Framework for Dynamic Circular Economy in the Building Industry: Integration of Blockchain Technology and Multi-Criteria Decision-Making Approach

Abstract

The building industry is one of the most resource-intensive sectors in industrialized countries, requiring a shift from a linear to a more sustainable circular economic model. Nevertheless, there are several major challenges, such as the management of information regarding used materials and products, the lack of cross-sector documentation tools, and sales operations for implementing a dynamic circular economy in the building industry. To overcome these challenges, blockchain technology for documentation, tracing used materials and products, and the use of multi-criteria decision-making approaches for the ranking and selection of optimal used materials and products have emerged as crucial facilitators, with the potential to address the technological, organizational, environmental, and economic requirements. The purpose of this study is to develop a theoretical framework of a digital platform ecosystem for implementing a dynamic circular economy in the building industry through the integration of blockchain technology and a multi-criteria decision-making approach built upon their synergy. The priority order of two alternatives of used materials and products was determined according to the AHP method, leading to selection of the most sustainable alternative. This research study contributes to dynamic circular economies by (1) facilitating cross-sector information transparency and the tracing of used materials and products from their sources to their end-of-life stages and through (2) the ranking and selection of used materials and products based on their overall properties.

1. Introduction

The construction industry is the most considerable waste stream in industrialized countries [1]; by utilizing half of the materials consumed in Europe, generating 36% of the European Union’s total amount of waste and producing 39% of the world’s greenhouse gas emissions related to energy, the housing and infrastructure sectors significantly contribute to environmental issues. These sectors are responsible for approximately 15–30% of the overall environmental impact resulting from European consumption [1]. Limited material resources and large emissions of greenhouse gases from activities within the building industry have led to demands from society for sustainable development. The idea of a circular economy (CE) is gaining ground in the construction industry, hailed as a competent approach to deploying resource-efficient tools, techniques, and processes in order to reduce resource consumption and waste generation [2,3]. Waste management is an especially pressing concern within the construction sector. To put it into perspective, construction activities consume 30% of the world’s raw materials, occupy 12% of its available land, utilize 25% of global water resources, and consume 40% of the total energy produced globally. Shockingly, this industry produces an astonishing 3 billion tons of construction and demolition waste every year [4], significantly contributing to environmental harm because of the sheer volume of waste produced and its insufficient recycling rates [5].

Embracing a CE approach in the building industry represents a shift away from the predominantly linear economy, aiming to promote sustainable development and confirm the obtainability of resources for present and forthcoming peers. This transition involves reducing the consumption of resources and minimizing waste, emissions, and energy losses associated with building materials and products over time, all of which can be accomplished due to the implementation of various resource strategies [6]. In the building industry, the idea of a CE revolves around the concept of reverse logistics for construction products and materials [4]. In the realm of construction, reverse logistics pertains to a fusion of techniques and instruments designed for repurposing, reclaiming, and reconstituting building materials that have reached the conclusion of their useful lives, typically due to demolition and deconstruction processes [7,8]. Iacovidou and Purnell [9] illustrated that by repurposing building materials and products from existing physical infrastructure, we not only save resources but also foster the emergence of novel business models while generating environmental, technical, and social value. The Buildings as Material Bank (BAMB) project [10], which was formed by a multistakeholder consortium, has been at the forefront of creating and experimenting with circular methods and instruments intended to recover value from structures. Additional examples of trailblazers in this endeavor include Rotor [11,12] and Baubüro in situ [13]. Mhatre et al. [14] identified six CE adoption barriers in the built environment: economic, environmental, technical, societal, government, and behavioral. However, for the implementation of a feasible CE in the building industry, the absence of tools that facilitate communication and coordination across different sectors as well as increased access for used building materials and products needs to be addressed [15]. Digitalization and new technologies offer some of the necessary tools with which to address these challenges [6].

The building industry is the most considerable waste stream and is defined as a priority area in the EU’s CE Action Plan. Nevertheless, the building industry’s waste stream is commonly downcycled due to the lack of a framework and an integrated platform. Still, there are only a limited number of studies concerning the integration of a CE in a comprehensible manner. Recently, in a statement made in the ‘Europe’s Digital Decade’ program, digital transformation has been designated as one of the key focal points alongside the transition to a CE. Fueled by these ambitions, the development of frameworks that would increase CE transition is a necessity.

Blockchain technology (BCT) has garnered increasing attention due to its digitally distributed, decentralized, and exceptionally secure method of documenting dealings and monitoring assets within an enterprise system [16]. Its diverse applications in the construction industry encompass enhancing contractual procedures and building operations [17], facilitating risk and reward sharing amongst project stakeholders in integrated project delivery (IPD) [18], the automation of payments in construction in conjunction with employing the technology of robotic reality capture, and enhancing the ability to track prefabricated components at various levels of the building supply chain [19]. However, limited research has been conducted so far concerning the value of BCT in the CE transition. From a CE perspective, BCT is an enabling technology, particularly with respect to improving the efficiency and transparency of building information management (BIM) and information sharing for maintaining the value of resources throughout their lifecycles. BIM has played a pivotal role in the digital transformation of the construction sector, uniting a fragmented industry within a standardized digital platform. Considering BIM’s extensive adoption and adaptability, one could contend that it holds significant potential in the context of a CE, particularly concerning the construction, operation, and eventual dismantling of built assets in the future [20]. BCT is specifically suitable for supporting supply-chain-oriented barriers and tracking used materials and products (UMP) through their life cycles for CE adoption. The underlying principle of BCT is a decentralized peer-to-peer system that serves as an intermediary like a bank or government agency. The five disruptive elements of BCT [21] are (1) providing end-to-end visibility of transactions (transparency), (2) providing records that cannot be altered or deleted (immutability), (3) achieving a high degree of security through cryptographic techniques that hinder hacking attempts (security), (4) validating transactions through a consensus among network participants (consensus), and (5) automating business logic via smart contracts. From the perspective of a CE transition, BCT appears to be a technology that can facilitate the management of elaborate communication systems within supply chain management [20,22]. In the building industry, which is characterized by a disintegrated supply chain and low productivity [23], BCT may provide opportunities to enhance efficiency and transparency, with a view to preserving the value of resources over their lifecycles. The primary application of BCT in the context of a CE transition is facilitating the creation of UMP passports to provide transparency and dependable data flow across the entire supply chain network [24].

The successful implementation of a CE transition requires an accurate inventory and documentation of UMP, including product descriptions and their rankings based on their overall properties. BIM is a powerful tool for the documentation and management of information regarding UMP in the building industry. To facilitate documentation and improve the overview of inventories, a digital system based on BCT that can easily be followed up on and that can form the basis for upcoming building projects could be implemented.

The ranking and selection of the most sustainable UMP is necessary to accomplish a CE transition. Solutions based on the multi-criteria decision-making (MCDM) approach are required to provide a realistic insight into the ranking and selection of UMP while considering diverse functional and sustainability requirements, each with associated criteria. The MCDM approach has been employed to solve complex problems by analyzing multiple criteria simultaneously based on both quantitative and qualitative information. In addition, the MCDM approach enables the consideration of the preferences of different stakeholders involved in the decision-making process.

There is a lack of thorough investigation on the potential integration of BCT, and MCDM approaches built on their synergy, capable of enabling broader implementation of a CE in the building industry. The aim of this study is to create a theoretical framework of a digital platform ecosystem for implementing dynamic CE within the building industry through integration of blockchain technology and multi-criteria decision-making approach built upon their synergy.

The structure of this manuscript is as follows: A description of the materials and methods employed is provided in Section 2. The Section 3 provides the theoretical context for CE transition and adoption barriers in the building industry, as well as with respect to BCT, and an MCDM approach for a CE. Our proposed framework is presented in Section 3. Section 4 discusses theoretical contributions, constraints, potential areas for improvement, and prospects for future research. Finally, our conclusions are presented in Section 5.

2. Materials and Methods

An overview of the research methodology, involving a theoretical and practical-level approach, is presented in Figure 1.

2.1. Theoretical Background

2.1.1. CE Transition in the Building Industry

The concept of a CE has become more popular in recent years, but it has not been widely adopted in the building industry despite the industry’s level of waste production and unsustainable use of resources [6,25]. Multiple definitions of CE exist in the literature. Some view it as a remedy for the issues of a linear economy, while others perceive it as being capable of mitigating the negative impacts of linear models via promoting sustainable consumption and cleaner production. CE is considered a strategy for modifying current resource production and consumption methods to enhance efficiency and meet societal needs, ultimately fostering a sustainable environment. However, there are challenges in understanding and implementing CE practices in various industries, including building design, and comprehensive adoption and evaluation of CE in specific projects remain limited. Integrated conceptual models are designed to facilitate CE adoption in the building sector. Bilal et al. [26] perceive CE as a solution to the problems of a linear economy. Ellen MacArthur [27] defines a CE as a system that prevents the negative impacts of a linear economy through the treatment, reuse, and recycling of waste materials, thereby promoting sustainable consumption and cleaner production. Bressanelli et al. [28] believe that CE is a strategy that modifies the current methods of resource production and consumption to improve efficiency and meet people’s needs, ultimately achieving a sustainable environment. Benachio and Tavares [29] found that there is insufficient understanding of the standard practices for CE within the building industry. According to Antwi-Afari et al. [30], circular product design and end-of-life considerations have not been thoroughly examined in previous research. Certain crucial aspects, like circular product design and end-of-life considerations (encompassing quality, economics, and modular integrated construction), have received limited attention in existing studies. Furthermore, a practical CE approach that can effectively merge a comprehensive performance assessment tool with a circular business model for the construction sector is still lacking. To address these gaps in circularity, a research framework comprising eight distinct research themes has been devised [30]. These themes encompass circular design, manufacturing and supply, strategies for CE implementation, end-of-life considerations, CE outcomes and consequences, information exchange, construction processes, and waste management strategies. Hossain et al. [31] argue that the comprehensive adoption and evaluation of specific building projects within a CE context are still limited. Osobajo et al. [32] suggest that while studies have examined resource use within a CE, there is a lack of information regarding building design. Lóopez Ruiz et al. [33] developed an integrated conceptual model for the adoption of CE in the building industry.

The ability to improve circularity in the building industry relies on the capacity to capture built-environment- or building-related knowledge, and the way to gain this ability is by perceiving and aligning digital data-driven concepts throughout the building life cycle. Mêda et al. [34] developed the “Digital data-driven concept” (D3c) to organize, store, and track data, paving the path for a more efficient digital transformation that influences matters related to the circular built environment. The D3c concept involves structuring, storing, and tracking data, facilitating a streamlined digital transformation that impacts circular construction practices [34]. A sustainable and circular economy should incorporate data as a core driver [35,36,37]. When viewed from a data-centric perspective, the relationship between Digital Twin Construction, Digital Data Templates, and Digital Building Logbooks becomes evident, with a substantial number of structured data and information exchange between them. D3c serves as a foundational element for integration, while the incremental maturity levels of Digital Twin Construction serve as a framework for increasing understanding among stakeholders and enhancing projects’ digital capabilities. This data-driven approach ultimately leads to the full implementation of digital twins [34].

Cetin et al. [6] introduced the Circular Digital Built environment framework that was developed based on life cycle stages in buildings and the four core CE principles of regenerating, narrowing, slowing, and closing resource loops. This framework identifies and outlines ten key digital technologies that play a pivotal role in promoting a CE within the built environment. These tools include additive/robotic manufacturing, artificial intelligence, big data analytics, blockchain technology, building information modeling, digital platforms, digital twins, geographical information systems, material passports, and the internet of things. This framework provides a strong starting point for novel research endeavors that combine circular economy principles, digital technology, and the built environment. Moreover, it serves as a source of inspiration for practitioners seeking to drive sustainable innovation in this sector [6].

The Center for Circular Building (CCBuild) is an excellent example of a project that has successfully adopted the CE concept in the building industry in Sweden. CCBuild is an arena where industry players meet and collaborate on re-use and circular material flows during construction, demolition, and circular building management. It is intended to be the industry’s common arena that supports increased circular construction. The arena offers networks, knowledge, and digital services that strengthen the market for circular products and services in the construction and real estate sectors. The work on CCBuild was initiated in 2015 under the leadership of IVL Swedish Environmental Research Institute. In spring 2017, the development of CCBuild continued with the recycling of building materials on an industrial scale. From spring 2019 to spring 2021, the research project “Återbruk Väst” was conducted in collaboration with several partners. More players are welcome to collaborate with CCBuild as associated partners.

Digital technologies play a crucial role in driving the digital transformation of various industries, and they are also seen as essential in the transition to a CE [6,38]. Setaki et al. [39] conducted an analysis of disruptive digital technologies, including BIM, BCT, robotics, AI, additive manufacturing, 3D printing, drones, and digital reality, with the aim of understanding their contributions to a circular building industry. Their research delved into how these disruptive technologies impact the CE throughout the phases of design and engineering, construction, and demolition. In the case of BIM, its advantages in the building industry and from a CE standpoint encompass improved construction process efficiency, optimized design with a focus on material and waste management, and support for innovative CE concepts. As for BCT, its benefits in the building sector and in the context of CE include enhanced functionality, efficiency, and visibility, along with decentralized tracking of information such as material and waste flows.

2.1.2. CE Adoption Barriers in the Building Industry

The necessity of implementing a CE is rooted in the various risks and ambiguities that the worldwide economy faces. The motivation behind this is the pressing requirement to encourage innovation and establish fresh avenues for generating value. Circular economy provides a resilient method with the ability to fulfill these requirements. Within CE, enterprises and their supply chains must shift away from the conventional linear pattern of manufacturing and usage. Instead, they should focus on establishing zero-waste value chains that extend the lifespan of products. This process involves returning materials and products to a system when they are no longer in use, thereby” closing the loop” and reducing or ideally eliminating waste. Essentially, CE fundamentally transforms the way we produce and consume, creating an enhanced ecosystem through waste elimination [40].

Despite the promising advantages of a CE, its practical implementation has been slow, and numerous barriers impede its fruition [41,42,43,44]. Some authors have categorized these barriers into ecological, economic, social, governmental, technological, organizational, and market levels [41,42,44,45,46]. Transparency, traceability, collaboration, coopetition, and insufficient confidence in suppliers and strained relationships at various points in the supply chain stand out as significant obstacles to the adoption of CE practices, all of which have connections to supply chain issues. Additional supply-chain-related barriers include carbon footprints, technology, product recovery, and the flow of returned goods. There is a lack of proper tools with which to reliably calculate carbon footprints [40,47]. Joensuu et al. [48] proposed a method for achieving a fair equilibrium in incentives for both the initial production and the subsequent utilization of building components, without excessively favoring the advantages of reusing them over low-carbon construction technologies. The incorporation of a carbon budget determined through a life-cycle approach will be mandated in building regulations across various nations, necessitating the utmost consistency in the method employed [48]. There exist technological challenges in separating materials, and there is inadequate technology with which to monitor products throughout their entire lifespans. Blockchain has the potential to tackle these issues by offering enhanced transparency in supply chain tracing, facilitating better collaboration and coordination within supply chain networks, establishing greater trust in supply chain ecosystems and strengthening their overall resilience [40]. Blockchain is particularly well suited to overcoming obstacles related to CE adoption within supply chains [40]. This innovative technology can enable supply chains to create innovative CE-driven business models by tracking products and their component materials throughout their entire lifecycles, enhancing the transparency and unchangeability of information and promoting innovation. Blockchain can primarily tackle these challenges via offering greater transparency in managing supply chain traceability, enhancing collaboration and coordination within supply chain ecosystems, fostering increased trust in these ecosystems, and ultimately elevating quality of life through enhanced sustainability practices [49]. Certain barriers, including the expenses related to CE investments and material costs, also affect supply chains. Moreover, challenges stemming from consumer preferences and uncertain demand for recycled materials and products can be viewed as supply chain concerns. In general, these barriers underscore the importance of supply chains in the context of CE. Failing to overcome these barriers linked to supply chains will considerably impede the widespread acceptance of CE practices.

2.1.3. BCT for CE Transition

BCT holds significant promise in addressing sustainability concerns within supply chains, particularly in terms of trust, traceability, and transparency. BCT can play a pivotal role in establishing supply chains with robust traceability and transparency attributes, often leveraging advanced technologies like Radio Frequency Identification (RFID) and Global Positioning Systems (GPSs). This can help manage environmental, financial, and social sustainability challenges [50]. Upadhyay et al. [51] evaluated BCT’s role in the CE, highlighting its potential to enhance performance and communication by fostering trust and transparency among suppliers. Shojaei et al. [20] developed a blockchain-based solution for tracking building components and proactive planning. Wang et al. [19] presented an innovative information management framework for precast supply chains based on blockchain technology, enhancing the traceability of prefabricated components in building supply chains. Elghaish et al. [52] proposed a solution that supports upstream CE design by facilitating collaboration among designers and asset owners in a blockchain network. Leising et al. [53] developed a framework to explore innovative supply chain collaboration approaches that can facilitate the transition toward a circular building sector.

The building industry faces a lack of workable methods capable of facilitating the shift towards circularity, specifically when it comes to combining BIM and BCT. There is a lack of comprehensive solutions that encompass all elements of circularity, involving network structure, business procedures, and products. Furthermore, numerous studies have suggested a shift towards deconstruction using BIM techniques to avoid traditional demolition [54,55,56]. Akinade and Oyedele [57] embraced a circular supply chain approach in conjunction with BIM [58] to create a tool for analyzing building waste patterns and categorizing items using BIM’s computational capabilities. Li and Kassem [59] explored the integration of BCT, BIM, and the Internet of Things (IoT) to enable bidirectional communication between built assets and BIM models. Shojaei et al. [20] investigated the benefits of BCT in the context of the construction industry with a CE focus. Their findings highlight BCT’s capacity to track building materials and products throughout their lifecycles, improving early planning and reuse opportunities. Elghaish et al. [52] put forward a blockchain-based supply chain solution to address the fragmented adoption of blockchain technology in the construction sector and tackle key barriers and challenges in embracing a circular building supply chain.

A summary of the literature involving functions of BIM-based BCT associated with CE is presented in

Table 1. Summary of literature involving BIM, BCT, and MCDM associated with CE.

No	Description	References
	Building Information Management
1	A systematic review of the literature in the area of digital twin and its benefits and proposal of a conceptual framework of Digital twin-Reinforced machine learning to improve production logistics and the supply chain.	[60]
2	Development of a disassembly and deconstruction analytics system to provide buildings’ end-of-life performance assessment from the design stage.	[61]
3	Development of a BIM-based computational tool for building waste analytics and reporting in the construction supply chains using Adaptive Neuro-Fuzzy Inference System (ANFIS)	[57]
4	Identification of existing BIM uses in the construction industry, discussion of their potential to support the implementation of a CE approach, identification and discussion of new BIM uses having the potential to implement CE in the asset lifecycle based on the results of the interviews.	[62]
5	Reviewing the current research on construction waste remanufacturing and the application of Digital Twin in construction and remanufacturing and proposing a concept of potential solutions for the current challenges of construction waste in circular economy.	[63]
6	Formulating a concise, free-to-use Circular Construction Evaluation Framework (CCEF) based upon international design code guidelines to assess and quantify the circularity	[64]
7	Demonstrating the Material Passport (MP) method, which evaluates the recycling potential and environmental impact of materials embedded in buildings on a use case—a demolition object, in order to test its applicability at the end-of-life stage as well as to assess the recycling potential of the existing building.	[65]
8	Proposing a framework for a Digital Platform for Circular Economy (DEEP), integrating various stakeholders and data repositories on the external (inter)- firm and internal (intra)- firm level, using open interfaces.	[66]
9	Proposing a methodology for generating environmental benchmarks for building typologies through a combination of BIM-based LCA tools and machine learning techniques	[67]
10	Adopting an activity-theoretical perspective to explore BIM uses for deconstruction, and involvement in an open-ended and expansive process of implementing BIM in a unique, real-world deconstruction project.	[68]
11	Describing and validating a semi-automated selective deconstruction programming approach for adaptive reuse that can support quantitative analysis, and multiple-target selective disassembly sequence planning, using a rule-based recursive approach for obtaining near-optimal heuristic solutions.	[69]
	Blockchain
12	Presenting a blockchain model and testing through a synthetic case study to provide a proof of concept as to the feasibility of blockchain as an enabler of a CE in the built environment.	[21]
13	Introducing a blockchain technology performance measures in corporating various sustainable supply chain transparency and technical attributes and a new hybrid group decision method, integrated hesitant fuzzy set and regret theory, for blockchain technology evaluation and selection.	[70]
14	Addressing the nascent research field of blockchain for a circular economy and examining current developments by developing and conducting a research-practice gap analysis using a systematic literature review	[22]
15	Providing an overview of Blockchain technology and Industry 4.0 for advancing supply chains towards sustainability evaluate the capabilities of Industry 4.0 for sustainability under three main topics of Internet of things (IoT)-enabled energy management in smart factories, smart logistics and transportation and smart business models	[71]
16	Providing a comprehensive overview of barriers for adopting blockchain technology to manage sustainable supply chains using technology, organizational, and environmental–supply chain and external framework and using the Decision-Making Trial and Evaluation Laboratory (DEMATEL) tool.	[49]
17	New opportunities for implementing I4.0 technologies like Blockchain, AI, Big Data, and IoT for Facilitated Project Management and adopting a circular supply chain for building design and construction	[72]
18	Presenting a systematic and comprehensive overview of blockchain-enabled smart contracts, regarding the operating mechanism and mainstream platforms of blockchain-enabled smart contracts, and proposing research framework for smart contracts based on a novel six-layer architecture	[73]
	MCDM for CE
19	Proposing a new structure for better implementation of CE in constructions and a way to better evaluate this implementation for wooden construction by the means of MCDM methods.	[74]
20	Developing a Circular Economy Composite indicator to benchmark EU countries performance by using a multi-criteria approach to construct a circular economy composite index based on TOPSIS methodology.	[75]
21	Presenting a model using the Analytic Hierarchy Process (AHP) for circular proposal selection in building projects based on a validated conceptual framework	[76]
22	Poposing an integrated decision framework involving Multi-Criteria Decision-Making (MCDM)-based Quality Function Deployment (QFD) method with Hesitant Fuzzy Linguistic Term Sets (HFLTS) to investigate the true potential of blockchain to address the CE adoption barriers.	[40]
23	Applying the LCA consequential methodology to evaluate different methods of constructing residential double-story buildings using the ReCiPe methodology for life cycle inventory considering three different forms of mass timber construction including cross-laminated timber (CLT), nail-laminated timber (NLT), and dowel-laminated timber (DLT).	[77]
24	Combining Sustainability and Circular Economy as two critical performance criteria in the context of building industry projects in order to move toward the integrated assessment model utilizing the Prospective Multiple Attribute Decision Making (PMADM) utilities.	[78]
25	Proposing an integrated framework for the sustainability assessment of Construction and Demolition Waste management based on the integration of existing methods: bottom-up materials stock approximation; cost–benefit analysis for criteria calculation; and scenario and multi-criteria decision-making analysis for sustainability.	[79]
26	Proposing a topological interlocking system for designing reusable modular components that maximize sustainability. using a two-stage evaluation method (AHP-TOPSIS) to construct an evaluation index based on the design and material of a building component.	[80]
27	Developing a decision support system (DSS) to select the most appropriate concrete waste management method using Delphi technique and the fuzzy analytic hierarchy process (FAHP) to analyze the decision-making structure and consider factors related to the waste management methods.	[81]
28	Examining the factors that obstruct the incorporation of CE in the built environment or the construction sector in India identifying a total of sixteen barriers hampering the adoption of CE in built environment and categorized under six categories of economic, environmental, technical, societal, governmental, and behavioral barriers by using DEMATEL method to analyze the barriers and develop a cause-effect relationship among them.	[14]

.

2.1.4. MCDM Based Approach for CE Transition

There are several methods based on the MCDM approach, such as Simple Additive Weighting (SAW), the Analytic Hierarchy Process (AHP), the Analytic Network Process (ANPs), TOPSIS, PROMETHEE, DEMATEL, COPRAS, and VIKOR, that are commonly used to support the selection of optimal alternatives in engineering projects [82]. Recent studies have shown the feasibility of using the MCDM approach to measure all aspects pertaining to sustainability, such as the impacts of plastic waste management in Norway, assessing environmental impacts in product lifecycles, evaluating the benefits of eco-industrial parks in China, and deciding on suitable waste-to-energy generation technologies to apply in Bangladesh [83,84,85,86,87]. MCDM approach has been applied in various CE contexts, including identifying skills required for project managers, evaluating strategies for transitioning buildings to a CE, and assessing barriers to implementing Industry 4.0 technologies in CE [88,89]. However, there appears to be a gap in the current literature in terms of the MCDM approach specifically promoting circular decision making, rather than just considering sustainability in general, in real-life project situations.

MCDM approach within CE deals with the ranking and selection of UMP, which are subject to several objectives with associated criteria. The prioritization and the utility degree of UMP directly depend on a system of criteria adequately describing the alternatives, values, and weights of the criteria [90].

3. Proposed Framework

In this study, a theoretical framework for a digital platform ecosystem was developed with a focus on a implementing a dynamic CE in the building industry through the integration of BCT and an MCDM approach. The flowchart of the framework is presented in Figure 2. A description of the different topics in the flowchart is presented in the following subsections.

3.1. Existing Building, Demolition, Product Bank, Marketplace, MCDM, and New Building

In the first step, an inventory of UMP in an existing building will be conducted to provide an idea of what can be reused in a new building project when the demolition of an existing building is scheduled. Through inventory, products can be quantified and thus more easily put into context during the design phase of a new building project. The inventory should be conducted during the preliminary study phase to provide a basis for reuse in the design phase. Planning regarding reuse is facilitated via clearly set goals regarding reuse in the project as well as clear guidelines on what is to be reused and to what extent. Inventory is important for both future recycling work in the project and for creating clear boundaries and goals in new building projects. Furthermore, inventory must focus on the reuse potential based on the functional and esthetical conditions of the UMP. Thus, careful demolition is required to preserve UMP by sorting the demolition waste according to given categories. Unlike conventional demolition, consideration and caution are required during disassembly to avoid damaging building materials and products and the eventual need for upcycling. Upcycling means that recycled materials and products undergo a refining process to grant them greater use value and allow them to be able to meet the requested requirements. After upcycling has taken place, intermediate storage of the materials and products is often needed in the reuse process before this process can be implemented again. Product descriptions and documentation are often missing for UMP, making it difficult to ensure that the UMP meet the requested requirements. The digital interface of a product bank functions as a web-based database for UMP and must be synced with a product marketplace, which can be either web-based or a mobile-based app. A web-based product marketplace is for either finding and claiming reusable UMP or finding actors who offer circular services.

3.2. Life Cycle Information Exchange, BCT, Smart Contract, and Digital Interfaces

Lifecycle information exchange in a building involves the process of sharing and transferring comprehensive data, documentation, and knowledge throughout the entire lifespan of a building, that is, from its inception to its eventual decommissioning or repurposing. It involves the seamless flow of information among various stakeholders involved in the different stages of a building’s lifecycle, including designers, contractors, facility managers, building owners, and occupants. Life cycle information exchange plays a crucial role in optimizing building performance, reducing operational costs, enhancing occupant comfort and safety, and promoting sustainable building practices. By facilitating effective communication and collaboration among stakeholders, it enables a more holistic approach to building management and maintenance, leading to improved efficiency and better outcomes throughout a building’s lifespan.

BCT offers a decentralized and transparent platform for securely exchanging and storing this information. By utilizing BCT, stakeholders can contribute and access relevant data, such as those regarding environmental performance, material composition, and maintenance history, fostering a collaborative approach to sustainability. BCT-based marketplaces provide a digital platform for sharing and trading building materials and components, enabling the establishment of a product bank. The idea behind such marketplaces is that the industry players, as buyers and sellers, can meet and collaborate on matters regarding used materials and products during construction and demolition projects. The bank serves as a repository of reusable and salvaged items from existing buildings, supporting a CE by facilitating these items’ integration into new building projects. Through blockchain’s immutable and transparent nature, the origins and characteristics of these components can be verified, instilling trust among stakeholders and encouraging these components’ reuse.

The definition of a smart contract pertains to a digital protocol responsible for carrying out predefined commitments or conditions agreed upon by the involved parties [91]. Smart contracts are automated, self-sufficient procedures deployed over blockchain to enforce agreements between buyers and sellers, undergoing automatic verification and execution through a computer network [92]. Ethereum provides a programming language known as Solidity for the implementation of smart contracts [93]. Smart contracts, powered by blockchain, automate and enforce agreements between parties involved in the building process. These self-executing contracts ensure compliance with predefined sustainability criteria and facilitate seamless transactions within the marketplace. For instance, when a building project requires specific materials, smart contracts can automatically search the product bank and complete a purchase based on predefined criteria, such as environmental impact or cost-effectiveness.

Digital interfaces play a leading role in facilitating the exchange of information and decision-making processes. Through user-friendly interfaces, stakeholders can access and contribute to shared data, enabling seamless collaboration and decision making. These interfaces should be designed with the principles of user experience and accessibility in mind, ensuring that all stakeholders can actively participate in the exchange of life cycle information.

3.3. MCDM Approach and Selection of Most Functional and Sustainable Materials and Products

The MCDM approach is invaluable in evaluating the functionality and sustainability performance of available UMP. By considering multiple criteria, such as functional and esthetical conditions, environmental impact, economic viability, and social considerations, MCDM enables informed decision making that aligns with circular principles. Integrating MCDM into blockchain-based marketplaces allows potential buyers to select sustainable alternatives based on their comprehensive and objective evaluations.

To provide an example of the application of an MCDM approach, a case study has been performed. The scenario in the case study is as follows: A project leader for a construction project is looking for used freezers at the digital market; he/she serves as a hypothetical buyer. He/she enters the digital market and finds two different interesting alternatives. The digital market offers an MCDM approach to ease the ranking and selection of alternatives based on the judgement of the project leader. This case study deals with the ranking of two used freezer alternatives produced by two brands available in the marketplace. The considered criteria are functionality, product information data, and cost. The criteria, metrics, and units of measurement are presented in

Table 2. Selected criteria, corresponding metrics, and units of measurement.

Criteria	Metrics	Units of Measurement
Functionality	Functional condition	Five-star rating scale
Product information data	Product information	Five-star rating scale
Cost	Expenses	SEK, SEK/m, SEK/m2 or SEK/m3

.

To set the criteria weights, three questions concerning the pairwise comparison of the criteria by the hypothetical buyer must be answered:

➢

Functionality against product information data;

➢

Functionality against cost;

➢

Product information data against cost.

The hypothetical buyer is supposed to compare the criteria based on his/her experience/views using a nine-degree weighting scale (the details of which are presented in

Table 3. Fundamental weighting scale in pairwise comparisons.

Extremely less important	1/9
Very strongly less important	1/7
Strongly less important	1/5
Moderately less important	1/3
Equal importance	1
Moderately more important	3
Strongly more important	5
Very strongly more important	7
Extremely more important Immediate values between above Scale values	9 2, 4, 6, 8

).

Summarized results from the pairwise comparisons made by the hypothetical buyer are shown in

Table 4. Summarized hypothetical results from the pairwise comparisons made by the hypothetical buyer.

Criteria	Functionality	Product Information Data	Cost
Functionality	1.0000	5.0000	3.0000
Product information data	0.2000	1.0000	0.3333
Cost	0.3333	3.0000	1.0000

.

Inconsistency in the decision matrix can occur if the judgements for the pairwise questions are directed to several hypothetical buyers with different types or levels of experience or different views. To ensure the consistency of the subjective judgements of the hypothetical buyer in his/her judgement for the pairwise comparisons in Table 4, the consistency ratio (CR) was evaluated using the eigenvalue problem [94]. The eigenvalue problem was solved, and the eigenvalues (λ) were calculated as the entries in the main diagonal, with λ_max equal to 3.0385 serving as the highest positive eigenvalue. The value of CR was determined to be 0.0331, which satisfies the condition of CR < 0.1 according to [95]. The weightings of the criteria are summarized in

Table 5. Weightings of the criteria.

Criteria	Weightings
Functional condition	0.6333
Product data	0.1062
Cost	0.2605

.

The summarized outcomes for the assessment of freezer alternatives are presented in

Table 6. Summarized outcomes for the evaluation of freezer alternatives by the hypothetical buyer.

Alternative	Maximizing Functionality	Maximizing Product Information Data	Minimizing Cost
Freezer, brand A	5	2	1/1500
Freezer, brand B	4	2	1/1400

.

Consequently, the priority order of the two compared alternative freezers based on the AHP method could be calculated by multiplying the column-normalized matrix in Table 6 by the weightings column vector in Table 5 in order to attain the scores column vector. Thus, the freezer from brand A with the higher score, 0.553, was chosen as the optimal alternative. Brand B had a score of 0.447. It is very important to apply sensitivity analysis by revising the weightings of the criteria in order to ensure the reliability of the final decision.

3.4. Smart Contract

A smart contract was developed using the Remix Ethereum platform and the Solidity programming language, as shown in Figure 3. The result of the evaluation of design alternatives determined using the MCDM approach (shown in Section 3.3) was reported and processed in the developed smart contract. The smart contract encompasses various functions, such as “Add functional condition”, “Add product information”, and “Add expenses”, which allow users to input data into the smart contract, and the “Report the most optimal alternative” function checks the evaluation of the alternatives by using programmed thresholds. The metrics’ functional condition, product information, and expenses for the two alternative freezer brands were evaluated. The information regarding the selection of the brand A freezer as the most optimal alternative was reported. This check was conducted when a specific evaluation of the alternatives was provided.

Depending on the degree of abstraction employed for modeling and analysis, the formalization methods for smart contracts can be categorized into two primary groups: program level and contract level [92]. Remix is a tool used at the program level for developing and interacting with Ethereum smart contracts, while formal methods can be applied at the contract level to formally specify and verify the properties of the contract.

3.5. Benefits of the Proposed Framework

The proposed framework provides a solution by allowing owners/authorities to share scanned BIM products and components for reusable items in new designs. It also enables designers (architects/engineers) to create and share BIM products and components when owners lack BIM objects for reusable items. Furthermore, it supports collaboration between owners, asset operators, designers, and contractors in a blockchain network, facilitating the integration of CE principles. This integrated approach, which links BIM, BCT, smart contracts, and the MCDM approach, sets this framework apart from others in the field and supports the transition to a dynamic CE.

One key aspect of this framework is the promotion of building component reuse to reduce waste generation during refurbishment and demolition. Designers (architects/engineers) can use this framework to check the availability and assess the usability of building components for new projects. Additionally, this framework provides a secure environment for asset owners to share building components, including details such as types, quantities, prices, and real images. Access to this information is limited to authorized parties via a designated application programming interface (API).

The proposed framework encourages decentralized interaction among practitioners and incentivizes designers to share BIM products and components based on existing elements. By doing so, more designers (architects/engineers) can recycle these BIM resources in new projects, making component reuse a mainstream practice in building.

Furthermore, the framework allows property owners to assess the worth of items they can reuse and salvage. This supports informed decision making regarding deconstruction at an early stage of a project. During the pre-demolition phase, owners and designers (architects/engineers) can collaborate to identify purchasable items and determine deconstruction outcomes based on data-driven decisions.

After the primary operator sets up the blockchain network and smart contract features, asset operators can enroll their assets and initiate the process of sending and receiving functions. The key goal of a circular supply chain is to optimize the value of resources and promote reuse. Designers (architects/engineers) acquire entry to the blockchain network to exchange information about new design products and components as well as to create BIM elements for current elements.

Efficient operation of the blockchain network relies on essential transactions. These include the BIM model’s “Update” function, which tracks the progress of new BIM product and components throughout the design process. Another transaction updates the Asset Information Model (AIM) when an existing building incorporates BIM. These transactions enhance collaboration between asset operators and designers (architects/engineers). Additionally, the framework facilitates purchasing and selling processes through various transactions such as requests, purchase, and delivery. The network is designed to be accessible, allowing new asset operators to register their assets and features at any time using the new assets operator transaction.

The proposed framework suggests that a municipality serves as the main authority, responsible for developing and managing the permissioned blockchain network. The municipality enables all smart contract functions and ensures that authorized parties can invoke transactions. To accommodate asset operators with varying levels of IT proficiency, the framework includes the development of a user-friendly API. This API allows authorized but unregistered parties to invoke transactions, while a private API restricts the recording of new blocks to registered blockchain parties (i.e., asset operators and designers). To ensure compatibility with BIM, this framework supports the recording of various information formats, including PDF, JPG, and DWG files.

By facilitating the development of BIM products and components like existing building elements, the proposed framework promotes reuse. These products and components are exported as IFC files, enabling asset operators to utilize them with any BIM platform. Designers can record BIM products and components in the blockchain network, reducing the need to start new projects from scratch. This framework applies to building maintenance and demolition preparations, allowing operators to classify elements into reusable items, salvaged items, and unsalvageable items/materials. The smart contract is then utilized to manage requests from designers and record new items with specifications and real images. This framework also accounts for the option of selecting Scan-to-BIM products and components, thereby saving resources by utilizing existing BIM resources for reusable building items or facilities.

To conform with the ISO 19650 [96] series, a widely accepted set of standards regulating BIM project implementation, the proposed framework can be seamlessly incorporated into the ISO 19650 design phases. Owners can clearly express the requirement for a BIM UMP within their employer information requirements during the assessment and planning phase. When awarding contracts, the lead appointed party can take this stipulation into account when allocating resources in response to tenders. The common data environment functions as a repository for information containers from the blockchain network during the design phase. This enables the appointing party and lead appointed party to evaluate the performance of items or facilities during operation and use these data in future projects to facilitate the shift towards a CE. Furthermore, this framework can serve as a secure common data environment with expanded smart contract capabilities, including the addition and retrieval of areas within the common data environment along with an endorsement policy to govern information access by various stakeholders.

The sustainability of information is crucial for the functionality of the proposed framework. Authorized and registered designers (architects/engineers) can access recorded UMP, promoting their reuse in new projects. The blockchain network, managed by the municipality, allows for global data sharing, including international item delivery if it is economically viable. As business requirements evolve, new smart contract functions can be added to the existing blockchain network. For instance, a sub-category like “reusable items from historical buildings” can be introduced. Material suppliers can take part in the network, purchasing materials from and selling them to designers. This comprehensive approach maximizes the value of various materials while minimizing environmental impacts.

To facilitate block recording (information) by all parties, a private API can be developed, offering a user-friendly interface. This interface allows authorized parties, regardless of their IT skills, to interact with the blockchain network, upload documents (e.g., IFC files, real images, and specifications), and reuse UMP in new projects. This fosters the adoption of a building circular supply chain and encourages designers to develop an extensive library of BIM objects for existing building items over time.

4. Discussion

The transition to a CE in the building industry requires a comprehensive understanding of the life cycle stages in the built environment. Circular building strategies are designed to optimize resource efficiency, minimize waste generation, and extend the lifespan of buildings. This involves adopting sustainable practices from the design phase to demolition and recycling. The development of circular business models plays a crucial role in driving this transition by promoting collaboration, resource sharing, and the reuse of materials. Enabling digital technologies further enhance the circularity of the built environment by facilitating the tracking and monitoring of material flows, facilitating efficient resource management and promoting transparency. By establishing a well-defined building material flow system, the building industry can achieve significant reductions in waste generation and environmental impacts while also fostering innovation and sustainable growth.

Challenges related to existing regulations and guidelines in the construction industry hinder the adoption of CE principles [97,98,99]. These regulations were typically designed without considering a CE’s resource efficiency and waste reduction goals. Permit and zoning constraints, waste management regulations, and health and safety requirements may not align with CE practices, adding to complexity and cost. Additionally, taxation structures and procurement policies that prioritize cost-effectiveness can deter CE investments. To address these challenges, stakeholders can advocate for CE-friendly regulatory changes, promote education and training, and encourage collaboration among industry, government, and organizations to develop policies that incentivize sustainable and circular practices.

BIM-enabled demolition waste management is revolutionizing the building industry by integrating BIM technology into the process. BIM-based deconstructability assessment allows for the efficient planning and execution of demolition activities, optimizing the recovery and recycling of materials. To enhance the traceability and transparency of material flows, a blockchain platform can be employed. This platform provides a comprehensive and reliable system for tracking information and material traceability, ensuring transparency throughout the entire supply chain. Blockchains have also emerged as enablers for assessing cooperative CE networks, promoting collaboration and resource sharing among stakeholders. Furthermore, the combination of BCT with smart contracts offers an attractive and efficient alternative to centralized asset-monitoring systems for environmental regulators. By leveraging BCT, sharing reusable items as BIM families becomes more feasible, fostering a culture of resource reuse and reducing waste generation in the building industry. For the verification of smart contracts using formal methods, lowering the cost and execution time of formal approaches in various verification phases and simplifying and increasing the accessibility of formal methods for software developers and testers are recommended [92].

The implementation of decision support systems is crucial for minimizing waste in the building industry. These systems provide valuable guidance and analysis for various stages of waste management. Decision support tools aid in the on-site sorting, reuse, and recycling of wasted materials, enabling building companies to make informed decisions on how to best manage and divert waste from a landfill. Additionally, decision support systems assist in selecting the most suitable demolition techniques, considering factors such as environmental impact, cost-effectiveness, and safety. They also facilitate demolition assessments, helping to evaluate the feasibility and potential outcomes of demolition projects. Waste sorting and measurement are further supported by decision tools, providing guidance on efficient waste-sorting practices and accurate measurement techniques. By leveraging these decision support systems, building companies can optimize their waste management strategies, reduce environmental impacts, and contribute to a more sustainable built environment.

5. Conclusions

This study reviewed the dynamic circularity within the building industry through the integration of BCT and the MCDM approach. It introduced the CE transition in the building industry, the need for an integrated BCT and BIM environment for the CE transition, the CE adoption barriers, and an MCDM-based approach for CE transition. We developed a theoretical framework for a digital platform ecosystem with a focus on CE within the building industry through the integration of BCT and the MCDM approach.

This study highlights the key aspects of transitioning to a dynamic CE in the building industry. It emphasizes the importance of understanding life cycle stages, adopting circular building strategies, and developing circular business models to optimize resource efficiency and minimize waste generation. This study also underscores the role of digital technologies, such as BIM-enabled demolition waste management systems and blockchain platforms, in enhancing transparency, traceability, and collaboration within the industry. Moreover, the study focuses on the barriers regarding the adoption of CE and underlines the absence of regulatory standards, government support, and CE knowledge among decision makers; the inadequate tools available for calculating carbon footprints; technological challenges in material separation; and the lack of monitoring, transparency, and trust in supply chains. Additionally, this study emphasizes the significance of decision support systems in waste management, including with respect to on-site sorting, selecting demolition techniques, demolition assessment, and waste sorting and measurement. Implementing these systems can lead to reduced waste and environmental impacts and promote sustainability in the building sector.