*Review* **Waste Glass Utilization in Cement-Based Materials for Sustainable Construction: A Review**

**Di Qin 1, Yidan Hu <sup>1</sup> and Xuemei Li 2,\***


**Abstract:** The construction industry has a significant environmental impact, contributing considerably to CO2 emissions, natural resource depletion, and energy consumption. The construction industry is currently trending towards using alternative construction materials in place of natural materials and cement, thereby reducing the environmental impact and promoting sustainability. Two approaches have been used in this review: scientometric analysis and a comprehensive manual review on the waste glass (WG) utilization in cement-based materials (CBMs) as a sustainable approach. Scientometric analysis is conducted to find out the current research trend from available bibliometric data and to identify the relevant publication fields, sources with the most publications, the most frequently used keywords, the most cited articles and authors, and the countries that have made the most significant contribution to the field of WG utilization in CBMs. The effect of WG on the mechanical properties of CBMs was found to be inconsistent in the literature. The inconsistent effects of WG impede its acceptance in the construction sector. This study intends to shed light on the arguments and tries to explain the opposing perspectives. This article summarizes the findings of various research groups and recommends new viewpoints based on the assessment of fundamental processes. The effect of utilizing WG on fresh and hardened properties of CBMs, including workability, compressive strength, split-tensile strength, and flexural strength, are reviewed. Furthermore, the microstructure and durability of composites containing WG are investigated. Different limitations associated with WG use in CBMs and their possible solution are reported. This study will assist researchers in identifying gaps in the present research. Additionally, the scientometric review will enable researchers from diverse regions to exchange novel ideas and technologies, collaborate on research, and form joint ventures.

**Keywords:** cement-based materials; waste glass; sustainable construction; mechanical properties; durability

## **1. Introduction**

Sustainability trends have accelerated recently as a result of resource constraints, resulting in an increased number of emerging issues from managerial, strategic, and operational perspectives. Additionally, the construction sector significantly contributes to society's requirements by improving people's quality of life [1–3]. Despite this, this industry generates between 45 and 65% of waste disposed of in landfills, accounting for 35% of global CO2 emissions. Additionally, the construction industry and its related activities generate substantial amounts of harmful emissions, accounting for nearly 30% of global greenhouse gas emissions resulting from construction operations, with transportation and processing of construction materials accounting for 18% of these emissions [4]. The value of sustainability research in the field of civil construction is self-evident. In this regard, firms are increasingly aware that ensuring a competitive advantage is contingent on more than just client satisfaction based on low costs and the quality of the product or service provided. Clients expect businesses to be ethical, environmentally conscious, and socially

**Citation:** Qin, D.; Hu, Y.; Li, X. Waste Glass Utilization in Cement-Based Materials for Sustainable Construction: A Review. *Crystals* **2021**, *11*, 710. https://doi.org/ 10.3390/cryst11060710

Academic Editors: Piotr Smarzewski and Adam Stolarski

Received: 8 June 2021 Accepted: 17 June 2021 Published: 21 June 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

responsible [5]. As a result, sustainability in construction must be seriously considered. Researchers have concentrated on a variety of factors in order to achieve construction sustainability. One of them is the utilization of waste materials in construction materials.

Several processes, including mining, manufacturing, agricultural production, electricity generation, iron and steel metallurgy, and electronic goods, generate massive amounts of solid waste. Many hazardous solid wastes are flammable, chemically reactive, incendiary, corrosive, and infectious, and their discharge and disposal have resulted in large financial losses [6,7]. As a result, solid waste recycling or reuse in construction materials would be preferable [8]. Cement-based materials (CBMs) are extensively used construction materials [9–12]. Researchers have used various approaches to enhance the performance of CBMs [13–16]. Waste materials can be used in concrete as an aggregate substitute [17–22], as fibers for reinforcement [23–28], as well as a cement substitute [29–35] to improve CBMs' performance. As a result of the reduced cement consumption, natural resources can be conserved, and CO2 emissions can be reduced. Furthermore, it has been discovered that incorporating waste materials into CBMs improves their mechanical performance [36–38]. Each year, tens of millions of tons of waste glass (WG) are produced in the United States [39], with a huge quantity of WG being disposed of in landfills. Although many cities are producing more WG at a growing rate, landfill space is becoming scarce, particularly in major cities. Glass is chemically stable as compared to certain forms of solid waste, such as plastic and wood. Glass that has been buried in soil for a long time is non-biodegradable [40]. Furthermore, certain glass, for example, cathode ray tube (CRT) glass, holds toxic elements such as mercury, cadmium, lead, and beryllium, polluting subsurface soil and water [41]. China produces CRT glass at a rate of more than 43 million tons per year [42], posing a major environmental threat and endangering public health. Glass production requires a considerable amount of energy as silica must be melted at an elevated temperature for hours [43]. For container glass, the temperature is kept at 1500 ◦C for 24 and 72 h for plate glass [44]. Producing 1 kg of plate glass utilizes approximately 17 MJ (mega-joule) of fossil fuel energy and emits approximately 0.6 kg of CO2 [45]. In Europe, annual energy consumption for glass manufacturing exceeds 350 PJ (peta-joule), accounting for approximately 20% of overall industrial energy utilization [45]. Thus, recycling WG effectively is generating increasing interest worldwide. Recycling glass for use in the manufacture of glass products is a popular method of reusing WG. However, recycling is a complicated process. To produce glass plates and containers, WG ought to be cleaned, sorted, and melted [46]. Another way to recycle WG is to use it to make construction materials. WG can be crushed and mixed with cement and aggregates in CBMs to partially replace cement/aggregates [21,47–51]. The use of WG in CBMs has several benefits. First, the WG utilized in CBMs does not need to be melted, so minimizing the energy requirement. Second, WG management is significantly simplified. For example, glass cleaning and sorting are not required. Third, WG consumption will be high due to the extensive use of CBMs in construction. Fourth, toxic elements in glass can be locked and solidified within CBMs. Present research indicates that recycling WG in CBMs is a better approach [47,48]. Thus, the use of WG in construction materials as an aggregate replacement will contribute to save natural resources and solve waste management problems. Its use as a cement replacement will help to reduce the cement demand and ultimately decrease CO2 emission.

As a result, there is a need to investigate sustainability in construction, which has been discussed in this paper. Manual reviews are insufficient for building a deep and consistent relationship between different literature sections. Scientific mapping and network visualization of bibliographic coupling, co-citations, and co-occurrence are currently among the most difficult parts of modern research. A scientometric review can deal with large amounts of data without adding to the complexity of responding to the fundamental limitations of earlier manual evaluations. To solve the fundamental drawbacks of traditional reviews, scientometric analysis is used in conjunction with traditional reviews in this study. More specifically, a thorough examination of the keywords co-occurrence, co-authorship by researchers, bibliographic coupling of sources, articles, and countries actively contributing

to the subject of the utilization of WG in concrete for sustainable construction is conducted. The effect of WG on the mechanical properties (MPs), microstructure, and durability of CBMs are reviewed. Various limitations associated with WG utilization are identified, and their possible solution is detailed. In the current study, scientometric analysis is used in conjunction with an in-depth discussion to achieve the following objectives: (1) To identify the most relevant publishing field, publication sources, most frequently used keywords, most cited authors and works, and nations with the greatest influence in the field of WG utilization for sustainability in construction. (2) To examine the current level of research and its focus on a variety of elements throughout the last two decades. (3) To identify research gaps so that future research can be directed in the proper direction.

#### **2. Research Significance**

In recent decades, a substantial study has been done to explore the elements that contribute to sustainability in construction, and some useful results have been reached. Review studies were also conducted; however, these were primarily manual reviews. This study is based on scientometric analysis, as well as an in-depth discussion on WG utilization in CBMs as a sustainable approach. The reason for selecting WG from the various waste materials is because it is non-biodegradable and contains toxic chemicals that have a greater detrimental impact on the environment if disposed of in landfills. Researchers from various locations may benefit from the graphical depiction based on a scientometric evaluation in forging research alliances, forming joint ventures, and sharing breakthrough technologies and ideas as a result of this research. Furthermore, the advantages associated with WG utilization in construction are described. Specifically, the impact of WG on the mechanical performance of CBMs and its sustainability aspects are reviewed. Different restrictions related to the use of WG are also discussed, as well as possible remedies. Finally, possible future studies are recommended.

#### **3. Methodology**

This study employed two approaches: a scientometric analysis review [52–55] and an in-depth discussion on WG utilization in construction materials. The primary reason for instituting a scientometric review method is that subjective analyses of civil engineering studies by researchers have been shown to be prone to error. Scientometrics, by itself, provides a more rational and less skewed outcome, as it is not biased by any individual's perspective [56–58]. This study examines and articulates findings spanning two decades. Maps and connections between bibliometric data are used to quantify research progress in this report, resulting in a quantitative assessment.

Numerous publications have been written in the area under study, and it is critical to locate the most accurate database. According to Aghaei et al. [59], the two most effective, comprehensive, and objective databases for conducting literature searches are Web of Science and Scopus. Scopus has a broader coverage and more up-to-date bibliometric data than Web of Science [59–61]. Scopus was used to compile the bibliometric data for the current analysis on the utilization of WG for sustainable construction. The searched keyword in Scopus was "waste glass in concrete", which resulted in 1488 documents. Options for data refinement were used to weed out irrelevant publications. From the "document type", only "article" and "review" were selected. The "source type" field was kept to "journal", while the "language" field was "English". The "publication year" was limited from 2001 to 2021. The "subject area" was kept "Engineering, Material Science, and Environmental Science". After applying these limiting filters, the resulting documents were 737. Researchers from a variety of fields have previously conducted research using similar methods [62–64]. Scientometric reviews make use of science visualization, a technique developed by scholars for analyzing bibliometric data for a variety of purposes [65]. It describes the difficulties researchers face when conducting manual reviews and also establishes a connection between sources, keywords, authors, articles, and countries within a particular research area [66]. Scopus data were saved in the Comma Separated Values (CSV) format for subsequent

analysis with an appropriate software tool. The science mapping and visualization were created using the software tool VOSviewer (version: 1.6.16). VOSviewer is a freely available visualization application that is widely used in a variety of fields and comes highly recommended in the literature [67–71]. Hence, the VOSviewer was used to accomplish the current study's objectives. The analysis was conducted in VOSviewer, with the "type of data" set to "create a map from bibliographic data" and the "data source" set to "read data from bibliographic database files". The CSV file downloaded from Scopus was imported into VOSviewer and analyzed in a few simple steps while ensuring data consistency and reliability. As part of the science mapping review, the sources of documents, keyword cooccurrence, citation network, co-authorship, articles, bibliometric overlapping, and country contributions were analyzed. Additionally, the cumulative number of citations to articles was tallied. Additionally, the connections between authors, publications, and countries were charted. Maps were used to visualize various parameters, their relationships, and co-occurrence, while tables were used to summarize their quantitative values. Additionally, the keywords were thoroughly reviewed and summarized in the discussion section in order to develop the major research themes. The sequence of the scientometric analysis is depicted in Figure 1.

**Figure 1.** Sequence of scientometric analysis. CSV: comma separated values.

#### **4. Results and Discussion on Scientometric Analysis**

#### *4.1. Subject Area and Annual Publication Pattern of Articles*

The Scopus analyzer was used to search the Scopus database in order to determine the most significant research areas. The analysis revealed that the top three fields based on the number of documents were determined to be Engineering, Materials Science, and Environmental Science, containing 34.7%, 21.9%, and 16.0% of the total documents, respectively, as illustrated in Figure 2. These fields account for around 72.6% of the total number of documents searched in the Scopus database. Both journal articles and review articles were compared for the overall documents. Journal articles contributed 90.9%, and review articles contributed 9.1%, respectively. Figure 3 depicts the annual publication pattern in the current study field from 2001 to 2021. A gradual increase in the number of publications

on the utilization of WG in concrete has been observed up to 2016. However, a remarkable increase was observed in the last 5 years. It is fascinating to discover that scholars are now focusing their studies on sustainable construction methods.

**Figure 2.** Subject area of articles.

**Figure 3.** Annual publication pattern.

#### *4.2. Sources Mapping*

Mapping sources enables the analysis of development and innovation to be visualized. These sources make data available within the confines of predefined, unique constraints. By initializing the mapping of research origins, it is possible to apply the research pattern sequentially in the analysis area. This analysis was conducted in VOS viewer using Scopus bibliometric data. The "type of analysis" was selected to be "bibliographic coupling," and the "unit of analysis" was selected to be "sources". A source's minimum document

count was set at 10, and 10 of the 256 sources met this criterion. Table 1 lists the leading sources/journals that publish at least 10 documents containing data on WG in concrete for sustainable development, along with their citations and total link strength. Based on the number of documents, the top 3 journals are construction and building materials, the journal of cleaner production, and the international journal of civil engineering and technology, containing 112, 56, and 25 documents, respectively. The highest citations are of construction and building materials (3989), followed by cement and concrete research (1935) and journal of cleaner production (1878). Figure 4 illustrates the annual publication trend of sources and their scientific mapping. This data was gathered as part of the process of establishing a network of research sources. It is worth noting here that this type of research would lay the groundwork for upcoming scientometric reviews in the current study field. Additionally, previous manual reviews lacked sufficient detail regarding science mapping. Figure 4a depicts the yearly publication trend of the top journals. The contribution of resources, recycling and conservation is from 2002. While the contribution of construction and building materials, journal of cleaner production, and materials is from 2007, 2009, and 2016, respectively, in the current study field. It can be seen that up to 2016, the number of publications was insignificant, while an abrupt hike in the last 5 years was observed especially for construction and building materials. The network visualization of journals containing at least 10 documents has been displayed in Figure 4b. The size of the frame in the figure corresponds to the journal's contribution in terms of citation and documents count; a larger frame size indicates a higher contribution. For example, construction and building materials has a bigger frame size, indicating that this journal has the greatest influence in the current study area relative to the other. Additionally, frames (sources) with identical colors display clusters of related frames developed through VOSviewer analysis. For instance, the red color indicates a cluster containing construction and building materials, journal of cleaner production, materials, journal of building engineering, and applied sciences (Switzerland). Clusters are formed based on the scope of research outlets or their co-citations. [72]. The number of co-citations in the articles in the current study area is indicated by the connection links between the research sources. Additionally, the link strength indicates the number of mutually cited references between two journals. For instance, the journal of cleaner production (total link strength: 9941) contained the greatest number of references to other research sources. Closely spaced frames (sources) in a cluster have stronger connections than those that are further apart. For example, the construction and building materials is more connected with cement and concrete composites than it is with other sources.


(**b**)

**Figure 4.** Sources of research articles: (**a**) yearly publication trend; (**b**) network visualization.

#### *4.3. Keywords Mapping*

Keywords are essential research materials because they identify and represent the research domain's fundamental field [73]. For that analysis, the "type of analysis" was chosen as "co-occurrence" and "unit of analysis" as "all keywords". The minimum number of occurrence of a keyword was kept to 20. These constraints indicated that only

100 keywords from 5576 satisfied the criteria. Table 2 lists the top 20 keywords having the most occurrence in the research articles used in the present study field. According to the researcher's study, the most commonly occurring keywords include glass, compressive strength, concretes, recycling, and concrete, making the top 5 mostly occurred keywords. Figure 5 illustrates the co-occurrence of keywords networks, their visualization, their connections to one another, and the density associated with their correlation frequency. The size of the keyword node in Figure 5a indicates its frequency, whereas its location indicates its co-occurrence in publications. Additionally, the visualization demonstrates that the aforementioned keywords have bigger nodes than the others, indicating that these are the most important keywords in the study of WG utilization in concrete for sustainable construction. Clusters of keywords have been colored differently in the network to indicate their co-occurrence in various publications. A total of five clusters were observed, represented by green, red, blue, yellow, and purple. For example, a cluster represented by green color contains glass, silica, cements, durability, silica fume, cement replacement, concrete mixtures, etc. As illustrated in Figure 5b, the density concentration of keywords is denoted by distinct colors. Red, yellow, green, and blue are the colors in ascending order of density. For example, glass, compressive strength, and concretes have red marks in the density visualization, indicating a higher density. This finding will aid writers in the future when selecting keywords to make it easier to locate published data in a particular domain. Figure 6 illustrates the connections of glass (Figure 6a), waste management (Figure 6b), and recycling (Figure 6c) with other keywords. The connection network demonstrates that glass and recycling have a sizeable impact on waste management. Thus, recycling WG would reduce the burden from waste management authorities.


**Table 2.** Top 20 most occurred keywords.

(**a**)

(**b**)

**Figure 5.** Mapping of keywords: (**a**) co-occurrence visualization; (**b**) density visualization.

(**b**)

**Figure 6.** *Cont.*

(**c**)

**Figure 6.** Connection of a keyword with others: (**a**) glass; (**b**) waste management; (**c**) recycling.

#### *4.4. Co-Authorship Mapping*

Citation counts indicate a researcher's influence in a particular field [74]. In the VOSviewer, "co-authorship" was selected as the "type of analysis", while "authors" were chosen as the "unit of analysis". The minimum number of documents required for an author was kept at 5, which resulted in 20 of the 2077 authors meeting the constraints. The top 20 authors in the field of WG in concrete for sustainable growth with the most documents and citations are listed in Table 3, according to the data retrieved from the Scopus database. The average citation count was calculated by dividing the total number of citations by the number of publications by each author. Poon C.S. was the author of the most publications (16), while Arulrajah A. was the author of the most citations (656). It will be difficult to independently assess a researcher's effectiveness. However, the author's rating will be determined by comparing all variables individually or in conjunction with one another. For instance, if the total number of documents is compared, the top three authors are Poon C.S with 16, Arulrajah A. with 13, and Tagnit-Hamou A. with 12 publications. Alternatively, if the number of citations is compared, the author's ranking would be Arulrajah A. with 656, Shi C. with 624, and Poon C.S. with 567 citations. Additionally, when comparing average citations, the authors are ranked as follows: Shi C. with 125, Poon C.-S. with 75, and Ling T.-C. with 54 average citations. Figure 7 illustrates the visualization of authors with a minimum of 5 documents and the linkage of the most prominent author. Of the 20 authors, only 4 have been linked. It was observed that authors from different regions are not connected to each other based on citations in the field of WG utilization in concrete.



18

**Figure 7.** Visualization of co-authorship; (**a**) authors with minimum five documents; (**b**) connected authors.

#### *4.5. Articles Mapping*

The number of citations a research article receives indicates its impact on a particular field of study. Articles with a high citation count will be considered a landmark in the history of science. To analyze document citations, the "type of analysis" was set to "bibliographic coupling" and the "unit of analysis" to "document" in the VOSviewer. A document's minimum citation count was set to 50, and 102 of the 737 records adhered to these boundary requirements. The top 20 highly cited research articles, their authors, and the year of publication are listed in Table 4. Meyer C. [75] had the maximum citations of 691 on their article titled "The greening of the concrete industry". However, Shayan A. [76] and Topcu I.B [39] had 363 and 342 citations on their respective articles and have been ranked in the top three. Figure 8 shows the author's visualization having the most article citations on their respective publications (Figure 8a), the top connected articles (Figure 8b), and density visualization of connected articles (Figure 8c) in the present study field. It was observed that the connected documents were 88 out of 102 based on citations. The network of co-citations between the writers participating in the study of WG utilization in concrete for sustainable construction is depicted in this visualization. The closeness of the articles depicts how interconnected they are with each other in terms of citations.


**Table 4.** Top 20 publications based on citation count.


**Table 4.** *Cont.*

(**a**)

**Figure 8.** *Cont.*

(**c**)

**Figure 8.** Mapping of documents; (**a**) documents with minimum 100 citations; (**b**) connected documents based on citations; (**c**) density of connected documents.

#### *4.6. Countries Mapping*

Certain nations have contributed more than others in the current research domain in the past and continue to do so. The visualization network was developed to help readers visualize regions that are deeply committed to sustainable construction. The "type of analysis" was "bibliographic coupling", and the "unit of analysis" was "countries". The criterion for a country's minimum number of documents was set at 5, and 37 of 87 countries met the criterion. The top 20 active nations are listed in Table 5 based on the number of documents and citations related to the present study area. India, United States, and China contributed the most documents overall, with 126, 63, and 52 documents, respectively. While the United States, Australia, and United Kingdom were the top three participating countries in terms of citation count, with 2778, 2098, and 1857 citations, respectively. The number of documents, citations, and total link strength indicates a nation's influence on the evolution of the current research domain. The total link strength indicates the extent to which a country's documents have influenced the other countries participating in these studies. The United States had the strongest total link strength in comparison to other countries, followed by Australia and China. As a result, the aforementioned countries

were determined to have the greatest influence on the utilization of WG in concrete for sustainable construction. Figure 9a,b illustrates the countries' connectivity and density visualization of countries that are connected through citations. The frame's size indicates the country's contribution to the field of study. Additionally, the density visualization demonstrates that the countries with the highest participation had a higher density. Future researchers will be aided in establishing scientific collaborations, producing joint venture reports, and sharing innovative techniques and ideas by the graphical representation of participating countries.


**Table 5.** Top 20 contributing countries.

(**a**)

**Figure 9.** *Cont.*

(**b**)

**Figure 9.** Countries mapping: (**a**) network visualization: (**b**) density visualization.

#### **5. Types and Properties of Waste Glass**

WG is classified chemically as lead, soda-lime, electric, and borosilicate glass. The most widely utilized type of glass is soda-lime glass. The main chemical composition of glass includes SiO2, Na2CO3, and CaCO3 [77]. Table 6 lists the percentage of various chemical compounds in different kinds of glass. Glass is classified according to its color into three categories: clear/flint, green, and brown/amber glass [78]. Glasses come in a variety of colors due to their chemical compositions, which relate to distinct levels of color impurity. Color impurity is limited to 4–6%, 5–30%, and 5–15% in clear, green, amber glass, respectively [77]. Glass is classified according to its application into six categories, namely, plate glass, container glass, continuous filament glass, mineral wool insulation, specialty glass, and domestic glass or tableware [77]. Between these types, plate and container glass are typically made of soda-lime glass; domestic glass is typically made of lead or soda-lime glass; continuous filament glass is typically made of electric glass; borosilicate glass is used to insulate mineral wool, and specialty glass is frequently made of borosilicate or soda-lime glass.


**Table 6.** Chemical composition of various kinds of waste glass [77].

#### **6. Waste Glass Utilization in Cement-Based Materials**

WG can be utilized in CBMs as aggregate replacement and cement replacement. Thus, it conserves natural resources, solves waste management problems, reduces CO2 emission by decreasing cement demand, protects the environment from toxic chemicals, and produces cost-effective composites. Therefore, the utilization of WG in construction materials is a better approach for sustainability in construction. In this section, the effect of utilizing WG

on fresh and hardened properties of CBMs, including workability, compressive strength (CS), split-tensile strength (STS), and flexural strength (FS), are reviewed. Furthermore, the microstructure and durability of composites containing WG are investigated. Different limitations associated with WG use in CBMs and their possible solution are reported.
