Review on electronic waste used as construction materials - a scientometric analysis

Abstract Concrete, a widely used building material, should minimize its environmental impact to align with the construction sector’s Sustainable Development Goals. Researchers worldwide are investigating the possibility of e-waste in building materials incorporating various recyclable elements. This paper conducts a thorough review of research on e-waste as a building material. Various E-waste products are used as fine and coarse aggregate replacements in concrete. The study uses a bibliographic approach with the Scopus database to delve into the literature discussing E-waste in construction materials from 2007 to 2022. Data are extracted specifically from Scopus, which identifies 731 papers based on the keyword “Electronic waste used as building materials”. The second step involves scientometric analysis, which focuses on patterns within the articles, such as the most prolific countries, sources, frequently used keywords, and reports containing relevant research. Each research phase contains a summary of the results obtained at various stages. Detailed quantitative and qualitative discussions are also conducted to achieve the three primary goals: a summary of quantitative data, a discussion of the existing application, and identifying future research directions. These findings will be useful for subsequent academic studies on transforming e-waste into building materials. The scientometric review provides a path for researchers from various countries to share new ideas and information while encouraging research collaboration.


Introduction
Sustainable development, which measures the overall environmental, social, and economic needs of current and future generations, is one of the most significant challenges of the 21st century.As a result, the civil construction sector is at a threshold in its efforts to satisfy the "triple bottom line" sustainability criteria.Although associated with environmental implications, the industry consumes 50% of raw materials, produces 40% of industrial waste, and utilizes 30% of the primary energy between 40% and 50% of CO2 emissions (Cheng & Hu, 2022;Kartal, 2022;Sim & Ryu, 2023;Wang et al., 2023;Yelin;You et al., 2023).In addition to degrading ecosystems, the industry may contaminate soil, water, and air.
Concrete is the most widely used material in construction and plays a crucial role in ensuring the health and safety of the world's population, being the second most utilized resource after water (Marimuthu & Ramasamy, 2023;Vishnupriyan & Annadurai, 2023b).Properly made concrete has exceptional durability and flexibility, making it an appropriate engineered material.Until concrete is the most commonly used building material, there needs to be a global strategy to minimize the destruction of natural resources and the environment (Revilla-Cuesta et al., 2022;Z. hai;He et al., 2023;Revilla-Cuesta et al., 2022).Minimizing concrete's environmental impact and the scope of new "green" concrete concepts are essential to bridge the gap between industry growth and planetary boundaries and ensure this construction material's competitiveness (Dang et al., 2023).Given the industry's importance to global economic, social, and environmental development, it may accomplish the UN's Sustainable Development Goals (SDGs).When developing sustainable strategies for the industry, the concrete supply chain may address a range of the 17 SDGs.Many attempts have been made to reuse waste products that are hazardous to the environment, such as ceramic waste, agro-industrial waste, waste coconut shell, recycled aggregate wheat straw ash, waste glass, waste nylon aggregate and peach shell material in the construction industry (Ahmad et al., 2021;Arjomandi et al., 2023;Aslam et al., 2023;Chin et al., 2022;Lee et al., 2021;Mohammed et al., 2022;Revilla-Cuesta, Evangelista, de Brito, Skaf, & Ortega-López, 2022;Zaid et al., 2021Zaid et al., , 2022)).According to a brief review of the literature, studies have attempted to incorporate materials such as locust bean waste ash to make Laticrete blocks, marble dust, rice husk ash, and cement to stabilize expansive soil in subgrade road construction (Fentaw et al., 2021;Ibedu et al., 2023).Utilizing waste and recycled materials, constructing a structure with less material of high durability, and obtaining less impactful construction processes are mostly the main priorities of these strategies (Dang et al., 2023;He et al., 2023;Muñoz et al., 2023;Revilla-Cuesta, Evangelista, de Brito, Skaf, & Manso, 2022;Yan Wang et al., 2023).
The amount of E-waste generated globally was approximately 53.6 million metric tonnes in 2019, and it is projected to reach 74.7 million metric tonnes by 2030, according to the Global E-waste Monitor 2020 report (Forti et al., 2020).This represents a growing environmental and health concern, as e-waste contains hazardous substances that can harm both people and the planet if not managed properly.India is one of the largest generators of electronic waste (E-waste) in the world, with an estimated amount of 3.2 million metric tonnes generated in 2019.However, the country still lacks effective E-waste management and recycling systems, leading to various environmental and health hazards (Forti et al., 2020).The Indian government has implemented regulations and programs to address this issue, but more efforts are needed to improve e-waste management practices and increase public awareness (Joseph, 2007).
In 2019, the world generated 53.6 million metric tonnes of E-waste, according to the Global E-waste Monitor 2020 report (Forti et al., 2020).This represents a 21% increase in E-waste generation in just five years, as the world produced 44.4 million metric tonnes of E-waste in 2014.Asia generated the most E-waste in 2019, with 24.9 million metric tonnes, followed by the Americas (13.1 million metric tonnes) and Europe (12 million metric tonnes).The per capita E-waste generation was highest in Oceania (16.2 kg/person) and Europe (16.2kg/person), followed by the Americas (13.3 kg/person) and Asia (5.6 kg/person).The United Nations University (UNU) estimated that the value of recoverable materials in global e-waste was approximately $57 billion in 2019.However, only 17.4% of this E-waste was recycled through appropriate channels, with the rest either ending up in landfills and incinerators or being informally recycled.
E-waste can be used as a partial replacement for traditional materials such as sand and aggregates in concrete production (Balasubramanian et al., 2016b;Bharani et al., 2020;Dhanraj & Selvamony, 2021;Prasanna & Rao, 2014).This can help to reduce the environmental impact of e-waste disposal while also addressing the demand for construction materials (Priyan et al., 2023;Vishnupriyan & Annadurai, 2023a, 2023b).Research has shown that incorporating E-waste in concrete can improve its mechanical properties, such as compressive strength and durability, while also reducing its carbon footprint (Balasubramanian et al., 2016a;Alagusankareswari et al., 2016;Masuduzzaman et al., 2018;He et al., 2023).However, the use of e-waste in concrete is still relatively new, and there are concerns about the potential leaching of hazardous materials from e-waste into the environment.As a result, additional research is needed to fully understand the possible advantages and hazards of using e-waste in concrete, as well as to develop appropriate guidelines and standards for its safe use in construction.
A systematic review is a comprehensive and structured approach to reviewing the literature on a specific topic (Aguinis et al., 2023;Carvalho & Alves, 2023;Jin et al., 2019a;Lorenz-Spreen et al., 2022;Mariani et al., 2023).A systematic review of e-waste could involve identifying, selecting, and critically appraising all relevant studies on e-waste to synthesize the available evidence on this topic.Such a review could cover a wide range of issues related to e-waste, including its sources and quantities, environmental and health impacts, management and disposal practices, recycling and recovery technologies, and policy and regulatory frameworks.The findings of a systematic review on e-waste could provide valuable insights for policymakers, industry stakeholders, and researchers and help to identify key research gaps and priorities for future studies in this field.There are several examples of systematic reviews on e-waste, and more are likely to be conducted in the future as the field continues to evolve.
The science mapping approach was used to conduct this review of the literature on the topic of e-waste material in concrete.The purposes of this study comprise analysing influential journals, keywords, and countries using a science mapping methodology, examining current mainstream research topics in sustainable construction, and recommending a research framework that will direct future research and academic work (Chan & Wu, 2005;Chen, 2006;Ganbat et al., 2018;Huang et al., 2022).In this study, a scientometric examination of bibliometric data pertaining to the use of electronic wastes (E-waste) as construction materials was conducted.Utilizing scientometric analysis, the inherent limitations of traditional manual reviews were examined.The study focused on several aspects, including the identification of sources with the highest number of articles, the co-occurrence of keywords, author collaboration, the most frequently cited articles, and the regions actively involved in utilizing e-waste as building materials.This study's quantitative and graphical representation of participating countries and researchers can also help academics build collaborative initiatives and disseminate new ideas and methods.This scientometric review uses the science mapping approach to analyse the specific domain of e-waste and to make recommendations for additional research into specific subthemes within this domain.

Scientometric analysis
Utilizing the text-mining application VOS Viewer, the assessment utilized a scientometric analysis technique (Darko et al., 2019a;Ganasen et al., 2023b;Li et al., 2021).There is additional background information available on the scientometric analysis.VOS Viewer generates distance-based network visualizations in which the distances between nodes indicate the degree of proximity between them.It is appropriate for imagining larger networks thanks to its text mining-specific capabilities (Ganasen et al., 2023a).A bibliometric search was performed to collect a sample of literature on e-waste material in concrete, which was then imported into VOS Viewer for scientometric assessment.This analysis enabled the identification of influential publishers, keywords, researchers, and articles in the field (Zhang et al., 2020;Marvuglia et al., 2020;Li et al., 2020a;Vlachokostas et al., 2021;Japec et al., 2015).

Need for a systematic review of e-waste in construction materials
A systematic review of the use of e-waste in construction materials could help to provide a comprehensive understanding of the current state of knowledge in this area and identify any gaps or areas for future research.Some potential benefits of conducting a systematic review could include the following: • Synthesizing existing evidence: A systematic review would allow for the synthesis of existing evidence on the use of e-waste in construction materials, providing a comprehensive overview of the research conducted in this area.
• Identifying knowledge gaps: The review could help identify gaps or limitations in the existing research, highlighting areas where further investigation is needed to fully understand the potential benefits and drawbacks of using E-waste in construction materials.
• Supporting evidence-based decision-making: The findings of the systematic review could be used to inform evidence-based decision-making around the usage of e-waste in building materials, guiding policymakers, industry stakeholders, and researchers.
• Enhancing research quality: A systematic review would require a rigorous and transparent methodology, which could help to enhance the quality of research in this area and provide a foundation for future studies.

Research methodology
This study employs a "holistic review method" to achieve its research objectives.The holistic approach typically includes quantitative and qualitative reviews (Yin et al., 2019).This method eliminates biased conclusions and subjective judgment and provides a comprehensive understanding of the research domain and trends (Zou et al., 2014).As quantitative methods, bibliometric and scientometric analyses were chosen for this work.Evaluation of the papers published in the E-waste concrete field over the past decade is conducted in two stages.

Bibliometric search
Even though conventional literature reviews fall flat to offer sufficient direction, bibliometric assessments have a significant impact in assisting scholars in charting a path forward (Japec et al., 2015).Bibliometric analysis is an effective method for gaining a thorough understanding of a particular field of research, and it offers added understanding into previously unexplored or underutilized topics (Fahimnia et al., 2015).
• Database: Scopus is widely used for bibliometric studies due to its reputation for producing highquality records (Zeng & Chini, 2017).Accordingly, Scopus was selected as the research paper database.
• Keywords: It is challenging to cover all potential research terms in a single study (Falagas et al., 2008).As a result, based on the discussion of previous studies and the aims of the current work (Geng et al., 2017, Darko et al., 2019b), the following keywords were chosen: ("Electronic waste concrete" OR "E-waste concrete" OR "cathode ray tube concrete" OR "CRT concrete" OR "E-Waste").
• Timespan: -The study period was fixed to last 15 years, from 2007 to 2022.Furthermore, the assessments in the introduction demonstrate that the assessments of E-waste concrete in the last 10 years are insufficient.The initial search yielded 1554 documents.The earlier literature samples are further screened and refined using the three steps outlined to eliminate articles with incoherent research objects, i.e., to examine e-waste in concrete.Multiple studies on e-waste management were omitted.Following a three-step examination, 731 research articles were selected as samples of the previous research for the subsequent examination.The study's workflow is depicted in Figure 1, which depicts the overall structure.

Scientometric analysis
Based on large academic datasets, a bibliometric analysis is an approach for charting the development of knowledge in a field and gauging the impact of previous studies.Scientometric analysis was developed to aid in identifying objectivity issues in literature reviews (Hammersley, 2001) for the e-waste concrete field.The scientometric method involves co-occurrence assessment of keywords, publishers, and regions (Chen, 2017;Darko et al., 2019b).
Scientometric mapping includes knowledge mining and visualization, valuable mining data, and investigating trends from the crafted visual network (Li et al., 2020b).The analysis and time-series visualization of characteristics and changes in a singular entity of literature could be performed using various scientometric tools (Cobo et al., 2011).VOS Viewer and R-Studio were used for scientometric analysis.In this study, the scientometric analysis was conducted using VOS Viewer version 1.6.18as suitable for large-scale network visualization and capable of providing text mining data outcomes (Van Eck & Waltman, 2014a).

Source analysis
Analysing the influence of sources in a keyword field enables readers to obtain the most accurate data It is possible that their work is most likely accepted for publication (Darko et al., 2019b;Jin et al., 2019a).This research counted the highly influential publications dedicated to studying E-waste concrete, summarizing and illustrating the sources used to collect the data.The outcomes are depicted in Figure 2 and Table 1.In 731 data are, during VOS Viewer.During an analysis, set 5 as the minimum number of documents in sources.Among the 98 identified, 7 sources meet and satisfy these thresholds.Figure 2 shows a visualization network.quantitative measurements of journal influence.Total citations correlate with the number of articles among the seven assessment indicators, indicating the extent of cumulative research (Jin et al., 2019).Based on this, average normal citations dispel the idea that because older papers have been around for a longer time, they receive more citations than more recent ones (Van Eck & Waltman, 2014a).As a result, there are two leading indicators used in this study's analysis: the number of papers and the average normal citations (Jin et al., 2019), and this is the basis for sorting the Table .The two factors are relatively independent, meaning that productive journals have a high normalized average citations per article (Jin et al., 2019b).
According to Table 1, CBM, JCP, and materials were most influential in E-waste concrete research.Although material today: proceedings have published many papers related to e-waste concrete, they have a low average citation, indicating that the average citation of material per year in proceedings journals is not the most influential.The journal article activity is represented by the average publication year.Recently, most studies have been published in the JCP, Materials, and Journal of Building Engineering of E-waste concrete research.

Analysis of article regions
The lowest number of articles was established at 5, and 11 out of 50 nations met this threshold.Figure 2 and Table 2 depict the results of E-waste concrete research conducted in productive and influential countries.Figure 3 and Table 2 indicate that India, China, and Malaysia publish the most research papers and their aid in the research.Their relations suggest that they actively construct a global collaboration network.The two top e-waste-producing countries (China and India) are trying to find an alternative solution for managing E-waste generation by introducing it in concrete.According to Table 2, the measurement reveals that Pakistan, Australia, and Iraq have had the most significant impact on E-waste concrete research each year, followed by China, the United States, and Malaysia.Although most of the literature papers' sources are from developing nations and developing nations exert a more significant influence, E-waste concrete-related research has been conducted.This is because most of the developed concrete exports its E-waste to developing countries.

Keywords analysis
Keywords are the primary significance of a paper, condensing the subjects of interest within a particular area (Jin et al., 2019a;Su & Lee, 2010;Van Eck & Waltman, 2014b).The least number of occurrences was established at 20 in VOSViewer using "Author Keywords" to map the link; initially, 24 of the 1797 keywords satisfied the threshold.Furthermore, similar keywords were integrated, such as "Electronic waste concrete" versus "E-waste concrete".Finally, the 21 keywords were examined in Figure 4 and Table 3. Mechanical properties, e-waste glass, cathode ray tubes, and sustainable development receive high scores based on their average normal citations, as shown in Table 3.This suggests that influential studies focus on the application and development prospects of E-waste concrete.
The average publication year indicates how recently a given keyword has been studied for E-waste concrete.The node size in Figure 4 signifies the number of times the keywords appear,    and the connection's length and breadth show how closely related the two keywords are to one another.According to Figure 4, the most common keywords used in past research on E-waste concrete included "electronic waste", "compressive strength", "recycling", and "waste disposal".Different node colours correspond to distinct keyword clusters.Keywords were divided into two clusters, green and red, in Figure 4.These keywords and mapping topics implicitly or explicitly implicated the four pillars of philosophy: axiology, ontology, epistemology, and methodology.
Figure 5 depicts the top 10 index keywords or keywords-plus utilized in E-waste concrete in documents.In E-waste, concrete documents used in the indexed keyword "E-waste" have a 64% contribution in the top 10 keywords.The index keyword "Compressive strength" contributes 55%, followed by "Recycling" at 51%.The index keyword "Concrete" contributes 40%, followed by index keywords such as "mechanical properties" and "Sustainability," which contributed 25% and 24% of the top 10 keywords, respectively.Similarly, index keywords such as "Electronic Waste" and "Flexural Strength" contributed 19%, followed by keywords such as "Durability" and "Waste Management", which contributed 18% in the top searches.
The topic dendrogram in Figure 6 illustrates the conceptual organization of the keywords used and, consequently, the essence of the most researched topics in the field of e-waste.The dendrogram is a branching diagram that starts with a single point at the top and then branches out into multiple lines or "branches."Each branch represents a different group of keywords that are related to each other based on their similarity.The closer the branches are to each other, the more similar the keywords are.Based on a factorial analysis, the topic dendrogram was created using the following parameters: Multiple correspondence analysis was used to create the dendrogram; the number of terms was set to 18, and the program was given free rein to decide how many clusters to create.Two groups of topics were created from the topics.The top searched keywords used for finding research articles related to e-waste can be arranged in a hierarchical structure based on their relationships.Here, "E-waste research" related keywords, which could then be divided into subcategories such as "Compressive strength," "Cement," "Concrete mixtures," and "Tensile Strength".Each subcategory could then be further divided into more specific keywords such as "aggregate," "E-waste," "waste disposal," "and recycling," As the dendrogram branches out, it becomes more specific and granular, allowing researchers to hone in on the exact keywords that are most relevant to their search.
In general, previous research has validated the fundamental ideas underlying the use of e-waste as a construction material.In this context, one group of relevant keywords relates to the mechanical strength and material properties of e-waste.Another group comprises recurring topics, such as using e-waste in construction projects.By employing this method of filtering, researchers can streamline their searches by ignoring irrelevant articles and focusing on those that are most relevant to their work.

Most cited top 10 documents
E-waste is a growing concern as electronic devices become more ubiquitous daily.Proper E-waste disposal is critical to reducing the environmental impact and well-being risks associated with these materials.As a result, there has been significant research in this field over the years.Using the keywords "E-waste," 731 articles were found in the Scopus database.Table 4 shows the top 10 globally cited articles based on total citations (TC), TC per year, normalized TC (Norm.TC), and reference counts (Ref.)Here are the top 10 most cited research articles on e-waste, according to the Scopus database.

Trend analysis
In recent decades, e-waste has spawned relevant literary works as a sustainable alternative building material.There are numerous other publications and attempts at research in this area beyond articles and technical documents.Figure 7 depicts the most commonly used construction materials, including sand, cement, concrete, and e-waste.Sustainable buildings rely heavily on technological advancements.As an alternative to cement and concrete, many studies have been conducted, with a recent focus on using e-waste as a substitute for both fine and coarse aggregates.E-waste, concrete, recycling, and compressive strength are just some of the 731 keyword entries found between 2015 and 2021.
The trend topics were generated solely based on papers that were published between 2015 and 2021.Additional graphical parameters pertain to the utilization of the author's keywords field, wherein a minimum word frequency of five is applied, and the number of words to be evaluated per year is established at five.The main keywords utilized in each year can be observed from Figure 7 under the given circumstances.The lines depicted in the graph correspond to the chronological sequence of years during which the aforementioned word was utilized.The most frequently occurring instance of the word, along with the year in which it was utilized, is visually   emphasized by a bubble located on the corresponding line.The magnitude of the bubbles corresponds to the frequency of utilization for each term, whereby the larger the bubble is, the greater the frequency of use.The findings demonstrate a resemblance to the outcomes presented in the VOS viewer.
The current trend in e-waste discourse indicates a shift in the strategies employed to address the issue.During the initial phase of the time period, the prevalent keywords suggest that the majority of the subjects discussed pertained to the utilization of electronic waste in the context of concrete.Prior to 2017, the most frequently utilized term was "electronic waste."Following 2017, it appears that there has been a shift in the frequency of certain terms utilized within the field.Specifically, there has been an increase in the usage of terminology such as "fly ash," "compressive strength," "flexural strength," "mechanical properties," "recycling," and "green concrete."The aforementioned factors collectively signify a shift that has occurred within the past five years, wherein e-waste has transitioned from being viewed solely as a replacement for aggregate to being utilized as a construction material.This shift has been motivated by the desire to mitigate the environmental impact of buildings and the construction industry at large.That graph after 2017 makes it clear that the research was primarily targeted at enhancing the mechanical properties of e-waste concrete by using additives such as fly ash.
The incorporation of electronic waste materials in the construction sector has been found to mitigate environmental risks and emissions associated with waste disposal methods such as storage and incineration.This approach also prevents the overaccumulation of waste in sanitary landfills, thereby enhancing the overall environmental conditions.Numerous scholars have utilized electronic waste as construction materials across diverse domains.Overall, the use of electronic waste in the construction sector has proven to be a sustainable and environmentally friendly solution that not only addresses the issue of waste disposal but also offers potential economic benefits.As technology continues to advance, it is important to continue exploring innovative ways to incorporate electronic waste into construction materials and practices.

Conclusions
The purpose of this scientometric literature review was to analyse the state of knowledge concerning the use of e-waste in building materials.The VOS Viewer was then used to evaluate the records from the 731 identified articles through the Scopus search.These results are based on that study: • Fewer than 50 countries produce at least 11 E-waste in construction materials research documents, according to an assessment of the contributions of the leading nations.Based on citations, India, China, and Malaysia may be ranked in the top three.
• An evaluation of sources, evaluating the top sources according to their input to E-waste research, revealed that only seven sources produced at least five documents.Note that "Construction and Building Material," "Journal of Cleaner Production," and "materials" are the top three sources.
• "Electronic waste", "compressive strength," "recycling," and "waste disposal" are the most frequently occurring terms in the research on e-waste used in construction materials.Research has been conducted to improve the mechanical and durability properties of E-waste concrete, specifically to manage brittleness and stop the expansion of cracks.
• Building materials containing e-waste have been utilized in various engineering applications, such as precast members, retaining walls, road sidewalks, and bridges.
• This study helps research sources find an article and country for collaboration and keywords for further studies in e-waste used in building materials.

Future direction
The use of e-waste in building materials is a promising area for research and development, and some future directions that could be explored include the following: Several key research areas are involved in an integrated approach to incorporating electronic waste (E-waste) as building materials.First, material characterization is critical, emphasizing the importance of conducting in-depth investigations into e-waste materials to evaluate their suitability for construction applications and to recognize any associated health and environmental risks.Second, research efforts should be focused on discovering improved techniques for the processing and disposal of e-waste.This would not only aid in the extraction of valuable building materials but also help to reduce waste generation and the release of dangerous substances.Furthermore, it is critical to develop standards and guidelines for the safe and effective use of E-waste in building materials.These guidelines help ensure that such materials meet performance, health, and safety standards.Life cycle assessment investigations should be performed to evaluate the effects of using E-waste as a construction material to comprehensively assess the environmental impact.These studies are critical to discovering potential trade-offs or unintended consequences of this strategy.Finally, the commercial feasibility of using E-waste as a building material warrants careful consideration.The research should concentrate on determining the economic feasibility, which includes the costs of processing and treating E-waste and the potential benefits of using these materials in construction.By focusing on these research areas, society may move towards a more environmentally friendly and accountable utilization of e-waste in the construction industry, addressing environmental and economic concerns.

Figure 2
Figure 2 indicates that Materials today: Proceeds, Construction and Building Materials (CBM) and Journal of Cleaner Production (JCP) published the maximum number of papers.These journals contribute significantly to E-waste concrete research.Table 1 summarizes seven major

Figure
Figure 2. Visualization of sources on E-waste concrete.

Figure 3 .
Figure 3. Analysis of regions active in E-waste concrete research.

Figure 4 .
Figure 4. Keyword mapping in the e-waste concrete domain.

Figure 5 .
Figure 5. Tree diagram of most searched keywords on e-waste concrete.

Figure
Figure 6.Dendrogram of the most searched keywords on e-waste concrete.
Table 1 summarizes seven major

Table 1 . Analysing article journal sources quantitatively for concrete research on E-waste
aNorm:Citation ¼ Total number of citations Average citation peryear bAvg:Norm:Citation ¼