Steel Fiber-Reinforced Concrete: A Systematic Review of the Research Progress and Knowledge Mapping

This study performed a scientometric-based examination of the literature on steel fiber-reinforced concrete (SFRC) to identify its key elements. Typical review papers are limited in their capacity to link distinct segments of the literature in an organized and systematic method. The most challenging aspects of current research are knowledge mapping, co-occurrence, and co-citation. The Scopus search engine was used to search for and obtain the data required to meet the goals of the study. During the data evaluation, the relevant publication sources, keyword assessment, productive authors based on publications and citations, top papers based on citations received, and areas vigorously involved in SFRC studies were recognized. The VOSviewer software tool was used to evaluate the literature data from 9562 relevant papers, which included citation, abstract, bibliographic, keywords, funding, and other information. Furthermore, the applications and constraints related to the usage of SFRC in the construction sector were examined, as well as potential solutions to these constraints. It was determined that only 17 publication sources (journals/conferences) had published at least 100 articles on SFRC up to June 2022. Additionally, the mostly employed keywords by authors in SFRC research include steel fibers, fiber-reinforced concrete, concrete, steel fiber-reinforced concrete, and reinforced concrete. The assessment of authors revealed that 39 authors had published at least 30 articles. Moreover, China, the United States, and India were found to be the most active and participating countries based on publications on SFRC research. This study can assist academics in building collaborative initiatives and communicating new ideas and techniques because of the quantitative and graphical depiction of participating nations and researchers.


Introduction
Concrete is a composite, brittle material utilized in a variety of engineering structures, including foundations, pavements, tunnels, bridges, walls, reservoirs, and dams [1][2][3]. Because of these numerous uses, a great deal of research has been conducted to enhance the characteristics of concrete for greater applicability [4][5][6][7][8][9][10]. The addition of steel to concrete was one of many attempts to improve its performance [11][12][13][14]. These traditional reinforcements are steel reinforcing bars positioned at precise locations inside the structure to resist applied tensile and shear stresses [15,16]. In contrast, the integration of steel fibers is often discontinuous and random in the concrete mixture [17][18][19]. For concrete mixtures in which the fibers are evenly scattered, they serve a significant role in reducing the incidence of cracks caused by variations in relative humidity and temperature [20][21][22][23]. The addition of fibers (steel/natural/synthetic) to the cementitious mixtures improves their mechanical properties [24][25][26][27][28]. Although the role of fiber might not always involve an increase in strength, it has a considerable favorable effect on ductility, resilience to dynamic loading, and toughness [29][30][31][32][33][34][35]. Concrete reinforcement with fibers is not a substitute for traditional

Review Strategy
This work used scientometric evaluation of bibliometric data [60][61][62] to quantify the many aspects of the literature. Scientific mapping, a method built by specialists for bibliographic records processing, is used in scientometric investigations [63,64]. Many papers have been recorded on the topic under study; hence, it is critical to use a reliable database. Web of Science and Scopus are two highly reliable databases that are ideal for this reason [65,66]. Scopus, which is strongly advised by scholars [67,68], was utilized to gather bibliographic data on SFRC research. A Scopus search for the keyword "steel fiber reinforced concrete" returned 18,481 items as of June 2022. To minimize extraneous papers, many filter settings were used. Table 1 indicates the complete method of data extraction, evaluation, and the different limits/filters used during the study. Furthermore, numerous investigations have documented a similar approach in different fields of study [69][70][71][72]. After applying these restrictions to the Scopus database, 14,110 items remained. Scopus records were stored in Comma Separated Values (CSV) format for further screening. It was found that the files retrieved also contained the data on fiber-reinforced polymers, which were removed manually, and only SFRC data comprising 9562 items were used for further analysis using the software tool. The scientific representation and quantitative assessment of the received information were built using VOSviewer (version 1.6.18). VOSviewer is a publicly accessible, open-source mapping product that is regularly used in numerous research disciplines and proposed by academics [73,74]. Therefore, the present study's aims were fulfilled by using VOSviewer. The resultant data (CSV files) were imported into VOSviewer, and analysis was carried out while data consistency and reliability were maintained. The publishing sources, the most often occurring keywords, the researchers with the most published papers and citations, the documents with the most citations, and the state's engagement were all analyzed during the scientometric study. Graphs were presented to depict the distinct attributes, their interrelationships, and co-occurrence, while tables were constructed to display quantitative data.

Research Progress
The Scopus analyzer was used to find the most pertinent research fields for this assessment. Engineering and Materials Science were judged to be the top two documentgenerating fields, with about 52% and 31% of papers, respectively, providing a total of 83% of documents in the SFRC study, as shown in Figure 1. Furthermore, the Scopus database was searched for types of publications on the topic study field (Figure 2). Based on this analysis, journal papers, conference articles, conference reviews, and journal reviews comprised around 69%, 28%, 2%, and 1% of all data, respectively. As the first paper on the SFRC research was found in 1972, Figure 3

Mapping Publication Sources
A VOSviewer software was used to evaluate publication outlets (journals/conferences) based on bibliographic data. A minimum of 100 articles limit for a source was set, and 17 of the 1115 sources met this condition. Table 2 displays the sources that contain at least 100 papers on SFRC research up to June 2022, as well as the number of citations received during that time. The top three publishing sources, based on total publications, were discovered to be "Construction and building materials (CBM)", "Engineering structures", and "American concrete institute, ACI special publication", with 877, 420, and 403 documents, respectively. Furthermore, the top three sources-based citations received up to June 2022 are "CBM", which received 29,863, "Cement and concrete research", which received 9749, and "Cement and concrete composites", which received 9708 citations. This analysis, in particular, would lay the framework for future scientometric evaluations in SFRC research. Furthermore, earlier typical review studies were unable to provide a systematic overview of the literature. Figure 4 shows an image of sources that have published at least 100 articles. Based on document count, the frame dimension in Figure 4a is related to the outlet's influence on the research field under study; a larger frame size suggests a stronger impact. As an example, "CBM" has a wider frame than the others, indicating that it is a journal of significant value in the current study field. Four groups/clusters were constructed, each with its own color on the map (blue, yellow, red, and green). The extent of the research outlet or the frequency with which they are co-cited in related papers is used to form groups/clusters [75]. The VOSviewer classified sources based on their co-citation rates in publications. The red cluster, for example, comprises nine items that have been co-cited many times in the same papers. Additionally, the connections between close frames (publishing sources) in a group/cluster are stronger than those between widely dispersed frames. As an example, "CBM" has a stronger correlation with "Cement and concrete composites" than with "ACI materials journal". As shown in Figure 4b, different colors correlate to different density concentrations for a journal/conference. Red has the largest concentration of density, followed by yellow, green, and blue. "CBM" and "Engineering structures" are highlighted in red, indicating

Mapping Keywords
Keywords are important in research since they differentiate and highlight the primary subject of the research area [76]. The lowest repeating threshold for a keyword was maintained at 50, and 81 of the 12,955 keywords were retained. Table 3 displays the leading 30 keywords that appear most regularly in the literature. Steel fibers, fiber-reinforced concrete, concrete, steel fiber-reinforced concrete, and reinforced concrete are the five highly regularly occurring keywords in the SFRC research. Based on the keyword assessment, the insertion of steel fibers in concrete has mostly been studied to enhance the mechanical and durability performance of concrete, particularly to control brittleness, resist crack propagation through crack bridging, and increase ductility. Figure 5 depicts a systematic graph of keywords with co-occurrences, linkages, and density proportionate to their rate of occurrence. The dimensions of a keyword's frame in Figure 5a show its frequency, while its location shows its co-occurrence in articles. Furthermore, the map shows that the leading keywords have bigger frames than the others, implying that these are critical keywords for critical analysis in SFRC studies. The map emphasizes groups/clusters in a way that demonstrates their co-occurrence in a range of published articles. The co-occurrence of multiple terms in articles determines the color-coded grouping. Figure  5a depicts five clusters in various hues. Different colors reflect different keyword density concentrations, as seen in Figure 5b. The colors red, yellow, green, and blue are sorted in order of density strength, with red having the highest density concentration and blue having the lowest. Steel fibers, fiber-reinforced concrete, concrete, and other notable keywords are highlighted in red or yellow, suggesting a higher density of occurrences. This

Mapping Keywords
Keywords are important in research since they differentiate and highlight the primary subject of the research area [76]. The lowest repeating threshold for a keyword was maintained at 50, and 81 of the 12,955 keywords were retained. Table 3 displays the leading 30 keywords that appear most regularly in the literature. Steel fibers, fiber-reinforced concrete, concrete, steel fiber-reinforced concrete, and reinforced concrete are the five highly regularly occurring keywords in the SFRC research. Based on the keyword assessment, the insertion of steel fibers in concrete has mostly been studied to enhance the mechanical and durability performance of concrete, particularly to control brittleness, resist crack propagation through crack bridging, and increase ductility. Figure 5 depicts a systematic graph of keywords with co-occurrences, linkages, and density proportionate to their rate of occurrence. The dimensions of a keyword's frame in Figure 5a show its frequency, while its location shows its co-occurrence in articles. Furthermore, the map shows that the leading keywords have bigger frames than the others, implying that these are critical keywords for critical analysis in SFRC studies. The map emphasizes groups/clusters in a way that demonstrates their co-occurrence in a range of published articles. The co-occurrence of multiple terms in articles determines the color-coded grouping. Figure 5a depicts five clusters in various hues. Different colors reflect different keyword density concentrations, as seen in Figure 5b. The colors red, yellow, green, and blue are sorted in order of density strength, with red having the highest density concentration and blue having the lowest. Steel fibers, fiber-reinforced concrete, concrete, and other notable keywords are highlighted in red or yellow, suggesting a higher density of occurrences. This finding will support ambitious scholars in selecting keywords that will aid in recognition of available papers on a particular topic. Fiber-reinforced concrete 108 25 steel fiber-reinforced concrete (SFRC) 108 26 High strength concrete 106 27 Tensile strength 105 28 Flexural behavior 94 29 Fiber-reinforced concretes 93 30 Composite materials 92

Mapping Authors
Citations demonstrate a scientist's significance in a certain field of research [77]. The minimum paper criteria for a researcher was set at 30, and 39 of 14,611 researchers met this condition. Table 4 shows the authors with the most papers and citation count in the field of SFRC, as revealed using bibliographic data and VOSviewer. The average citations for a writer were computed by dividing the total number of citations by the total number of papers. It is complicated to evaluate a researcher's performance when all indicators, like the number of documents, average citations, and total citations, are considered. Alternatively, the researcher's rating will be assessed separately for each component. According to the data analysis, Zhang Y. is the most productive researcher, with 86 publications, followed by

Mapping Documents
The number of citations received by an article indicates its significance in a certain academic topic. Papers with a high number of citations are considered to be pioneering in their respective academic fields. The minimum number of citations for a document was set at 150, and 123 of 9562 publications satisfied this requirement. Table 5 includes the top five documents in the area of SFRC based on citations, as well as their authors and citation counts. Song P.S.'s [78] paper "Mechanical properties of high-strength steel fiber-reinforced concrete" has received 593 citations. Brandt A.M. [79] and Park S.H. [80] acquired 552 and 406 citations, respectively, for their works, placing them in the top three. However, only 60 publications had received more than 200 citations as of June 2022. Furthermore, Figure 7 illustrates the scientific visualization of papers and their connections to the subject of the current study based on citations. Figure 7a

Mapping Documents
The number of citations received by an article indicates its significance in a certain academic topic. Papers with a high number of citations are considered to be pioneering in their respective academic fields. The minimum number of citations for a document was

Mapping Countries
Various states have participated with more materials in the present research topic than others, and they intend to continue doing so. The systematic graph was built so that readers may look at areas dedicated to SFRC research. The minimum number of papers that a country may possess was set at 50, and 35 countries met this requirement. Table 6 shows that the nations represented have published at least 50 documents on the current study topic. China, the United States, and India published the most papers, with 1607, 1139, and 923 papers, respectively. Furthermore, the United States obtained 24,770 citations, China received 22,924 citations, and Italy received 12,190 citations. The systematic map and the density strength of nations linked by citations are depicted in Figure 8. The size of a frame in Figure 8a is proportionate to a country's effect on the topic studied based on the number of documents published. Figure 8b displays that the nations with the highest degree of involvement had a higher density. The graphical interpretation and quantitative record of the participating countries will help young scientists form scientific alliances, create joint companies, and exchange new approaches and thoughts. Scholars from nations interested in conducting SFRC studies can cooperate with specialists in the field and benefit from their experience.  Iran  320  6586  10  Japan  312  4089  11  Spain  293  5216  12  Iraq  266  1533  13  Germany  260  2900  14  Turkey  255  6507  15  Malaysia  180  2328  16  Egypt  171  1151  17  Portugal  166  3902  18  Poland  156  2223  19 Saudi

Discussions and Applications of SFRC
This systematic study performed statistical analysis and mapping of the SFRC re search using bibliographic data. Previous manual review studies lacked the ability to link distinct regions of the literature entirely and accurately. This study found the publication' sources (journals/conferences) that published the most documents, the most often used keywords in publications, the documents and researchers with the greatest citations, and

Discussions and Applications of SFRC
This systematic study performed statistical analysis and mapping of the SFRC research using bibliographic data. Previous manual review studies lacked the ability to link distinct regions of the literature entirely and accurately. This study found the publication's sources (journals/conferences) that published the most documents, the most often used keywords in publications, the documents and researchers with the greatest citations, and the nations that were actively engaged in SFRC research. According to keyword analysis, the incorporation of steel fibers in concrete has mostly been explored to improve the mechanical and durability performance of concrete, especially to reduce brittleness, resist fracture propagation by crack bridging, and increase ductility. Furthermore, the literature and its citations were analyzed to identify highly devoted and participating nations based on publication count. The graphical depiction and quantitative analysis of participating nations and researchers will aid young scientists in making scientific collaborations, instituting joint ventures, and exchanging new methodologies and concepts. Scholars from nations intent on extending research on the use of SFRC can cooperate with experts in the field and benefit from their knowledge.
SFRC has been utilized in a variety of applications, including bridges, tunnel linings, retaining walls, road pavements, slabs, hydraulic structures, shotcrete, foundations, and precast members [83][84][85][86][87][88][89][90][91][92]. SFRC is helpful in roadway pavement and precast members because of its high flexural strength, reduced total pavement thickness, and increased resilience to impact and repetitive loads [93][94][95][96]. When utilized in hydraulic constructions, SFRC has a strong resistance to eroding induced by the rapid passage of water [97][98][99]. Fiber shotcretes are particularly effective for rock slope stability, tunnel lining, and bridge rehabilitation [100][101][102][103]. However, the introduction of 1% industrial steel fiber doubles the material expense [104]. Thus, the usage of steel fiber derived from used tires has become a viable alternative for the production of SFRC. The performance of concrete reinforced with recycled steel fibers is equivalent to that of industrial SFRC [105][106][107]. This provides an ecologically friendly solution to some of the issues linked with the production of discarded tires [108]. In addition, it assists to promote sustainability in the building sector [109][110][111]. Another challenge to the use of SFRC is corrosion of steel fibers, but coating (brass/zinc/copper) the steel fiber can help resolve this issue [112][113][114]. Furthermore, getting the uniform dispersal of steel fibers in the matrix is another issue related to the use of SFRC. However, using the layer procedure for missing the ingredients of SFRC is the best suitable option to achieve the uniform dispersion of fibers [4,115].

Conclusions
The goal of this study was to carry out a scientometric-based review of the current literature on SFRC research in order to evaluate several criteria. Scopus was searched for 9562 relevant articles, and the records were assessed using the VOSviewer tool. This research yielded the following findings: • An assessment of publishing sources (journals/conferences), including articles on SFRC research, revealed that "CBM", Engineering structures", and "American concrete institute, ACI special publication" are the top three sources, with 877, 420, and 403 publications, respectively. In terms of total citations, the top three publishing sources are "CBM" with 29,863, "Cement and concrete research" with 29,863, and "Cement and concrete composites" with 9708 citations. • Keywords analysis on the SFRC research revealed that steel fibers, fiber-reinforced concrete, concrete, steel fiber-reinforced concrete, and reinforced concrete are the five most often occurring terms. The keyword analysis found that steel fibers incorporation in concrete has mostly been investigated to improve the mechanical and durability performance of concrete, especially to control the brittleness resisting the crack propagation through cracks bridging and improve ductility. The major challenges to the use of SFRC include high cost, corrosion of steel fibers, and uniform dispersion of fibers in the mix. However, when using recycled steel fibers, especially from the waste tires, coating steel fiber with zinc/brass/copper can be better solutions to these challenges.

Data Availability Statement:
The data used in this research has been properly cited and reported in the main text.