment. The choice of impact categories can influence the relative ranking of different materials.

2.2. Comparative LCA of Common Sustainable Materials

Numerous LCA studies have compared the environmental impacts of different building materials. Generally, materials with low embodied energy, high recycled content, and renewable sourcing tend to perform better in LCA studies. Below is a summary of common sustainable materials and their environmental footprint:

• Cellulose Insulation: Made from recycled paper, cellulose insulation has a low embodied energy and can sequester carbon. However, the production process can involve the use of boric acid as a fire retardant, which can have environmental impacts. Furthermore, the performance of cellulose insulation can be affected by moisture.
• Mineral Wool: Made from recycled glass, slag, or rock, mineral wool has good thermal performance and is fire-resistant. However, the manufacturing process can be energy-intensive, and some mineral wool products may contain formaldehyde as a binder. The environmental impact of mineral wool can vary depending on the raw materials used and the manufacturing process.
• Bamboo: A rapidly renewable resource, bamboo has a high strength-to-weight ratio and can sequester carbon. However, the processing and transportation of bamboo can contribute to its environmental footprint. The durability of bamboo can also be a concern in certain climates.
• Cork: Harvested from the bark of cork oak trees, cork is a renewable and biodegradable material. Cork is used for insulation, flooring, and other applications. The environmental impact of cork is generally low, but the transportation from cork-producing regions (e.g., Portugal) can contribute to its overall footprint.
• Reclaimed Wood: Reusing wood from demolition or deconstruction projects can significantly reduce the environmental impact compared to using virgin timber. Reclaimed wood can have a unique aesthetic appeal. However, the availability of reclaimed wood can be limited, and the quality and consistency can vary. Often, reclaimed wood requires significant cleaning and remanufacturing before it can be reused. The use of old growth timber is a key benefit.
• Recycled Steel: Steel produced from recycled scrap has a significantly lower environmental impact than steel produced from virgin iron ore. Recycling steel reduces energy consumption and greenhouse gas emissions. However, the quality of recycled steel can be affected by contaminants, and the recycling process can generate air and water pollution.

These results can vary drastically based on different manufacturing locations and local energy grids. Understanding where these materials originate and their method of production is key to selecting the most effective material. Additionally, the end of life scenario must be considered at the design phase to improve material recovery.

2.3. Limitations of LCA and the Need for a Systems-Thinking Approach

Despite its usefulness, LCA has limitations. It primarily focuses on environmental impacts and often overlooks social and economic considerations. LCA results can be highly sensitive to assumptions and data inputs, and it can be challenging to capture the full complexity of real-world systems. Furthermore, LCA often fails to adequately address issues such as biodiversity loss, social equity, and ethical sourcing [4].

A systems-thinking approach is needed to overcome the limitations of LCA. This approach considers the interconnectedness of environmental, social, and economic factors and emphasizes the importance of understanding the broader context in which materials are used. A systems-thinking approach encourages the evaluation of materials not only based on their environmental performance but also on their social and economic impacts, their contribution to a circular economy, and their potential to promote innovation and resilience [5].

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

3. Performance Characteristics and Suitability for Different Applications

In addition to environmental impact, the performance characteristics of a material are crucial in determining its suitability for specific applications. This section examines the performance characteristics of the materials mentioned in the abstract and considers their suitability for different use cases.

3.1. Thermal Properties and Insulation

Thermal performance is a key consideration for building materials, especially for insulation applications. Materials with low thermal conductivity provide better insulation, reducing energy consumption for heating and cooling.

• Cellulose Insulation: Cellulose insulation has good thermal performance, with an R-value (resistance to heat flow) of around 3.7 per inch. It also has good air sealing properties, which can further improve energy efficiency.
• Mineral Wool: Mineral wool also has good thermal performance, with an R-value of around 3.0 to 4.0 per inch. It is also fire-resistant and sound-absorbent.
• Cork: Cork has moderate thermal performance, with an R-value of around 3.5 per inch. It is also water-resistant and naturally resistant to mold and mildew.

When selecting insulation materials, it is important to consider the climate, the building design, and the desired level of thermal performance. Also, consider the effects of any chemical treatment that may be required to achieve fire resistance, and the effect this has on any recycling or disposal options.

3.2. Durability and Structural Performance

Durability and structural performance are critical for building materials used in structural elements, such as walls, floors, and roofs. Materials should be able to withstand environmental stresses, such as moisture, temperature fluctuations, and biological attack.

• Bamboo: Bamboo has a high strength-to-weight ratio and can be used in structural applications, particularly in regions where it is readily available. However, bamboo is susceptible to moisture and insect damage and requires proper treatment and maintenance.
• Reclaimed Wood: Reclaimed wood can be used in structural applications if it is properly graded and treated. The durability of reclaimed wood depends on the type of wood, its age, and its previous use. Species such as old growth redwood and douglas fir are highly desirable for use as structural elements. Some may be treated with chemicals that reduce its potential for reuse at the end of its service life.
• Recycled Steel: Recycled steel can be used in structural applications, such as framing and reinforcement. Recycled steel has similar strength and durability to virgin steel. The steel industry has a well-established recycling infrastructure, making recycled steel a readily available and sustainable option.

The choice of structural materials should be based on the specific requirements of the building design, the local climate, and the availability of materials. Appropriate material testing and engineering analysis are essential to ensure the structural integrity and durability of the building.

3.3. Fire Resistance

Fire resistance is a crucial safety consideration for building materials. Materials should be able to resist ignition and spread of fire, providing occupants with sufficient time to escape in case of a fire.

• Mineral Wool: Mineral wool is inherently fire-resistant and does not require any additional fire retardants. This makes it a safe and sustainable option for insulation.
• Cellulose Insulation: Cellulose insulation can be treated with fire retardants to improve its fire resistance. However, the use of fire retardants can have environmental impacts, and some fire retardants may release harmful chemicals when exposed to heat.
• Bamboo: Bamboo is not inherently fire-resistant and requires treatment with fire retardants to meet building code requirements. However, the use of fire retardants can affect the sustainability of bamboo.
• Reclaimed Wood: The fire resistance of reclaimed wood depends on the type of wood and its density. Dense hardwoods are generally more fire-resistant than softwoods.

Building codes and regulations specify the required fire resistance for different building elements. Materials should be selected and installed to meet these requirements.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

4. Innovative and Emerging Materials

Beyond the established sustainable materials, a number of innovative and emerging materials offer promising solutions for reducing the environmental impact of the built environment. These materials are often bio-based, mineral-based, or utilize waste materials.

4.1. Bio-Based Materials

Bio-based materials are derived from renewable biological resources, such as plants, algae, and fungi. These materials can sequester carbon and reduce the reliance on fossil fuels. Examples of bio-based materials include:

• Mycelium Composites: Mycelium is the vegetative part of a fungus, and it can be used to create composite materials by growing it on agricultural waste, such as hemp or straw. Mycelium composites are lightweight, strong, and biodegradable and can be used for insulation, packaging, and even structural elements. [6]
• Hempcrete: Hempcrete is a composite material made from hemp shives (the woody core of the hemp plant), lime, and water. Hempcrete is lightweight, breathable, and has good thermal performance. It can be used for walls, roofs, and floors.
• Bio-plastics: Bio-plastics are plastics made from renewable biological resources, such as corn starch or sugarcane. Bio-plastics can be used for a variety of applications, including packaging, textiles, and building materials. However, the biodegradability of bio-plastics can vary, and some bio-plastics require specific conditions to decompose.

4.2. Mineral-Based Materials

Mineral-based materials are derived from abundant minerals and can offer durable and fire-resistant solutions. Examples of mineral-based materials include:

• Ferrock: Ferrock is a cement-like material made from recycled steel dust and silica. Ferrock can sequester carbon dioxide during its production, making it a carbon-negative material.
• Magnesium Oxide Cement: Magnesium oxide cement (MOC) is a cement that uses magnesium oxide instead of traditional Portland cement. MOC has a lower carbon footprint than Portland cement and can be used for a variety of applications, including flooring, walls, and structural elements.
• Earth-Based Materials: Materials like rammed earth, adobe, and cob are used extensively around the world, particularly in arid areas. These are naturally sourced materials that have minimal processing, but care must be taken during the construction process to achieve the desired level of thermal and structural performance.

4.3. Materials Utilizing Waste

Utilizing waste materials in construction can reduce landfill waste and conserve virgin resources. Examples of materials utilizing waste include:

• Recycled Plastic Lumber: Recycled plastic lumber is made from recycled plastic bottles and other plastic waste. It can be used for decking, fencing, and other outdoor applications.
• Tyre-Derived Aggregate (TDA): TDA is made from shredded scrap tires and can be used as a lightweight fill material in construction. TDA can reduce the amount of waste sent to landfills and provide a cost-effective alternative to traditional fill materials. However, the use of TDA can raise concerns about the leaching of chemicals and the potential for fire hazards.
• Agricultural Waste: Rice husks, straw bales, and other agricultural waste products can be used as building materials. Rice husks can be used as insulation, and straw bales can be used for walls. However, the durability and fire resistance of agricultural waste materials can be a concern, and they may require treatment to improve their performance.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

5. Cost and Availability

The cost and availability of sustainable materials are important factors that can influence their adoption. While some sustainable materials may have a higher initial cost than conventional materials, they can offer long-term cost savings through reduced energy consumption, lower maintenance costs, and extended lifespans. The availability of sustainable materials can vary depending on the region and the specific material.

5.1. Cost Analysis

The cost of sustainable materials can vary significantly depending on the material, the supplier, and the location. Some sustainable materials, such as reclaimed wood and recycled steel, may be cheaper than their virgin counterparts due to lower processing costs. Other sustainable materials, such as mycelium composites and hempcrete, may have a higher initial cost due to limited production capacity and lack of established supply chains. However, as production scales up and supply chains become more established, the cost of these materials is likely to decrease.

A lifecycle cost analysis (LCCA) can be used to compare the total cost of ownership of different materials over their entire lifespan. LCCA considers not only the initial cost of the material but also the costs of installation, maintenance, energy consumption, and disposal. LCCA can help to identify the most cost-effective material over the long term.

5.2. Availability and Supply Chains

The availability of sustainable materials can vary depending on the region and the specific material. Some sustainable materials, such as recycled steel and reclaimed wood, are widely available in many regions. Other sustainable materials, such as mycelium composites and hempcrete, may have limited availability due to lack of established supply chains. The development of local supply chains for sustainable materials is crucial for increasing their availability and reducing transportation costs.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

6. Challenges and Opportunities

The widespread adoption of sustainable materials faces several challenges, including:

• Lack of Awareness and Education: Many architects, engineers, and builders are not fully aware of the benefits of sustainable materials or how to use them effectively. There is a need for more education and training on sustainable materials and their applications.
• Building Codes and Regulations: Building codes and regulations can sometimes hinder the adoption of sustainable materials. Some codes may not recognize or adequately address the unique properties of sustainable materials. There is a need for building codes and regulations to be updated to reflect the latest advances in sustainable materials.
• Lack of Standardization and Certification: The lack of standardization and certification for sustainable materials can make it difficult for specifiers to compare different products and ensure their quality. The development of industry standards and certification programs for sustainable materials is crucial for promoting their adoption.
• Resistance to Change: The construction industry is often resistant to change, and there can be a reluctance to adopt new materials and technologies. Overcoming this resistance requires strong leadership, effective communication, and successful demonstration projects.

Despite these challenges, there are also significant opportunities for the widespread adoption of sustainable materials:

• Growing Demand for Sustainable Buildings: The growing demand for sustainable buildings is driving increased interest in sustainable materials. As more clients and tenants demand green buildings, architects, engineers, and builders will be more likely to use sustainable materials.
• Government Incentives and Policies: Government incentives and policies can play a significant role in promoting the adoption of sustainable materials. Tax credits, grants, and building code incentives can make sustainable materials more cost-competitive and encourage their use.
• Technological Innovation: Technological innovation is driving the development of new and improved sustainable materials. New materials with enhanced performance, lower environmental impact, and reduced cost are constantly being developed. Research funding is crucial for creating new products and developing better methods for utilizing waste streams.
• Circular Economy Initiatives: The transition towards a circular economy is creating new opportunities for sustainable materials. As waste is increasingly seen as a resource, there is growing interest in materials that can be reused, recycled, or composted at the end of their life.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

7. Conclusion

The selection of sustainable materials is critical for reducing the environmental impact of the built environment. While materials like cellulose insulation, mineral wool, bamboo, cork, reclaimed wood, and recycled steel offer improvements over conventional materials, a truly sustainable approach requires a more holistic perspective encompassing lifecycle assessment, circular economy principles, and innovative material development.

This research report has highlighted the complexities of sustainable materials, examining their environmental impacts, performance characteristics, economic viability, and their role in a circular economy. We have critically evaluated established sustainable materials, explored emerging bio-based and mineral-based alternatives, and discussed the challenges and opportunities associated with their widespread adoption. Furthermore, we have emphasized the limitations of current LCA methodologies and advocated for a systems-thinking approach that considers the social and economic dimensions of material selection.

The transition towards a genuinely sustainable materials economy requires interdisciplinary collaboration, policy support, and technological innovation. Architects, engineers, builders, policymakers, and researchers must work together to develop and implement sustainable materials strategies that address the environmental, social, and economic challenges of the 21st century. By embracing a systems-thinking approach and investing in innovation, we can create a built environment that is both sustainable and resilient.

Many thanks to our sponsor Focus 360 Energy who helped us prepare this research report.

References

[1] World Green Building Council. (2019). Bringing Embodied Carbon Upfront: Coordinated action for the building and construction sector to tackle embodied carbon. https://www.worldgbc.org/bringing-embodied-carbon-upfront

[2] Ellen MacArthur Foundation. (2013). Towards the Circular Economy: Economic and business rationale for an accelerated transition. https://ellenmacarthurfoundation.org/

[3] ISO 14040:2006. Environmental management — Life cycle assessment — Principles and framework.

[4] Glavic, P., & Lukman, R. (2007). Review of sustainability terms and their definitions. Journal of Cleaner Production, 15(18), 1875-1885.

[5] Sterman, J. D. (2006). Learning from feedback in complex systems. System Dynamics Review, 12(2), 249-289.

[6] Holt, G. A., McIntyre, G., Flagg, D., Bayer, I. L., Wanjiru, A., Govenor, H. A., … & Currie, D. (2018). Fungal mycomaterials: a review of properties and applications. Frontiers in microbiology, 9, 2385.