3.2. Quantitative and visual analysis of the number of national publications
The government, educational and scientific research institutions serve as source of scientific research funds to support research projects. The state completes the management and overall control of the institutions by promulgating decision-making and setting relevant regulations. Therefore, the total number of published articles in a country or region can also, intuitively, reflect the focus and development trend of research in this field. The national coauthorship and relationship map, not only shows the postings of each country, but also visually shows the cooperation and connection between countries. In general, the national coauthored visualization map shows a large number of countries have cooperated in the research of reused brick. Among them, countries with closer cooperation and coauthorship can be regarded as existing, with some consensus reached among academic viewpoints, for example, with the recycling methods or relevant application cases of reused bricks). This provides the possibility for scholars to verify the reproducibility of their workflow after proposing methods for material recycling.
The country node type was set to country, the time slice was set to 1 year, and the country and regional time zone graph of this field was generated in order of the first release time. The collaborative network had 106 nodes and 309 connections, and the network density was 0.0555. In terms of the number of articles, the top five countries in terms of number of papers are China (84 articles, the earliest recorded in 2007), India (53 articles, the earliest in 2007), Italy (45 articles, the earliest recorded in 2007), Bibliography 2007), Spain (40 articles, earliest bibliography 2008), and Brazil (38 articles, earliest bibliography 2010). The connection between nodes expresses the cooperation and connection between countries. In the past 20 years, an increasing number of countries have begun to carry out research and cooperation in this field. It is worth mentioning that although China ranks first in the number of
published papers, reaching 84, it has cooperated less with other countries. Approximately 80% of the papers are close to domestic cooperation and coauthored by scholars from the same institution. There is no cooperation with other countries (India, Italy, Spain, Brazil) that contribute greatly to the publication volume. In contrast, there is close cooperation between Western countries, such as Finland, the United Kingdom, Italy, Switzerland and other countries, which means, in the future, Western scholars will establish closer ties and carry out further academic cooperation.
3.4. Topic category classification and co-occurrence analysis of research areas
The node type was set to category and the time slice to 1 year to generate a co-occurrence graph of the topic categories. A total of 240 nodes were obtained, a total of 1158 connections were made, and the network density was 0.0404. More precisely, related research was carried out on a total of 240 disciplines of reused brick, and 1158 interdisciplinary research and cooperation studies were produced. According to the citation frequency, Engineering and Environmental Science are the contributions of the &Ecology study in 1994, which produced 345 and 177 papers, respectively. This was followed by Materials Science (2001, 173 papers) and Construction & Building Technology (2002, 144 papers). The visual map of the subject area visually displays the above information, and the larger the node radius in the map is, the greater the number of contributed articles and build connections between disciplines. It is worth mentioning that there are only 24 literature records in the field of architecture, and there are few and weak connections between the discipline of architecture and related disciplines such as construction & building technology, engineering, and green & sustainable science & technology. Contact and expand academic influence.
3.5 Keyword visualization map
Keywords are a high-level summary of the research content in the form of representative words and are regarded as one of the most important components of a research article. The main scientific research area can usually be identified by keywords, and the high frequency and centrality of keyword co-occurrence can reflect the main theme of the research (Barbu et al. 2022;Gao et al. 2021). The visual analysis of similar keywords is helpful to intuitively help scholars understand the research hotspots and main issues in the field and to better distinguish research clusters and the degree of correlation between the clusters.
The research quantitatively analyses the words or phrases that frequently summarize the research content, conducts a cluster analysis and draws a visual network according to the preinertial strong and weak relationship between keywords. (Meng et al. 2020;Callon, Jean-Pierre, and Francoise 1991).
In this analysis, the research hotspots in the past five years are highlighted, the current situation in this field is revealed, and the cluster correlation is studied. In the visual map generated by VOSviewer, it is found that the core keywords of the overall research content are construction, recycling, construction and demolish waste (CDW), building, system and technology, and energy sustainability. The clusters are closely related and cross-research thematic content.
Table 2
|
Cluster A(Blue)
|
Cluster B(Green)
|
Cluster C(Red)
|
|
Construction
|
Building
|
Compressive strength
|
|
Concrete
|
System
|
Sample
|
|
Recycled aggregate
|
Technology
|
Absorption
|
|
Demolition
|
Energy
|
Temperature
|
|
Demolition waste
|
Sustainability
|
Clay
|
With the passage of time, observing the hot spots in the research field (after 2017) the keyword demolition waste field has gradually become a real word with a relatively short distance from construction and building in the map. Therefore, bricks used in CDW have become an important source of material for research in this field.
3.6. Research subject area clustering
Based on the cluster analysis of keywords based on the CiteSpace platform, the figure shows the topic clustering of the reused brick research field (from 1977–2022), and has a total of 18 automatically generated timeline labels and 11 key clusters. These clusters, the hot topics, influence, relevance, and main content under topic clustering are displayed. Combined with the development context and correlation characteristics of reused bricks, as shown in the figure, the analysis results are as follows:
#1 Clustering—The research topic of clustering is mechanical properties. There are 51 documents in this cluster, and the earliest document was published in 2013. Since 2016, the number of published papers has gradually increased, from 5 to 13 per year. The cluster, includes clay brick powder;
structural lightweight aggregate concrete; crushed clay brick aggregate; sanitary ceramic waste | compressive strength; cement mortar; cement lime; brick masonry waste; limestone dust as the main research fields. The main research keywords are waste, brick, concrete, clay, compressive mechanical, property, aggregate, and powder. In the core literature, Halicka, Anna et al. proposed a way to pulverize the sanitary ceramic waste resources in domestic waste and reuse it as a new aggregate in concrete. The aggregate production process and verification method of this high-temperature and wear-resistant concrete are also detailed in the study, and this concrete can be used for the components working under high-temperature conditions (Halicka, Ogrodnik, and Zegardlo 2013).
With the rapid development of the world economy, the treatment and placement of sewage sludge has become an urgent issue around the world. In addition to landfill and agricultural applications, fertilization and other recycling methods are more important in recycling back within the building and construction industry. Taking the sewage sludge recovered from the municipal sewage treatment plant in the suburbs of Patras, Greece, as an example, Zbyšek Pavlík et al. proposed a design and heat treatment method of sewage sludge for mixed cement, aiming to apply it to mixed cement to reduce energy demand. A life cycle assessment was carried out, which showed that using part of sewage sludge as a substitute for part of cement has huge environmental and economic benefits (Pavlík et al. 2016). Chang Zhiyang et al. reviewed the published literature and found that sewage sludge can be thermally treated to replace raw materials in construction and building material production, providing a solution for the recycling and reuse of sludge treatment resources. Sewage sludge can be used as a raw material for the production of ecological cement and bricks in building materials. It is used as an alternative material in cement, a supplementary additive in gel materials and in bricks, ceramic materials, light aggregates, etc. Sewage sludge should be no more 20% of the total ratio when used as a replacement material, to ensure a building material with good mechanical structure Chang et al. 2020).
#2 Clustering—The research topic of the clustering is building materials. There are 14 documents in this clustering, and the earliest document was published in 2004. The cluster includes ceramic composites; energy saving; refractory; ceramic bricks | clay bricks; secondary raw material; pyrrhotite ash; and technological properties. The main keywords of the study were waste; activation; regeneration; blue; removal materials; ceramic; building; energy; extrusion. The thermodynamic calculation analysis of scholars, such as Wanchao Liu, has proven that the recovery of iron is combined with the reuse of aluminium silicate slag, and aluminium silicate slag is used to prepare building materials. It can realize zero discharge of the Bayer process red mud (Liu, Yang, and Xiao 2009). Anja Terzić et al. observed the macroscopic properties and microstructure of fly ash minerals through chemical experiments, proving the use of fly ash recovery and reuse in the building and building materials industry. It can also be used as an ingredient in cement, mortar, concrete, bricks and ceramics and glass/glass ceramics (Terzić, Pavlović, and Miličić 2013). Diego Alexis Ramos Huarachi et al. summarize the literature on the LCA of bricks and consider alternative and traditional bricks from the development and design stages to complete the process. In terms of environmental assessment, alternative bricks are manufactured with organic (ABO) or inorganic (ABI) additives, often waste from multiple industries. The main difference in the production process is the omission of firing. Further research is recommended to increase the knowledge base of traditional bricks (TB), such as clay bricks, ceramic bricks and concrete bricks, floor tiles (wood embryos), and waste bricks.
With regard to finding new materials (waste) for the production of replacement bricks, the benefits of recycling are quantifiable (Ramos Huarachi et al. 2020). Tibor Kovács et al. demonstrated that under high-temperature processing conditions, from a radiological point of view, manganese clay and red mud can be used as materials for manufacturing and additives, ensuring the use of manganese clay to produce safe building materials (Kovács et al. 2017). Unlike mechanical properties, chemical and molecular dynamics studies have been carried out experimentally. Anne Sigrid Nordby et al. proposed brick as a building material whose extremely high durability can be seen as beneficial to the environment during its life cycle. The bricks themselves act as reusable components, increasing the potential for a secondary service life. Degradation cycles can be avoided by investigating how component design and construction methods affect reusability. The ideal brick connection method, better cleaned lime-based mortar, bolt connection and other methods were proposed to achieve nondegradable reuse of bricks and reset the life cycle of bricks to increase their availability (Nordby et al. 2009).
#3 Clustering — The topic of clustering research is compressive strength. There are 44 documents in this cluster, and the earliest document was published in 2001. The volume of research on this topic is generally on the rise. The cluster includes paper mill waste, light weight, shock absorbing, waste-create bricks | clay bricks, historical materials, brick production, textile sludge, and waste glass as the main research areas. The main research keywords are waste; compressive; strength; bricks; recycle brick; clay; treatment; sugarcane; rice. Andrea Mezencevova et al. attempted to make a deposition transfer and passed the evaluation based on mechanical properties and ASTM building transfer standards. In this experiment, by controlling the ratio of the raw materials for making bricks and the amount of sediment dredged in the Savannah Harbour, the sedimentary bricks were prepared with a raw material mixture composed of the hard mud extrusion process, and the production of the fired bricks was completed, which is regarded as a meaningful and productive alternative away of making bricks (Mezencevova et al. 2012) . S.P. Raut et al. completed the production of low carbon footprint bricks prepared with RPMW-cement by recycling paper mill waste (RPMW) used to make building bricks and mixing it with different contents of cement. Bricks made from RPMW-cement are a lighter and more economical new transfer material. Finally, by comparing the physical and mechanical properties of different prepared brick samples, it is found that the compressive strength of the brick reaches 9 MPa, which is three times that of traditional clay bricks (3 MPa) and meets the requirements of BS6073 for building materials for indoor structural applications and requirements. RPMW−10% cement is the best composition (Raut et al. 2012) . F. Messina et al. combined calcined, water soluble sludge (CWPS) with calcined clay sediment (CCS) as a sustainable geopolymer binder for geopolymer materials. The product was upgraded to a typical, precast concrete element.
Something even more cost-effective is the recycling of residues from reservoir dams to produce building components, which also alleviates the demand for building materials due to population growth (Messina et al. 2017). C. Huang et al. also used reservoir dam residues and water treatment plant sludge as raw materials and used a sintering process to make transfers. Their compressive strength and capacity met the national first-class transfer standard and met the requirements of tiles (Huang et al. 2001). Dina M. Sadek et al. prepared concrete bricks by recycling waste tire rubber as aggregates and evaluated the structural behaviour and main characteristics of rubber masonry walls under compressive loads through comparative experiments. This opened up a new field of load-bearing and nonload-bearing cement bricks made from concrete and waste tires (Sadek and El-Attar 2015).
# 4 clusters and 6 clusters --- the clustering research topic is demolish waste. Clustering about demolish waste, construction and demolish waste produced a total of 21 documents, and the earliest document was published in 2012. The overall research is on the rise, with less attention in this field from 2013 to 2017 and more research results after 2018. The two clusters included fatigue strength; pet plastic; cement stabilization; shear strength | demolition materials; resilient modulus; shear strength; clay ceramic waste; construction waste, separation techniques; quality improvement; concrete rubble; chemical composition | plastic waste; brick rubble; pestle analysis; leaching test; artificial neural network and other topics. The main keywords of the research were sustainability; material; bricks; recycled; concrete; clay; aggregates; building; compressive residential; carbon; property; emission; recycling; recycling potential of demolition waste. Taking Shenzhen as an example, a large amount of CDW waste is generated in urban renewal. Inert demolition waste places great pressure on urban renewal, including 18.41 million tons of recyclable bricks, 7.02 million tons of mortar, 28.36 million tons of aggregate, and 4.16 million tons of lightweight wallboard. Therefore, a redrawing process of demolition waste recycling is proposed. Quantitative models and quantitative indicators of different types of waste are established so that future work can comprehensively calculate the environmental benefits and economic values of different types of waste (Yu et al. 2020). Marzieh Kianimehr et al. attempted to recycle construction and demolition materials as recycled concrete aggregates (RCAs) mixed with clay for use in pavement structures and nonstructural elements (Kianimehr et al. 2019) . Carlos HoffmannSampaio et al. separated concrete, brick and gypsum particles from CDW recycled aggregate. It was found that in the crushed sample material, an efficient sorting process of low-quality CDW recycled aggregate allowed the reuse of the separated concrete, brick, and gypsum particles (Sampaio et al. 2016). The work of Lihua Zhu et al. recovered clay brick waste in CDW and ground it into tiny particles, which acts as binders in mortar and concrete and replaces natural coarse aggregates. This reduces the consumption of natural resources and completes the reuse of construction waste cycle (Zhu and Zhu 2020). The work of Chi-SunPoon and DixonChan is focused on Hong Kong, where land resources are scarce and districts are densely populated. Different specifications of recycled aggregate produced by the Hong Kong government are discussed. Broken bricks and tiles are used as substitutes for fine aggregates, and the double-mix method is used to improve the compressive strength of concrete, so broken bricks and broken ceramics are also regarded as new recycled concrete aggregates (RCAs) (Poon and Chan 2007).
# 5 Clustering—The theme of clustering research is heavy metals. There were a total of 21 documents. The earliest document was published in 2004, and the total number of studies increased significantly in 2018. Clustering on low cost filtration; irrieation feasibility; hinicipal wastewater; red amaranth | iron oxide; acoustic cavitation; rhizobium population; groundwater contaminants; fly ash brick clay and other topics occurred. The main keywords of the research were deacidification; histosols; technosols; land; drilling population; pulses; nutrients; productivity; rhizobium. Zhiyang Chang et al. conducted a literature review on the possibility of sludge treatment and resource recovery during construction and building material production. After incineration, sludge ash can be used as a raw material to produce ecological cement, brick, ceramic materials and aggregates through a sintering process, as well as supplementary admixtures for cement materials. In addition, the extraction of metal elements from sewage sludge into valuable products can be completed before sewage sludge is used as supplementary cementing materials (SCMs) while preventing secondary environmental pollution (Chang et al. 2020).
Research by Ivana Jelić et al. is based on the "3R" principle (reduce, reuse and recycle) and evaluates construction and demolition waste (C&DW) concrete, façade, asphalt, and different types of sample brick sampling analysis. The material characterization was analysed by techniques such as XRD and FT-IR, and adsorption experiments were performed to summarize the composition and differences of ions in the samples. Ultimately, CDW proved to be noncorrosive and not radiologically hazardous to human health and the environment (Jelić et al. 2018). Zhikun Zhang et al. tried to use oil shale fly ash (OSFA) in CDW as a byproduct of shale oil extraction in the oil shale industry, and through melting and sintering, it was recovered into value-added OSFA-based glass ceramic material. Furthermore, due to its excellent chemical resistance, it can be used as an alternative material for construction applications (Zhang, Zhang, and Li 2015). Gunvor M. Kirkelund et al. recycled fly ash produced by the centralized incineration of waste and performed electrodialysis to remove heavy metals to realize the reuse of fly ash. It is expected that treated fly ash can replace cement in concrete or clay in bricks and be seen as a new potential building material (Kirkelund and Jensen 2018). It is important to explore how to reduce metal mobility in materials, such as waste, sewage sludge, textile wastewater sludge, sediments, etc., so that the material is not harmful to the environment (Zhan et al. 2020;Couvidat et al. 2016༛Cappuyns and Swennen 2009)
#7 Clustering—The subject of clustering research is marine sediment. There were 4 studies, and there were research records from 2016 to 2019. Clustering was about leaching test; weathering cells; cemented mortars; environmental evaluation | clay bricks; mechanical properties; thermal conductivity; leaching test; thermal solidification and other topics. The main research keywords were materials; manufacture; technology; microstructure; thickness aggregate; lightweight; artificial; sewage; microstructure. Almost all studies use marine sediments as a substitute for fine aggregates, such as sand, and through a series of experiments on chemical and material mechanical properties, it is proven that this method can be used as cement mortar for nonstructural applications or for building materials such as clay bricks and tiles. Made (Couvidat et al. 2016;Couvidat et al. 2016;Baksa et al. 2018;Baksa et al. 2018;Zelleg et al. 2018).
#8 Clustering --- The clustering research theme is life cycle assessment. There were 11 papers in total, and the first document was published in 2004. The overall research is on the rise, with less attention in this field from 2005 to 2015 and more research results after 2016. Mara ReginaMendes et al. compared the environmental impacts of municipal solid waste incineration and landfills in Sao Paulo, Brazil, using a life cycle assessment (LCA) method. Based on the current situation where electricity is mainly hydroelectric in Brazil, the assessment found that landfilling has a greater impact on the environment than incineration and that the switch from landfilling to incineration of waste disposal will reduce the overall environmental impact while recovering energy (Mendes, Aramaki, and Hanaki 2004). Yanqing Wang et al. found that in China, the disposal of solid waste in cities is mainly landfill (65.5%) and incineration (32.5%). The emergy method was used to evaluate an integrated waste incineration system in the city. The incineration subsystem and concrete paving bricks with bottom ash (BA) as raw material have the best comprehensive performance in the experiment, which increases the environmental and economic benefits of the waste treatment system (Hong et al. 2017;Wang et al. 2018). Diego Alexis Ramos Huarachi et al. used the life cycle assessment (LCA) method to guide future research. It was found that the drying and burning behaviour of alternative bricks with organic
(ABO) and inorganic (ABI) additives had the greatest potential impact on the environment during the production of conventional bricks (Ramos Huarachi et al. 2020).
# 9 Clustering—The clustering research theme is reuse options, clustering about water treatment; struvite precipitation; adsorption; autoclaved brick | recovery; struvite precipitation; adsorption; autoclaved brick; solidification/stabilization and other topics. The main keywords of the research are carbon; manganese; dioxide; residue; electrolytic flow; personal; care; greywater;, etc., themes. The main research keywords are porphyroblasts, deformation partitioning, spiral axes, and fold mechanisms. # Clustering 11 --- The subject of clustering research is concrete perforated brick. There were 2 papers in this cluster, which were published in 2005 and 2009. Clustering is about recycled aggregales, mixture ratio, shrinkage ratio, masonry structure and other topics. The main research keywords are concrete perforated brick; recycled aggregales; mixture ratio; shrinkage ratio; masonry structure. Since there are no high-frequency words cited in the above three clusters and there is no research relationship network with other studies, it will not be discussed.