BIM-integrated life cycle assessment of decentralized cement-based waste recycling in renovation projects – Nature

Executive Summary

This report details an investigation into decentralized community recycling of 100% cement-based waste (CBW) as a sustainable construction practice aligned with the United Nations Sustainable Development Goals (SDGs). Utilizing an integrated Building Information Modelling-Life Cycle Assessment (BIM-LCA) framework, the study evaluates the environmental and mechanical performance of recycled concrete aggregate (RCA) as a substitute for natural aggregates in non-structural concrete. This approach directly supports SDG 9 (Industry, Innovation, and Infrastructure), SDG 11 (Sustainable Cities and Communities), SDG 12 (Responsible Consumption and Production), and SDG 13 (Climate Action). A cradle-to-site LCA (A1-A4) revealed that the optimized recycled concrete mix (CBW2) achieved a 29% reduction in overall environmental impacts compared to conventional concrete. This demonstrates that decentralized recycling offers a viable pathway to enhance resource circularity, reduce carbon emissions, and build resilient urban infrastructure, thereby advancing key sustainability targets.

Introduction: Aligning Construction with Sustainable Development Goals

The global construction sector presents a significant challenge to achieving the Sustainable Development Goals, accounting for 36% of energy consumption and 39% of greenhouse gas (GHG) emissions. This intensive resource use, particularly of concrete, undermines progress toward SDG 12 (Responsible Consumption and Production) and SDG 13 (Climate Action). Simultaneously, the generation of nearly 10 billion metric tons of construction and demolition waste (CDW) annually, with a large portion sent to landfills, places immense pressure on urban environments, conflicting with the objectives of SDG 11 (Sustainable Cities and Communities). This report examines the potential of converting concrete waste (CW), a major component of CDW, into recycled concrete aggregate (RCA). By promoting a circular economy model, this practice reduces the demand for virgin natural aggregates, minimizes landfill waste, and lowers the carbon footprint of construction materials. The integration of digital technologies like BIM with LCA provides an innovative framework, consistent with SDG 9 (Industry, Innovation, and Infrastructure), to systematically assess and optimize the environmental performance of recycled materials, paving the way for more sustainable and resilient infrastructure.

Methodology: An Integrated Framework for Sustainable Assessment

A five-stage decision support system was developed to evaluate the use of CBW in alignment with circular economy principles and the SDGs. This methodology integrates material testing with advanced digital assessment tools to provide a holistic view of sustainability performance.

1. Quantification of CBW through 3D BIM modelling.
2. Analysis of physical, fresh-state, and mechanical properties of recycled aggregate concrete.
3. Execution of an attributional Life Cycle Assessment (LCA) for various recycling scenarios.
4. Estimation of environmental savings to quantify contributions toward SDG 12 and SDG 13.
5. Decision support based on the scenario with the lowest environmental impact.

BIM-LCA Integration for SDG Alignment

The integration of BIM and LCA is a critical innovation for advancing SDG 9 by digitalizing sustainability assessments in the built environment. This semi-automated approach enables the efficient extraction of material quantities and specifications from a digital model, which are then linked to environmental impact data from LCA databases. This process streamlines the calculation of embodied carbon and other environmental indicators, facilitating rapid and accurate evaluations that support low-carbon design decisions. By automating data exchange, the BIM-LCA framework reduces manual effort by over 90% while maintaining high accuracy, thereby empowering stakeholders to optimize resource efficiency and minimize waste in line with SDG 12.

Case Study: Promoting Sustainable Infrastructure in Aswan, Egypt (SDG 9, SDG 11)

The study was contextualized within Aswan, Egypt, a city facing challenges with CDW management. A local government-led decentralized recycling plant was proposed to process CBW from renovation projects, such as the AASTMT education building selected for this case study. This initiative directly addresses SDG 11.6 (reduce the adverse per capita environmental impact of cities, including by paying special attention to air quality and municipal and other waste management). By establishing local recycling infrastructure, the model promotes a circular economy at the community level, reduces transportation-related emissions, and creates value from waste, contributing to resilient and sustainable urban development as envisioned by SDG 9 and SDG 11.

Experimental Program: Material Innovation for Responsible Production (SDG 12)

An experimental program was conducted to validate the performance of recycled aggregate concrete (RAC) and ensure its suitability for non-structural applications. This aligns with SDG 12.5 (substantially reduce waste generation through prevention, reduction, recycling, and reuse). Three concrete mixes were tested:

• CBW0: A control mix with 100% natural aggregates (NA).
• CBW1: A recycled mix with 100% coarse RCA, 50% fine RCA, and a Styrene Butadiene Rubber (SBR) to water ratio of 1:25.
• CBW2: A recycled mix with 100% coarse RCA, 50% fine RCA, and an SBR/W ratio of 1:50.

Tests were performed to assess aggregate properties, fresh concrete workability, and hardened concrete mechanical properties (compressive and tensile strength), ensuring that the recycled material meets performance standards for sustainable product development.

Environmental Life Cycle Assessment (LCA)

A comparative cradle-to-site (A1-A4) LCA was conducted to quantify the environmental benefits of the recycling scenarios, directly supporting SDG 13 (Climate Action). The functional unit was defined as 1 m³ of concrete with comparable mechanical performance. The system boundary included:

• A1: Raw material supply (including RCA production).
• A2: Transportation of materials to the plant.
• A3: Concrete production.
• A4: Transportation of concrete to the construction site.

The assessment utilized SimaPro software with the Ecoinvent database and the EN 15804+A2 method to evaluate impact categories such as climate change (embodied carbon), water use, and resource depletion.

Results and Discussion: Quantifying Sustainability Impacts

Material Performance and Viability

The experimental results confirmed the viability of using high volumes of RCA in non-structural concrete. The CBW2 mix achieved a 28-day compressive strength of 16 MPa, meeting the 15 MPa minimum requirement for non-structural applications. While the inclusion of RCA reduced workability, the use of SBR as an admixture helped maintain adequate performance. These findings demonstrate that through innovative mix design, recycled materials can effectively replace virgin resources without compromising necessary performance, a key tenet of SDG 12.

Environmental Impact Assessment and Climate Action (SDG 13)

The LCA results revealed significant environmental benefits from using recycled materials and decentralized processing. Key findings include:

• Overall Impact Reduction: The CBW2 mix reduced total environmental impacts by 29% compared to the conventional concrete mix (CBW0).
• Climate Change Mitigation: CBW2 achieved a 15.2% reduction in climate change impact (embodied carbon) over the A1-A4 lifecycle stages. This directly contributes to SDG 13 by lowering the carbon footprint of construction materials.
• Resource Conservation: The gate-to-gate (A1-A2) analysis showed that RCA has over 95% lower GHG emissions and embodied carbon compared to NA, highlighting its crucial role in promoting SDG 12.
• Decentralization Benefits: The decentralized recycling model led to a 75% reduction in GHG emissions during the transportation phase (A4), underscoring its importance for building sustainable supply chains within cities (SDG 11).

Automation of BIM-LCA for Non-Structural Concrete Elements

The integrated BIM-LCA framework was applied to calculate the total embodied carbon for the ground floor elements of the case study building. The automated calculation showed that using the CBW2 mix would reduce the embodied carbon of these elements by 15.2% (from 33.3 tons to 28.3 tons). This demonstrates the power of digital tools (SDG 9) to provide rapid and reliable data for making informed, sustainable design choices that advance climate goals (SDG 13).

Conclusion: Advancing Sustainable Construction Practices

This study provides a robust, evidence-based framework for integrating decentralized CBW recycling into construction renovation projects, offering a scalable solution to advance multiple SDGs. The key conclusions are:

• The optimized recycled mix (CBW2) successfully balanced mechanical performance for non-structural applications with a significant 29% reduction in overall environmental impact, supporting SDG 12.
• Decentralized recycling facilities drastically cut transportation-related emissions by up to 75%, contributing to more sustainable urban logistics and resilient communities under SDG 11.
• The use of RCA offers a substantial climate benefit, with a 15.2% reduction in embodied carbon, directly addressing the call for SDG 13 (Climate Action).
• The semi-automated BIM-LCA framework proved to be an effective tool for rapid and accurate environmental assessment, promoting the type of innovation and sustainable infrastructure envisioned in SDG 9.

By combining material innovation, localized circular economy models, and digital technologies, this approach provides a strategic pathway for the construction industry to reduce its environmental footprint and contribute meaningfully to global sustainability targets.

Limitations and Future Recommendations for Achieving SDGs

While this research demonstrates a promising pathway, its broader implementation requires addressing several limitations to fully realize its potential contribution to the SDGs.

Limitations

• Technological and Financial Barriers: The adoption of BIM-LCA integration may be limited for small and medium-sized enterprises due to high initial costs and technical complexity, potentially hindering widespread progress on SDG 9.
• Long-Term Durability: The study focused on immediate mechanical and environmental performance. Further research is needed on the long-term durability of RAC to ensure the creation of resilient and long-lasting infrastructure (SDG 9, SDG 11).
• Contextual Feasibility: The success of decentralized recycling plants depends on local regulatory support, economic viability, and logistical frameworks, which may vary significantly across different urban contexts.

Recommendations for Future Research

• Enhance Accessibility of Digital Tools: Develop cost-effective, open-source BIM-LCA solutions to democratize access to sustainability assessment tools, thereby accelerating the industry’s capacity for innovation under SDG 9.
• Conduct Holistic Sustainability Assessments: Future studies should integrate economic (life cycle costing) and social (job creation, community impact) analyses to provide a comprehensive assessment across all three pillars of sustainable development.
• Expand Geographic and Contextual Applications: Replicate the study in diverse geographic and climatic regions to validate the framework’s adaptability and refine best practices for implementing circular economy models in construction globally.

Analysis of Sustainable Development Goals (SDGs) in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The article on decentralized recycling of cement-based waste (CBW) addresses several interconnected Sustainable Development Goals (SDGs) by focusing on sustainable construction practices, resource efficiency, waste management, and climate action. The following SDGs are most relevant:

• SDG 9: Industry, Innovation and Infrastructure

  This goal is addressed through the article’s focus on upgrading the construction industry with sustainable and innovative practices. The study proposes a new framework (integrated BIM-LCA) and a novel approach (decentralized community recycling) to improve resource efficiency and reduce the environmental footprint of construction activities. It promotes building resilient infrastructure by using recycled materials that meet performance standards for non-structural applications.

• SDG 11: Sustainable Cities and Communities

  The article directly connects to making cities more sustainable by tackling the massive issue of construction and demolition waste (CDW). It states that “construction, renovation, and demolition activities generate nearly 10 billion metric tons of waste globally, with an estimated 35% ending up in landfills.” By proposing a decentralized recycling model within urban districts (specifically in Aswan, Egypt), the study offers a practical solution to reduce the environmental impact of cities, manage waste locally, and promote a circular economy at the community level.

• SDG 12: Responsible Consumption and Production

  This is a central theme of the article. The research promotes sustainable consumption and production patterns by advocating for the recycling and reuse of cement-based waste. It focuses on replacing the consumption of virgin natural resources (natural aggregates) with recycled materials (recycled concrete aggregates – RCA). The entire study is a demonstration of how to “substantially reduce waste generation through prevention, reduction, recycling and reuse,” which is a core principle of SDG 12.

• SDG 13: Climate Action

  The article contributes to climate action by quantifying and demonstrating a reduction in greenhouse gas (GHG) emissions. The Life Cycle Assessment (LCA) measures the carbon footprint (embodied carbon – EC) of different concrete mixes. The findings show that using recycled aggregates leads to significant environmental savings, including a “15.2% reduction in EC compared to the baseline” and “over 95% lower GHGs and EC impacts” for RCA compared to natural aggregates on a gate-to-gate basis. This directly supports efforts to mitigate climate change by reducing emissions from the high-impact construction sector.

2. What specific targets under those SDGs can be identified based on the article’s content?

Based on the article’s focus on recycling, resource efficiency, and environmental impact reduction, several specific SDG targets can be identified:

1. Target 9.4: Upgrade infrastructure and retrofit industries for sustainability

   The article supports this target by proposing a method to make the construction industry more sustainable. It introduces an “integrated BIM-Life Cycle Assessment (LCA) framework” as an innovative and environmentally sound technology to evaluate and optimize the use of recycled materials. This framework helps upgrade industrial processes for concrete production with “increased resource-use efficiency.”

2. Target 11.6: Reduce the adverse environmental impact of cities

   This target aims to reduce the negative environmental effects of cities, with a special focus on waste management. The article’s proposal for “decentralized community recycling as a sustainable alternative to centralized recycling plants” directly addresses municipal and construction waste management. The case study in Aswan, Egypt, where “most of the CDW, including CW, are sent to landfills,” exemplifies how this approach can reduce urban environmental burdens.

3. Target 12.2: Achieve the sustainable management and efficient use of natural resources

   The study’s primary objective is to find a “viable alternative to centralized recycling facilities and landfilling” by using “recycled concrete aggregate as a substitute for natural aggregates.” This directly promotes the efficient use of natural resources by reducing the demand for quarrying new aggregates, which are, after water, the most consumed resource globally.

4. Target 12.5: Substantially reduce waste generation through recycling and reuse

   The research is fundamentally aligned with this target. It explores a pathway for “managing 100% cement-based waste (CBW) from renovation activities.” By demonstrating that recycled concrete can achieve the necessary mechanical performance for non-structural applications, the study provides a clear strategy for reducing waste generation by turning a waste stream into a valuable resource, thereby promoting a circular economy.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article provides several quantitative and qualitative indicators that can be used to measure progress towards the identified SDG targets. These are primarily derived from the Life Cycle Assessment (LCA) and the experimental results.

• Reduction in Greenhouse Gas (GHG) Emissions / Embodied Carbon (EC)

  This is a key indicator for Targets 9.4 and 13.2. The article quantifies this precisely, stating that the CBW2 mix achieved a “15.2% reduction in EC compared to the baseline CBW0” and that decentralized recycling led to “up to 75% lower GHGs” in transportation phases. The comparison showing RCA has “over 95% lower GHGs and EC impacts compared to NA” also serves as a powerful indicator.

• Percentage of Waste Recycled or Reused

  This indicator measures progress towards Targets 11.6 and 12.5. The study is designed around managing “100% cement-based waste” and investigates concrete mixes that incorporate “100% coarse RCA + 50% fine RCA.” This replacement percentage is a direct indicator of the recycling rate and the reduction of waste sent to landfills.

• Reduction in Natural Resource Consumption

  This indicator is relevant to Target 12.2. The substitution of natural aggregates (NA) with recycled concrete aggregates (RCA) is a direct measure of this. The article also highlights a significant reduction in another natural resource: water. It notes that “water use was the most strongly affected… with declines of 62.8%, and 66.4% for CBW1 and CBW2, respectively.”

• Overall Environmental Impact Reduction

  The LCA provides a broad indicator of environmental performance. The article concludes that the CBW2 mix reduced “overall environmental impacts by 29%” compared to conventional concrete. This composite indicator, covering various impact categories like ozone depletion and aquatic eutrophication, measures progress towards the broader goal of environmental sustainability in construction (Targets 9.4 and 11.6).

4. Table of SDGs, Targets, and Indicators

Source: nature.com