3.2. Content Analysis
Research topics
As awareness around sustainability increases and concerns regarding the economic, social, and environmental consequences of CDW generation intensify, attention is shifting towards repurposing waste into valuable resources. To achieve this, the primary aim is to embed circular strategies within CDW management practices, necessitating a multi-faceted and interdisciplinary approach that bolsters the decision-making process [
23,
24]. Research directions are diverse and include a range of assessment methodologies, subjects, geographical regions, and management levels, examined either broadly or in specific combinations. The primary themes identified from the reviewed articles are illustrated in
Table 1.
It is possible to minimize and manage the production of CDW at every stage: pre-construction, construction, building renovation, waste collection and distribution (the end-of-life stage), as well as material recovery and manufacturing, more effectively. Recycling is often the main topic of CDW management, with recovery and reuse gaining momentum as frameworks for the implementation of various recycling and recovery procedures are developed and backed by case studies. Concepts such as design for deconstruction [
2,
37], urban mining [
12,
21,
47], selective demolition [
6,
44], adaptive reuse [
50,
51], reverse logistics [
6,
36,
52], and closed-loop systems are increasingly being explored. Generally, research tends to focus on the analysis of CDW generation, CDW treatment methods, enhancing the technical properties of products with recycled material content, and the human aspect of CDW management.
CDW consists of waste produced throughout all phases of a building’s life cycle, leading to significant environmental consequences. Certain scholars also incorporate waste management from transport infrastructure into their investigations, acknowledging its capacity for utilizing recycled construction materials and its essential function in promoting a more circular method in the industry. As for research that deals with the management of CDW in the built environment from a life cycle viewpoint, full life cycle analyses are frequently employed, as illustrated in
Figure 7.
A large number of academic papers concentrate on the cradle-to-grave strategy for CDW management, investigating every phase of a structure’s lifespan. Adopting this viewpoint can benefit all stakeholders and society at large, as it provides a blueprint for deconstruction or demolition with an extended lifespan for recycled materials in the design phase. It also enables planning for construction and maintenance that minimizes resource consumption, ensuring the preservation of the value and quality of materials during operation.
Most of the research is concentrated on the end-of-life strategy, primarily because most construction components are not designed with deconstruction in mind. In order to prevent the growing accumulation of CDW, it is crucial to discover strategies, technologies, and regulations and gain stakeholder support to manage the reduction, reuse, recovery, and recycling of waste in a sustainable manner.
CDW Management Strategies and Treatment Solutions
The primary objective of CDW management strategies within the Circular Economy (CE) is to divert CDW from landfills, thus preserving the inherent value of materials and products, keeping them within a closed loop, and transforming waste into valuable resources. These strategies are based on the waste hierarchy endorsed by the Waste Framework Directive and follow the 3R, 4R, 6R, or 9R strategies in line with a whole life cycle approach. CE and waste hierarchy advocate for waste management through reimagining, reengineering, and repurposing to amplify resource efficiency and mitigate waste production and its detrimental consequences. The subtle discrepancy is that the waste hierarchy still allows for disposal, while the circular economy model does not [
53]. According to the waste hierarchy, the least preferable method of waste treatment is disposal, commonly through landfilling in the construction and demolition sectors. This is followed by the recovery phase, which manages residues through burning and, occasionally, backfilling. The best CDW management strategy is prevention, followed by waste reduction, reuse, and recycling. An efficient CDW management strategy must prioritize according to the waste hierarchy, the building’s life cycle stage, and available economic, regulatory, technical, and educational tools. The CE framework consists of four key elements: 1. sustainable business model innovation, 2. closed-loop systems, 3. product-service system, and 4. innovative sustainable business models aim to significantly diminish the adverse environmental effects of construction waste. The focus of closed-loop systems is on resource preservation during product design and creation, whereas product-service systems tend towards providing a service rather than products as their primary business strategy [
54].
The waste hierarchy’s five layers merely provide general guidelines for CDW management. Strategy development and policy formulation must consider the specific situation to which they apply, guiding increased circularity in CDW management in the future.
The first strategy to avoid waste generation and preserve natural raw materials is prevention. This strategy primarily refers to the pre-use phase of buildings, i.e., the design, construction, and production stages. From the 9R strategy, it involves refusing, rethinking, and reducing potential waste generation. Minimizing construction waste during the design stage and construction operation could be a more cost-effective approach compared to remedial actions. For the design stage, the main methods and tools developed and analyzed in the sample articles refer to design out waste, design for disassembly or deconstruction, pre-cast construction, and modular construction design. In terms of operations before construction begins, scholars highlight the importance of a site waste management plan. This involves identifying waste streams and establishing tools for monitoring, collection, and the promotion of appropriate waste management practices, complete with quantifiable indicators and objectives. Roughly one-third of waste production at a typical construction site is due to the designers’ failure to incorporate waste prevention methods during the design phase [
55]. Material use reduction is enhanced both by the design of circular buildings and by the site waste management plan, accompanied by efficient construction material procurement.
The emphasis of reuse is on prolonging the life of structures and incorporates the strategies of reusing, repairing, refurbishing, remanufacturing, and repurposing from the 9R methodologies. The best option for CDW management is to reuse the entire building. In many cases, the first end-of-life (EoL) strategy is demolition, as most of the buildings were not designed for disassembly. However, selective building deconstruction or adaptive reuse is an alternative to demolition. Reusing materials encompasses the continual application of materials in similar construction operations or their incorporation as new components in alternative processes. Typical uses for repurposed demolition waste materials include land restoration, road construction, and replacing concrete aggregates [
2,
50,
51,
56].
Recycling is the most studied strategy, and it covers the post-use phase of the building stock, implying the useful application of materials. The objective of recycling is to convert CDW into new products suitable for reuse in the construction industry or other economic sectors. By preventing the wasteful disposal of potentially useful materials that would otherwise be discarded in an environmentally harmful or costly manner, recycling simultaneously reduces the demand for new, unprocessed resources [
28]. Recycling involves the on-site sorting of materials and their reprocessing to convert them into new products. Down-cycling and up-cycling differentiate between recycled materials with lower or higher quality or functionality compared to the original product. The expenses associated with handling and recycling construction and demolition waste (CDW) for the secondary production of value-added items can be substantial, given steps like material screening and reprocessing. This places a significant financial burden on companies specializing in CDW treatment, pressuring them to generate profit [
48]. The most recycled material in the construction and demolition sectors is concrete for concrete recycled aggregates. The revised WFD introduced the end-of-waste (EoW) criteria to promote recycling and transform waste into valuable resources. EoW criteria fix a set of conditions that, when fulfilled, make waste cease to be waste and can be regarded as a freely marketable material. After a recovery process, if waste has a useful purpose and there is demand for it, complies with the specific technical requirements and standards applicable for similar raw materials, and does not impose risks on human health or the environment, it can be considered that it has reached EoW status. The main objectives of the EoW criteria are to remove bureaucratic burdens, encourage recycling, promote the quality of recycled materials, and develop secondary material markets.
CDW management has a complex task for which the mentioned strategies and methods must be applied contextually and in combination to create a circular use of materials and support the goal of sustainability. To achieve this, efforts need to be made to develop the entire value chain: firstly, reusing or recycling resources in such a manner that most of the material value is conserved and recovered at the end of the building’s life; and secondly, designing components and using various construction methods for reuse [
57].
In creating a strategy for efficient waste management in the construction and demolition sectors, other aspects need to be considered, such as transport, regulations, issues about the quality of recycled material, disposal costs, innovative recycling technologies, or economic incentives [
58]. All these aspects need to be created in such a way that they support each other and enhance circularity and sustainability. The key to an effective waste management system is the involvement of stakeholders at all levels and phases of the process of creating a sustainable development strategy. The importance of stakeholder involvement and behavioral patterns to identify suitable solutions for identified barriers in the implementation of circularity principles in CDW management has been analyzed and stated by the authors in the reviewed sample.
Table 2 presents the involvement of stakeholders in research to provide efficient solutions.
Sustainability assessment
In order to meet the goals of the circular economy, the effectiveness of construction and demolition waste (CDW) management strategies must be evaluated. The significance of sustainability in current and future endeavors, guided by principles of design-led circularity—the eradication of waste and pollution, the sustained circulation of products and materials, and the regeneration of natural systems—cannot be overstated. Many studies have explored the impacts of CDW management, often utilizing the life cycle assessment (LCA) methodology, which is established by the ISO 14040 standard.
The LCA approach is designed to assess the economic, social, and environmental impacts of a product, service, or activity. It involves four stages: setting the goal and scope, conducting a life cycle inventory (LCI), executing a life cycle impact assessment (LCIA), and interpreting the results. Underpinning LCA is a cradle-to-grave framework, encompassing the entire lifecycle of a product—from the extraction of raw materials through its production and use to its final disposal at the end of its lifespan. The LCA method provides a valuable resource for gauging the environmental influence of a product, not just during its production phase but throughout its entire life cycle. In the context of CDW management, LCA allows for a comparative evaluation between recycled and virgin materials, thereby substantiating its environmental sustainability.
In the literature review, most LCA studies contrasted the environmental impact of natural aggregates with recycled aggregates. However, some studies also evaluated the effect of waste management strategies in different scenarios. For example, [
14] performed an LCA for three scenarios in Italy’s Campania Region, assessing economic and environmental impacts as well as land use impacts for the landfilling case, the status quo case, and the best-case scenario, where advanced selective demolition and treatment techniques were implemented. The LCA studies with impact categories and the goal and scope definitions are illustrated in
Table 3.
Quantification tools and forecast methods
To assess the efficiency of CDW management, a framework incorporating methods, tools, and instruments is required, which can underscore the progression of efforts. Decision-making about recycling, material reuse, or recovery gets obstructed and can result in errors due to the imprecise quantification of CDW. The unavailability of precise data on building materials and components is a global issue.
The majority of studies use calculation methods like the “waste index” and the material flow analysis (MFA), which are based on data gathered from registries and field research. MFA is a method extensively utilized in CDW management for building stock and flow accounting. This is based on the principle of mass conservation, which asserts that the sum of material inputs always equals the sum of material outputs plus the material stored within a system, defined within a specific spatial and temporal context [
21]. The bottom-up MFA approach uses the material intensity coefficient (MIC) [
67]. The building inventory is segmented into distinct material sections according to their application, and the volume of materials in these sections is determined by multiplying the physical parameters of the specific section size by the material intensity per capita (MIC). However, as MIC data is typically site-specific and not easily accessible, researchers must infer this data from a variety of sources, such as site surveys, architectural data, construction norms, blueprints, cadastral maps, energy requirements, or corporate data. This results in a procedure that is both laborious and time-consuming [
21]. Data availability plays a crucial role in reducing uncertainties and preventing inaccurate stock estimations.
The analysis of building stock and flow delivers critical quantitative information for predicting future CDW generation and modeling estimated stock and flows for scenario-based circular waste management. MFA is an essential model for formulating circular economy strategies and provides an ideal tool for a thorough assessment of material flows and inventories, as well as their potential for recovering value from waste [
33].
Table 4 illustrates the usage of MFA in the reviewed literature.
New assessment models have been developed using MFA and geographic information systems (GIS). The combination of MFA with GIS has evolved into a potent tool for analyzing and interpreting material building stocks and CDW flows to create circular strategies [
33].
The quantification models using GIS are presented in
Table 5.
The creation of a sustainable and circular scenario needs dependable and error-free data, which can be fulfilled through digital models of buildings. Building information modeling (BIM) allows for the creation of a 3D digital model of a structure, encapsulating both geometric and non-geometric properties of all components. BIM facilitates the automatic acquisition of the total volume of materials, their attributes, and the dimensions of the object. BIM is a smart, object-oriented model where any quantitative or qualitative change to an object is reflected throughout the model’s views and sections [
71].
Building information can be efficiently exchanged and conveyed via a unified platform across the lifespan of a project. This makes it well-suited for design synchronization, material quantity evaluation, 4D planning, and cost projection, all of which are crucial for CDW management. Through accurate forecasting of waste output, the order of waste creation, and disposal expenses, BIM can assist in making informed decisions regarding CDW management planning [
2].
The BIM method fosters a collaborative environment in construction by using a digital representation of the building. It amplifies circularity in the CD sector by aiding decision-making in waste reduction and prevention through BIM-based deconstruction frameworks, BIM-assisted waste management, material and component banks, BIM-based LCA, and BIM-based DfD, as well as through visualization and simulation of waste performances and waste management reporting [
54].
Table 6 presents the BIM literature and the development of BIM tools found in the review sample.
Recycled materials
Waste from construction can be sorted either by its source or its characteristics. When sorting by characteristics, researchers have divided waste into physical waste (remaining debris) and non-physical waste (cost and time overruns). As for the source, the waste could be anthropogenic (public construction and maintenance work, building construction, renovation, and demolition) or natural (earthquakes, floods, hurricanes, and tsunamis).
Concerning materials, academic research often focuses on the recycling of concrete and enhancing the mechanical properties of recycled concrete aggregates for use in mixtures of cement, mortar, and recycled concrete. Every component of construction and demolition waste (CDW)—from concrete [
10,
46,
55], bricks [
34,
72], tiles, timber [
73], glass, gypsum, asbestos [
74,
75], plastic, and cardboard [
68]—is the subject of numerous studies. There’s also interest in exploring the potential for recovery and recycling of materials like wood [
76], bricks, and insulation [
44,
77], and the use of mineral waste fractions for water filtration [
78].
Concrete forms the largest fraction of CDW, ranging from 32% to 75% depending on the source [
79]. It constitutes 40 to 80% of total on-site waste. New buildings can generate 18 to 33 kg of waste concrete per m
2 of built area when utilizing concrete structures. Residential building demolition can result in up to 840 kg of waste concrete per square meter demolished. Concrete is widely used globally, making it the most popular building material, excluding excavated materials [
25,
55].
In
The European List of Waste, concrete waste falls under code 17 01 01. As per the waste hierarchy, end-of-life (EoL) concrete treatment levels are ranked [
47]:
Preventing EoL concrete;
Reusing concrete components;
Recycling waste into aggregates for use in concrete production;
Recycling waste into aggregates for road construction or backfilling;
Landfilling.
Despite landfilling being the least preferable waste treatment method, a significant fraction of concrete ends up in landfills. Repurposed concrete aggregates (RCA) are applicable for uses such as filling in road sub-bases, in hydraulically or bitumen-bound formations, rigid pavement construction, and as a component in concrete manufacturing [
25,
55,
80]. The most common recycling process is crushing CDW to create secondary aggregates based on required mechanical properties and strict standards (like EN 12,620 aggregates for concrete or EN 13,242—aggregates for unbound and hydraulically bound materials for civil engineering work and roads).
For inert waste containing concrete, recycling CDW into RCA to produce recycled concrete (RC) is a key strategy for reducing the environmental impact of the construction and demolition sectors. While RCA is of high quality, its cost and purity requirements can limit the feasibility of recycling. RCA, usually derived from pulverized pre-used concrete structures, is required to adhere to particular quality criteria. They should be devoid of impurities such as sulphates (originating from plaster), clays (coming from bricks or tiles), or an overabundance of fine materials [
10,
46].
Portland cement, a principal ingredient in concrete and various cement-based materials, is frequently employed. Nevertheless, its manufacture is both energy-demanding and environmentally detrimental, given the substantial use of natural resources during clinker production and rotary kiln operation, accounting for around 6–7% of total CO2 emissions.
Prior studies [
46,
80,
81] have indicated that compared to natural aggregates (NAs), recycled aggregates (RAs) tend to have increased porosity, decreased density, reduced mechanical strength, and lessened durability owing to the presence of sulphates and chlorides. They also exhibit reduced workability because of their porous nature, contain a higher percentage of fine particles, absorb more water, and possess a greater friability coefficient. Several studies [
46] have discovered that combining recycled aggregates (RAs) with other industrial by-products such as fly ash, coal bottom ash, blast slag, silica fume, plastics, and rubber tires can have advantageous effects in certain situations.
Morón et al. [
81] carried out lab experiments to assess the physical and mechanical characteristics of cement mortars made with recycled concrete aggregate (RCA) and strengthened with aramid fiber. They tested six mixtures, with results indicating that the inclusion of aramid fibers in mortars created with RA increased the flexural strength, albeit not to the level of mortars made with natural aggregate (NA). The experiment also showed a reduction in capillary water absorption, while the aggregate’s density and surface hardness remained the same. The research concluded that adding aramid fibers to RA reduced the adhesion of mortars, increased resistance to freeze–thaw cycles, and lessened shrinkage of mortars prepared from RA with aramid fibers compared to recycled mortars without fibers.
Jesus et al. [
31] evaluated the decrease in cement content in render mortars with RCA and recycled mix aggregate at three different ratios. The findings indicated that mortars with a lower cement ratio and a concurrent incorporation of 20% RCA performed quite satisfactorily.
Numerous researchers have investigated the environmental impact and potential energy savings of different mixtures of recycled concrete using the comparative life cycle assessment (LCA) approach. For example, Colangelo et al. [
30] studied the environmental impact of concrete with recycled aggregates and geopolymer mixtures, concluding that producing concrete with 25% recycled aggregates was the best environmental choice.
In a 2021 study, Mostert and his colleagues [
25] assessed the greenhouse gas emissions associated with the use of recycled aggregates. They used data from a project in Kornbach, Germany, and a building information modeling (BIM) application to illustrate their findings. Their research covered three scenarios related to the life cycle of concrete and examined four different mixtures of varying strengths and exposure classes. The results suggested that a mixture with 43% recycled aggregates could yield up to 37% savings in raw material, though the reductions in climate and water footprints were less significant.
Ghisellini et al. [
27] investigated potential energy savings from various waste management scenarios in the Metropolitan City of Naples. Using the LCA method, they compared concrete made with natural aggregates, recycled aggregates, and green aggregates. Their study indicated that both recycled and green concrete required significantly less energy than their conventional alternatives.
In the same year, [
14] also studied the socio-economic and environmental impact of managing construction and demolition waste in Italy’s Campania Region. Their study suggested the potential for significant carbon savings and job creation with a best practice scenario, though economic challenges could be a barrier.
Lederer et al.’s [
34] study utilized material flow analysis for a case study in Vienna, demonstrating a potential 32% reduction in the annual consumption of construction minerals through waste hierarchy implementation. The study considered various reuse scenarios involving materials such as concrete, brick, asphalt, and gravel.
Zhang et al. [
47] looked at two EU-funded projects, the VEEP and C2CA, to analyze the recovery of end-of-life concrete and predict the future of construction and demolition waste management in the Netherlands. The results pointed to a promising increase in recycling rates from 5% in 2015 to as much as 32% in 2025.
Kioupis et al.’s [
72] research investigated the use of waste from construction and demolition sites, specifically glass and brick, in the production of alkali-activated binders. Their findings suggest that these binders have properties competitive with conventional building materials and are compliant with EU regulations.
Ramírez et al. [
77] explored the possibility of using recycled fibers from mineral wool insulation panels in the production of mortars for coating. Their results indicated that these recycled-fiber mortars showed similar performance to those made with commercial fibers, suggesting potential applications in external coatings.
Superti et al. [
10] examined the entire value chain of insulation materials, identifying the requirements for recycling thermal insulation materials.
Rose et al. [
73] discussed the possibility of using reclaimed timber to make cross-laminated timber, a process that avoids the downcycling common in conventional timber recycling. Their testing suggested that secondary timber could be used effectively in structural applications without significant differences in performance.
Rivero et al. [
68] looked at the environmental impact of plasterboard recycling, using life cycle assessment to examine three potential scenarios. They found that while energy usage did not vary significantly between the scenarios, there was a noticeable decrease in greenhouse gas emissions.
Finally, a 2021 study developed by da Silva et al. [
82] presented a method for recycling polyethylene terephthalate waste into soil-cement brick production. Their results showed that adding up to 30% PET waste to the brick mixture could be a viable option for non-structural applications.
Barriers and drivers in implementation of CE in CDW management
There is a growing interest in the academic community to identify and tackle hurdles in applying circular principles to the management of construction and demolition waste. Enhancing and identifying key processes in CDW management is essential, as it informs future research and assists stakeholders in crafting effective strategies for resource efficiency and sustainability.
Purchase et al. [
1] analyzed components of the circular economy to integrate into construction projects. They categorized the primary challenges into six groups: policy and governance, quality and performance, information, cost/capital, perception and culture, knowledge, education and lack of technology, and permits and specifications.
Concurrently, another study [
48] pointed out logistics as the foremost obstacle to recycling and reuse, followed by cost and time/health and safety regulations.
Han et al. [
2] segmented the barriers to effective CDW management into three categories: technological, policy-related, and human barriers.
Further, researchers like Charef et al. [
63] and Çetin et al. [
83], through a literature review and using the Delphi method, categorized the obstacles under environmental, economic, sociological, organizational, technical, and political challenges.
These various classifications of impediments faced in the execution of CDW management principles were collected and summarized in
Table 7.
The underdeveloped market for secondary materials appears to be a considerable hindrance in all facets of the subject under scrutiny and is frequently highlighted as a pressing need. Concurrently, the call for effective legislative and financial incentives frequently emerges as a challenge. While these obstacles fall into various categories, their interconnections make it more difficult to address them individually. As a result, a comprehensive strategy should be developed by considering these barriers collectively [
2,
35,
52].
On the other hand, researchers have identified certain enablers that could significantly boost initiatives aiming to promote circularity in the construction and demolition (CD) sector. The effectiveness of any sustainability-enhancing initiative in the building sector largely depends on technical viability (like durability), legal enforcement (minimum performance standards set by laws), and the competence and preparedness of the organizations involved (in terms of knowledge, skills, infrastructure, and innovation) [
84]. The drivers identified by the authors of the reviewed studies are illustrated in
Table 8, using a similar categorization approach as used for the barriers.
Prioritizing the barriers and drivers should be tailored to the specific application, considering factors such as national or regional legislation, the degree of circularity incorporated in construction and demolition waste (CDW) management, the availability of natural raw materials, and the waste treatment technology integrated into the waste management system, all of which can vary significantly depending on the local or regional context. The construction sector tends to be traditional in nature, heavily reliant on standards, and primarily driven by economic factors. Moreover, the multitude of stakeholders involved in the CDW value chain contributes to a complex network of responsibilities, characterized by a range of differing decision-making processes [
55].