Turning Waste into Resources: Bibliometric Study on Sand–Rubber Tire Mixtures in Geotechnical Engineering

Abstract

Improper disposal of waste tires has led to significant environmental and economic challenges, including pollution and inefficient resource utilization. The growing focus on sustainable solutions in geotechnical engineering highlights the potential of sand–rubber tire shred mixtures for applications such as soil stabilization, embankment reinforcement, seismic isolation, and drainage. This paper presents a bibliometric study analyzing research trends, methodologies, and applications of these mixtures from 2000 to 2025, based on 366 relevant publications. The findings indicate a substantial increase in publications after 2015, reflecting heightened academic and industrial interest in sustainable construction materials. Keyword co-occurrence analysis reveals key research themes, including optimization of shear strength, enhancement of compressibility, and mitigation of seismic impacts. Citation network maps illustrate influential studies and collaborative research networks that are propelling advancements in this field. Despite the advantages of sand–rubber mixtures, challenges such as compaction difficulties, variability in rubber particle size, and long-term durability remain to be addressed. Future research should focus on large-scale field applications, standardization of design methodologies, and the integration of advanced computational modeling for performance optimization. This study contributes to the development of sand–rubber mixtures, positioning them as viable and ecological solutions within the framework of circular economy principles and sustainable construction practices.

1. Introduction

The constantly increasing environmental concern for waste tire disposal problems urged researchers and engineers to seek innovative ways for their recycling [1,2,3]. In this framework, sand–rubber tire shred mixtures are being introduced as one of the promising mixtures in geotechnical engineering applications, with potential benefits in soil stabilization, reinforcement of embankments, seismic isolation, and drainage systems [4]. The integration of waste materials into construction and engineering processes not only addresses disposal issues but also contributes to sustainability in infrastructure development. Among these innovations, sand–rubber tire shred mixtures have emerged as a promising solution within geotechnical engineering [5,6]. These mixtures offer a range of potential benefits, including soil stabilization, reinforcement of embankments, seismic isolation, and improved drainage systems [7,8,9,10,11]. The accumulation of discarded tires presents a significant ecological challenge, contributing to land pollution, fire hazards, and water contamination [7]. By repurposing these tires in geotechnical applications, researchers aim to mitigate environmental impacts while enhancing the performance characteristics of soil, such as shear strength, compressibility, and energy absorption [8,12,13,14,15,16]. This dual approach—addressing waste management while improving soil properties—highlights the importance of ongoing research in this area [8].

Mechanical property characterization of sand–rubber mixtures is presented for use in various applications of infrastructure development [17]. Studies have shown that inclusions of rubber change the behavior of the sand, reducing its density while increasing its resilience under loading conditions [18]. Research into the mechanical properties of sand modified with rubber suggests that an optimum rubber content generally falls within a limited range, as this balances the benefits arising from energy dissipation and increased ductility, with potential disadvantages involving loss of stiffness and shear strength [17,19]. The interaction in the mixture due to rubber particles and sand grains controls the overall performance; hence, a determination of adequate mixing ratios must be performed to satisfy various requirements for geotechnical applications [20].

One of the most significant advantages of incorporating rubber tire shreds into sand is the enhancement of dynamic properties, particularly under seismic excitations [21]. The high damping capacity of these mixtures contributes to improved vibrational absorption, positioning them as viable options for seismic isolation systems [21,22]. Furthermore, the sand–rubber mixtures develop smaller unit weight and hence could act as an effective lightweight filling various embankments and retaining walls [4]. All the properties above have encouraged wide-ranging experimental and numerical studies on the feasibility of sand–rubber mixtures in various geotechnical applications [23,24]. Even with such advantages, obstacles regarding compaction problems, material non-homogeneity, and performance issues in the long term must be resolved to identify optimum use [23].

These mixtures have been investigated not only for structural applications but also in the context of environmental hazard mitigation [25]. Their possible application in erosion control, ground stabilization, and blast-induced ground vibration mitigation has recently been investigated [26,27]. Based on various laboratory and field tests, the interaction mechanism between the sand and rubber was understood, and various predictive models developed help in design optimization [28]. Waste tire usage in construction materials falls well within the circular economy’s call for resource efficiency, while reducing reliance on landfills [29].

Despite this, not all research gaps have been able to be covered regarding the long-term behavior of sand–rubber mixtures under different environmental conditions [30]. Some of these issues like durability, degradation due to exposure to weather conditions, and alteration in mechanical properties over time are yet to be investigated [31]. Moreover, design guidelines have to be standardized for the wide applicability of such materials in civil engineering projects. These are only a few limitations, and it calls for collaboration in research between academia and industry for the overcoming of such limitations and identification of best practices regarding waste rubber incorporation into geotechnical engineering applications.

Bibliometric analysis serves as a valuable approach for systematically examining research patterns, key contributors, institutions, and thematic shifts within a specific academic field [32,33,34]. It is a statistical method that offers both quantitative and qualitative insights into scholarly activities [35]. In addition, bibliometric studies evaluate the features of literature, including journal papers, patents, books, and conference papers along with their references which include citations and co-citations [32,33,36]. This tool is further enhanced by co-citation analysis, which looks at citation linkages between papers and allows researchers to find and explore quantitative relationships within their areas of interest [35]. Bibliometrics can be divided into two main categories: one that emphasizes research activity levels and highlights important topics, journals, and countries, and the other that investigates relationships between keywords, institutions, and countries using social network analysis and relationship indicators [32,37,38]. Together, these categories clarify both major and minor themes in a specific area and show how they change over time. Consequently, bibliometric analysis supports scholars in evaluating the existing body of knowledge, recognizing pivotal works, and identifying research trends and gaps that warrant further investigation [39,40,41,42].

This bibliometric analysis provides an overview of the general trend of existing research on sand–rubber tire shred mixtures, applications, and knowledge gaps. The present study is performed to outline the advances in material characterization, mixing methodologies, and field applications by analyzing the volume and distribution of the literature in this domain using a critical analysis of publications from 2000 to 2025. It also seeks to outline future research directions that may contribute to the effective utilization of sand–rubber mixtures for sustainable geotechnical engineering solutions. The results of this analysis may form a basis for further investigation in that respect, hence the continued development and optimization of these materials toward long-term infrastructure resilience.

2. Methodology

The step-by-step process through which the data collection and analysis of sand–rubber tire shred mixtures for geotechnical engineering applications have been carried out is explained in this section. These include demonstrating the source of the data and the search strategy, the process of screening for document selection, and the criteria used in selecting the final dataset for bibliometric analysis.

2.1. Source and Search Strategy of Data

The bibliometric analysis was performed using data retrieved from the Scopus database. Scopus is one of the largest and most reliable sources of peer-reviewed literature data [43,44]. The Scopus database has been preferred for data collection in various research areas due to its large number of academic journals, conference proceedings, and other forms of scholarly outputs. It was also favored since its metadata features are highly extensive and relevant in bibliometric analyses [36]. The bibliometric analysis in this paper identified the trends, patterns, and structures of knowledge accumulation in the field of sand–rubber tire shred mixtures for geotechnical engineering applications. Bibliometric analysis is a powerful quantitative approach to analyzing large datasets of scientific publications by integrating data mining, mapping techniques, and statistical analysis. This method allows for the exploration of research trends, collaboration networks, and citation patterns. This paper used Scopus as the principal database because it covers comprehensive research areas in Engineering, Materials Science, Environmental Science, and Earth and Planetary Sciences, which generally have been identified to be relevant in understanding geotechnical applications of sand–rubber mixtures. The keywords of the search were: (“Sand-rubber” OR “Sand-rubber Mixture” AND “Geotechnical Engineering Applications”). These keywords were chosen because they represent all aspects of the sand–rubber applications, from material characterization to practical applications in geotechnical engineering. The total number of documents extracted in the initial search was 573, published between 1978 and 2025. This collection, after verification that the set had no duplicates, formed the base for the succeeding steps of selection. The search strategy was conducted in such a way that all the documents that were related to the keywords were reflected, while at the same time avoiding unnecessary elimination of subfields. During this step, no filtering on document type, language, or form of publication was conducted to diversify. That is, studies would be selected to the highest possible extent for further refinement of the dataset by the inclusion and exclusion criteria as outlined in subsequent sections. This approach ensures that large-scale studies are not missed during the initial search.

2.2. Screening

The dataset underwent multistep screening for relevance and quality, as represented in Figure 1. The initial retrieval of documents successfully reached 573. First was the application of a time-based filter—the selected studies had to be implemented between the years 2000 and 2025—reducing this number to 490 documents. Such a time frame was chosen to focus on the most recent research and developments within the field. Indeed, the sand–rubber tire shred mixtures in geotechnical engineering applications have drastically changed in recent decades. This query reduced the dataset to 490 documents. Hence, this step, carried out during this current work, ensured that only studies from relatively recent years were considered relevant to current scientific and industrial practices. The next criterion entailed filtering by subject areas. Subject area filtering was utilized to ensure relevance and accuracy for the bibliometric analysis. The filtering of data resulted in a limitation to core domains. Records outside the core subject areas relevant to the study were further filtered out. The following fields were excluded: Computer Science, Social Sciences, Medicine, Mathematics, Business, and Health Professions. The resultant dataset consisted of 447 documents related to Engineering, Materials Science, and Environmental Science. Filtering by source type was the next step of the selection process.

Only documents published in academic journals and conferences went into bibliometric analysis. Other than that, documents such as book chapters, conference reviews, and errata have been excluded in this filtering. This leaves the dataset with 437 documents. This reflected that peer-reviewed articles have more consistent and reliable information on the field. In addition, the publications were further screened to English-language documents for ease of access and consistency, thus reducing the dataset to 396 documents. Finally, documents published in book series were excluded, which resulted in a final dataset of 366 documents that could be used for bibliometric analysis. This is, therefore, a screening for contributions that focuses only on peer-reviewed and research-based information to contribute to scientific knowledge about the sand–rubber tire shred mixtures in geotechnical engineering applications. This inclusion normally contains a fully fledged study with all the details of methodology, results, and discussions, hence, more capable of bibliometric analyses, unlike other document types.

2.3. Selection of Data for Bibliometric Analysis

Data extraction and filtering were thus conducted to include only those of high quality and relevance after the dataset had been finalized. Bibliometric data were exported from the Scopus database in CSV format and analyzed using VOSviewer version 1.6.19 to construct co-authorship, co-occurrence, and citation networks. The full counting method was adopted to provide a balanced representation of authors’ and countries’ contributions. For each analysis type, appropriate minimum occurrence thresholds were determined in accordance with standard bibliometric practice to ensure clear and interpretable network visualization, thus providing insights into trends in research and collaborative efforts concerning geotechnical applications of sand–rubber mixtures. Moreover, network normalization was performed using the association strength method, which is the default and widely adopted approach in VOSviewer.

A document-by-document metadata review assured the quality of the dataset, with only research fitting into the objectives of the study being considered. Only documents with relevant keywords in either the title, abstract, or keywords were retained to ensure a quality dataset. This final dataset comprises 366 documents that have been used as the basis for further bibliometric analysis, visualizing the research developments in the field of sand–rubber mixtures in geotechnical engineering. Figure 1 presents the process flow diagram of the systematic approach adopted in the bibliometric study of the sand–rubber tire shred mixtures for geotechnical engineering applications from 2000 to 2025.

3. Results and Discussion

3.1. Publication Trends

Figure 2 presents a trend of an annual increase in publications on mixtures of sand and rubber tire shreds as a continuous development, especially after 2015. This is combined with the latest developments in world interest in topics related to a circular economy or sustainable construction materials, remarked on by authors such as [45], because re-using used tires is very critical for solving certain environmental and engineering problems. This increase also corresponds to the advancement in more effective testing methodologies and numerical modeling techniques, as mentioned by [46], which gave ways of better determinations of mechanical and durability properties of the mixtures of sand and rubber.

The spike in 2022–2023 could be the product of several fundamental studies conducted in earlier years. Most research on geotechnical applications during this period, by contrast, focused on specific applications where substantial benefits were evident, such as retaining wall backfill [47] and vibration isolation layers [48]. While the number of publications in 2023–2024 is slightly lower, the decrease is not substantial, and the overall trend still shows a steady increase in research activity within this field.

3.2. Document Type Distribution

The fact that 82% of the documents are journal articles reflects the strong empirical basis for research in this area. Usually, peer-reviewed journal articles may report comprehensive investigations, including experimental, analytical, and numerical studies. Several seminal papers, such as [4,49], are concerned with an optimization approach based on the improvement of particle size distribution and tire shred proportion through the enhancement of mechanical properties such as shear strength and compressibility.

This reflects that a smaller percentage of conference papers are 18%, and therefore researchers prefer to publish mature findings rather than preliminary results. On the other hand, conference proceedings have played an important role in disseminating new applications and testing methodologies; for instance, using sand–rubber mixtures for seismic isolation or embankment stability was reported by [50]. The trend therefore seems to be in obtaining robust and replicable data for practical advancement in the use of these materials.

3.3. Subject Area Distribution

Figure 3 demonstrates that the research into sand–rubber tire shred mixtures has an interdisciplinary nature. Accordingly, it is expected that engineering (mainly geotechnical and civil) and material sciences are the most dominating discipline, since the discussed material is of a technical nature. Research like those of [51,52] has addressed the mechanical behavior of sand–rubber mixtures under different conditions of stress, concentrating on their use for lightweight backfill, drainage layers, and vibration damping materials.

The significant share of environmental science reflects the field’s focus on sustainability. Rubber tire waste, a global pollutant, has been identified as a critical target for recycling efforts, as emphasized in studies like [53]. Sand–rubber mixtures are seen as a win-win solution, reducing waste and providing engineering benefits such as reduced bulk density, high energy absorption capacity, and resilience to dynamic loads. These findings support international commitments to waste management and resource conservation, such as those laid down in the United Nations Sustainable Development Goals.

Interestingly, the lower representations of physics, astronomy, agricultural sciences, and others show that there is also a wider, more general experimentation and practical application. For instance, sand–rubber mixtures were tested for erosion protection in agriculture uses [54], and in specific applications related to energy, with regard to thermal insulation properties [55]. These applications underpin the versatility of tire-derived aggregates outside the more traditional uses of naturally occurring geotechnical ones.

3.4. Journals Networking on Sand–Rubber Tire Mixtures

Figure 4 shows the journal network for research on sand–rubber tire mixtures for geotechnical engineering applications. Journals such as Wear, Construction and Building Materials, and Soil Dynamics and Earthquake Engineering have created high outputs in this field and have occupied central positions that might have a great influence on recent research trends. These are the high-link-intensity journals, meaning pivotal contributions have been made in advancing the knowledge in sand–rubber mixture aspects of mechanical properties, durability, and sustainability.

This is demonstrated by the fact that journals related to geotechnical, materials science, and sustainability aspects overlap with each other. Innovative applications of materials are presented in journals on surface and coating technology, while Tribology International and Geotechnical and Geological Engineering present various research on reinforcement techniques for soil. This networking would mean a milieu of collaboration that fosters research, innovation, and practical implementation of sand–rubber tire mixtures for different geotechnical purposes.

The growing relevance of journals such as the Journal of Cleaner Production and Sustainable Materials and Technologies underlines the shift in recent emphasis toward greener practices in geotechnical engineering. Such a journal provides valuable contributions to environmental benefit insights concerning the recycling of tire shreds, which further meets wider objectives of sustainable construction and waste reduction. Furthermore, more specialized journals like Soils and Foundations and Granular Matter deal with very specific geotechnical issues, such as settlement characteristics and the bearing capacity of sand–rubber mixtures, and hence drive targeted advancement in the field, as shown in

Table 1. The top 15 journals in sand–rubber tire mixtures for geotechnical engineering applications in terms of citation.

Journal	Cluster	Links	TLS	Documents	Citations	Avg. Citations
Wear	2	8	229	61	3081	50.5082
Surface and Coatings Technology	2	6	54	11	969	88.0909
Soil Dynamics and Earthquake Engineering	1	7	930	7	593	84.7143
Tribology International	2	6	101	6	428	71.3333
Geotechnical and Geological Engineering	1	7	685	5	353	70.6
Materials and Design	2	6	25	5	309	61.8
Materials Science and Engineering: A	2	6	23	5	292	58.4
Journal of Materials in Civil Engineering	1	7	648	7	152	21.7143
Granular Matter	1	7	614	6	120	20
Construction and Building Materials	1	8	462	5	112	22.4
Materials	1	13	323	11	103	9.3636
Materials Today: Proceedings	2	7	30	6	85	14.1667
International Journal of Geomechanics	1	8	949	6	67	11.1667
Geotechnical Special Publication	1	7	426	6	44	7.3333
Proceedings of the International Thermal Spray Conference	2	5	23	7	36	5.1429

.

Journal metrics and influence of the top productive journals ranking, shown in Table 1, relies on citation metrics, together with publication output, to rank the journals that have published on sand–rubber tire mixtures research. High average citations per article, such as those from Surface and Coatings Technology (88.09) and Soil Dynamics and Earthquake Engineering (84.71), are reflective of influential contributions. It is clear that the Wear journal boasts the highest number of total citations, 3081, with an average of 50.51 citations per publication, showing its emphasis on durability and the properties of wear of materials. Next, the Construction and Building Materials journal also stands high in the number of links and in total link strength, reflecting its importance as a bridge between geotechnical and structural applications. Following this, the Geotechnical and Geological Engineering journal provides ample illumination on the field of soil–structure interaction, averaging 70.6 citations per article, reflecting its high academic and practical value.

Interdisciplinary journals, such as Materials and Design and Materials Science and Engineering: A, present great contributions focused on the innovative applications and performance optimization of the mixtures of recycled tires. Specialized journals, such as the International Journal of Geomechanics and Environmental Geotechnics, emphasize understanding the long-term behavior, environmental implications, and mechanical stability of sand–rubber mixtures. These journals are very helpful in addressing issues concerning leachate potential, biodegradability, and geotechnical stability under varying conditions. Other emerging platforms like Materials Today: Proceedings and Granular Matter extend the landscape with focused studies on granular mechanics and the cyclic performance of materials. These contributions further create a comprehensive addition to findings from established journals that collectively drive innovation in sustainable geotechnical engineering solutions.

Hence, Figure 4 and Table 1 summarize the diversity and interconnectedness of research on sand–rubber tire mixtures in geotechnical engineering. The influential roles of core journals and their interdisciplinary collaborations have been strong in laying a foundation to further sustainable practices and innovative applications of materials in such fields. These insights are very helpful in bridging the gulf between theoretical advances and practical implementations, fostering more resilient and environmentally responsible construction practices.

3.5. Research Areas of the Sand–Rubber Tire Mixtures

The all-keyword network in Figure 5 shows three dominant research themes which are “rubber content,” “particle size,” and “grain size”. The centrality of these terms reflects extensive studies on how rubber shred geometry and sand–rubber ratios influence geotechnical properties. For example, “rubber content” has a strong affinity for “compressive strength”, in agreement with the findings of [56] that showed a rubber content higher than 30% by weight significantly reduces the shear strength in sand–rubber mixtures. While “particle size” clusters with “abrasion resistance”, this agrees with [57], who mentioned that coarser rubber shreds resulted in better wear resistance due to its interlocking characteristics with angular sand grains. However, the absence of “thermal conductivity” or “hydraulic permeability” shows the lack of studies dealing with the impact of rubber on the environmental functions of soil, such as landfill liners, which is a serious omission considering the low permeability of tire rubber [58].

The strong linkage between “damping ratio” and “rubber mixtures” underscores rubber’s viscoelastic properties, which dissipate seismic energy—a key advantage in liquefaction-prone regions [59]. However, the peripheral position of “earthquakes” suggests most studies focus on lab-scale dynamic testing rather than field validations. This contrasts with mature fields like base isolation systems, where full-scale rubber bearings are well-documented [60]. This may further be supported by the weak co-occurrence of “finite element method” and “seismic isolation,” which again hints that computational models play a minor role in predictions of large-scale infrastructure performance. Also, the strong appearance of “three-body abrasion” shows a growing interest in industrial applications such as machinery parts subjected to abrasive sand–rubber media (conveyor belts in recycling plants). Works such as [61] have investigated “tungsten carbide coatings” to reduce wear in sand–rubber composites; however, the niche positioning of “corrosion resistance” and “environment” indicates limited consideration of chemical degradation processes. This is of concern, as leachates from tire rubber, for example, zinc and sulfur, can cause corrosion of proximal materials and groundwater contamination [62].

Table 2. Top 39 keywords from the studies published on the sand–rubber tire mixture.

Keywords	TLS	Cluster	Occurrences
Wear	34	3	32
Shear Modulus	31	2	16
Microstructure	29	3	20
Abrasive Wear	28	1	46
Hardness	27	5	17
Hardfacing	26	6	23
Abrasion	23	5	19
Damping Ratio	23	2	14
Wear Resistance	19	1	22
Geosynthetics	16	2	8
Coating	15	1	6
Sand	15	4	16
HVOF	14	1	8
Heat Treatment	12	3	7
Sand–Rubber Mixtures	12	2	10
Particle-Scale Behavior	11	2	6
Three-Body Abrasion	11	5	12
Fabric/Structure of Soils	10	2	5
Granulated Rubber	10	2	6
WC-CO	10	1	6
Wear Testing	10	5	6
Discrete Element Method	9	4	8
Sand–Rubber Mixture	9	4	11
Sand–Rubber Mixtures	9	4	5
Tungsten Carbide	9	1	5
ASTM G65	8	1	7
Carbide	8	6	5
Damping	8	4	6
Mechanical Properties	8	1	6
Wear Mechanism	8	1	9
Rubber	7	4	7
Steel	7	3	5
Boron	6	3	5
Coatings	5	3	5
Shear Strength	5	4	7
Sliding Wear	5	5	5
Abrasion Resistance	4	3	7
Seismic Isolation	3	2	5
Abrasive Wear Resistance	1	6	5

presents the keywords that met or surpassed a predefined threshold for inclusion in the analysis. Specifically, the analysis focused on keywords provided by authors, rather than indexed keywords. The top 39 keywords are ranked in descending order based on their TLS. This ranking was determined through a comprehensive scientific analysis that considered factors such as cumulative link strength, the number of connections for each keyword, and their frequency of occurrence. By applying these criteria, we ensure that only the most relevant and impactful keywords are included in the study, allowing for a more robust and insightful analysis of the research landscape related to the sand–rubber tire mixture.

The keywords presented in Table 2 offer a comprehensive overview of the evolving research landscape surrounding sand–rubber tire mixtures. A total of 39 keywords were identified, reflecting a diverse range of research themes that converge on key aspects of material science, engineering, and environmental sustainability. Among these, terms such as “Wear,” “Abrasive Wear,” “Microstructure,” and “Damping Ratio” frequently appear, indicating their critical roles in understanding the performance and applicability of these composites. “Wear” emerges as the most prominent keyword, with the highest TLS of 34, underscoring its centrality in discussions about the durability and longevity of sand–rubber mixtures across various applications. The frequent mention of “Abrasive Wear” highlights the challenges these materials face under mechanical stress, particularly in industrial settings where wear resistance is crucial. This focus on wear mechanisms is essential for developing strategies to enhance the lifecycle of products made from these materials, which is vital in both economic and environmental contexts.

Additionally, the emphasis on mechanical properties, exemplified by keywords such as “Shear Modulus,” “Hardness,” and “Shear Strength,” illustrates a concerted effort to quantify how these materials behave under different loading conditions. Understanding these properties is essential for optimizing the design and application of sand–rubber mixtures in construction, automotive, and other industries. The interconnectedness of these keywords suggests a holistic approach to material development, where performance metrics directly inform design choices.

The presence of keywords related to testing methodologies, such as “Wear Testing” and “Discrete Element Method,” underscores the importance of empirical validation in this research area. Advanced analytical techniques are becoming increasingly vital for accurately assessing material behavior and informing future innovations. This emphasis on rigorous testing reflects a growing recognition that theoretical models must align with practical outcomes, thereby enhancing the reliability and applicability of research findings.

Likewise, the keywords authors assigned to Figure 6 focus on methodological and material science issues and are computational modeling (“finite element method”, “discrete element modeling”). The dominance of computational terms reflects the field’s reliance on numerical simulations to predict complex sand–rubber interactions. For instance, ref. [63] utilized DEM in order to model the development of shear bands in the course of rubber-reinforced soils and replicated the lab results with <5% error. However, the absence of “machine learning” or “AI” in author keywords suggests computational approaches remain traditional, lagging adjacent fields like polymer science, where AI-driven material design is thriving.

In the diagram shown in Figure 6, the nodes symbolize different elements, and their shapes and positions indicate the probability of co-occurrence among these elements. Analyzing the keyword co-occurrence network reveals six distinct clusters, each represented by unique colors, corresponding to various topics within the realm of the sand–rubber tire mixture. The colored nodes represent these clusters, with each focusing on a specific area within this field. The size of the nodes reflects their frequency of occurrence, while the thickness of the connections between them demonstrates the strength of their relationships.

The first cluster, represented in (red), centers on wear and resistance. The prominence of keywords like “Wear,” “Abrasive Wear,” and “Wear Resistance” signals a significant focus on the durability of sand–rubber mixtures. This cluster highlights the necessity of developing materials capable of withstanding abrasive conditions, particularly in applications where material degradation can lead to failures or safety concerns. Ongoing research in this area aims to create solutions that extend product lifespan and enhance performance, which is essential in industries such as construction and automotive engineering.

The second cluster, represented in (green), shifts attention to mechanical properties. Keywords such as “Shear Modulus,” “Hardness,” “Damping Ratio,” and “Shear Strength” underscore the critical importance of understanding the mechanical behavior of these mixtures. This focus is especially relevant in applications requiring energy absorption and vibration dampening, where material performance can significantly influence safety and functionality. The interconnectedness of these properties suggests that optimizing one aspect can lead to improvements in others, reinforcing the need for a comprehensive approach to material design.

In the third cluster, represented in (blue), the focus broadens to material composition and structure. Keywords like “Microstructure,” “Granulated Rubber,” and “Coating” indicate a deep interest in how the arrangement of rubber particles and sand affects overall performance. Studying microstructure is crucial for developing composite materials that achieve desired mechanical and physical properties. Additionally, the mention of coatings suggests innovative strategies for enhancing durability and performance, indicating a move towards multifunctional materials that can provide both structural integrity and specialized surface characteristics.

Moving to the fourth cluster, represented in (yellow), we observe an emphasis on testing and methodology. Keywords such as “Discrete Element Method,” “HVOF” (High-Velocity Oxygen Fuel), and “Heat Treatment” underscore the advanced experimental techniques employed to study sand–rubber mixtures. Incorporating sophisticated modeling approaches like the Discrete Element Method facilitates a more nuanced understanding of material behavior at the particle level, enabling simulations that can predict performance under various conditions. This methodological rigor not only enhances the reliability of research outcomes but also supports the development of more targeted and effective material formulations.

The fifth cluster, represented in (purple), highlights applications and environmental impact. Keywords such as “Geosynthetics” and “Damping” suggest practical uses of sand–rubber mixtures in construction and environmental engineering. Utilizing recycled materials, such as rubber, in geosynthetics reflects a growing commitment to sustainability and resource efficiency. This cluster emphasizes the dual goals of enhancing structural performance while addressing environmental concerns, showcasing a holistic understanding of how material choices can impact both economic and ecological outcomes.

Finally, the sixth cluster, represented in (light blue), represents emerging trends and innovations. Keywords like “Three-Body Abrasion,” “Particle-Scale Behavior,” and “Sand” indicate a focus on cutting-edge research directions within the field. The attention to “Three-Body Abrasion” suggests an interest in refining testing methods to better understand wear processes, while “Particle-Scale Behavior” highlights a trend toward investigating fundamental interactions at the microscopic level. This research area holds significant potential for uncovering new insights that could lead to breakthroughs in material properties and applications.

The cluster around “hardfacing alloys” delineates efforts invested in enhancing the wear properties of the sand–rubber composite. Very recently, ref. [64] reported enhanced abrasion resistance by 40% in plasma-sprayed “alumina coatings” used in sand–rubber mixes for railway ballast. However, the loose link between “coatings” and “cost analysis” infers limited studies pertaining to economic viability—a barrier before industrial acceptance. Strikingly, “circular economy”, “lifecycle assessment”, and “carbon footprint” are absent, despite global policies mandating sustainable construction practices (EU Waste Framework Directive 2008/98/EC). Author priorities here reflect a persistent engineering focus on performance over environmental holism—a trend requiring correction to align with UN Sustainable Development Goals (SDG 11 and 12).

Figure 7 shows the network visualization of the most frequent keywords appearing in research related to sand–rubber tire mixtures for geotechnical engineering applications. Indexed keywords in Figure 7 standardize the terminology, showing alignment to larger scientific domains: materials science integration (“composite materials,” “mechanical properties,” “abrasion tests”). Interdisciplinary efforts to hybridize the mixtures of sand–rubber with industrial-grade additives are represented by the combination of geotechnical and materials science keywords—for example, “silicon carbide,” “tungsten alloys.” For example, ref. [65] has shown that “crumb rubber” addition enhances flexural strength by up to 22% and thus allows application in pavements. The weak connection between “composite materials” and “field trials” underlines a translational gap in research.

The strong cluster around “shear strength” validates rubber’s role in enhancing soil ductility, as shown by [59] in liquefaction mitigation. Yet, the absence of “long-term aging” or “UV degradation” in indexed keywords raises concerns about the durability of sand–rubber mixtures in exposed environments—a critical oversight given rubber’s susceptibility to photochemical breakdown [66].

Collaboration with environmental chemists might help to evaluate the leaching toxicity (such as zinc from rubber), while economists could assess cost–benefit ratios for developing countries that lack waste management infrastructure. Hence, keyword networks confirm sand–rubber tire mixtures as a vibrant interdisciplinary area of research with sound underpinning in geotechnical mechanics and material science. On the other side, the absence of sustainability-centric terminology and the corresponding translational research bring an urgent signal for reorientation toward the principles of the circular economy. These lacunae indicate a different trajectory to take this area from niche laboratory studies to mainstream policy-driven applications, where tire wastes change from an environmental liability into a geotechnical asset.

Overall, the analysis of these keywords reveals a rich and interconnected research landscape concerning sand–rubber tire mixtures. The emphasis on mechanical properties, innovative testing methodologies, and environmental considerations indicates a commitment to developing materials that are both durable and sustainable. As the field progresses, future research is likely to focus on optimizing these properties, exploring advanced manufacturing techniques, and expanding the applications of sand–rubber mixtures across various industries, ultimately contributing to a more resilient and sustainable material future.

3.6. Countries Leading the Sand–Rubber Tire Mixtures

Figure 8, Figure 9 and Figure 10 demonstrate the global structure of research collaboration in sand–rubber mixtures for geotechnical engineering applications and indicate the most productive countries in terms of the subject matter of the documents. China and India have emerged as the most productive contributing countries, each publishing 57 documents. This dominance reflects their rapid industrialization, burgeoning infrastructure demands, and acute challenges in managing end-of-life tires, which account for over 1.5 billion units discarded globally annually [67]. China’s leadership aligns with its “Circular Economy Promotion Law,” which prioritizes tire recycling, while India’s output stems from initiatives like the Swachh Bharat Mission, emphasizing sustainable waste-to-resource conversion [68]. Brazil comes next with 30 documents, and Iran with 29 documents, which are mainly driven by geotechnical needs in seismically active regions and urban expansion projects needing lightweight, cost-effective fill materials [59].

On the other hand, European countries such as the UK (27 documents) and Germany (12 documents) have focused their efforts more on advanced applications like seismic isolation systems, reflecting stringent EU sustainability directives 2008/98/EC, together with a well-settled research infrastructure. The meager contributions from African countries, such as Nigeria and South Africa, with ≤2 documents, testify to systemic inequalities in funding and technical capacity, at variance with dire tire waste situations in these parts of the world—a concern which [69] point out in their discussion of Global South recycling practices. The geographical skew here reflects broader trends within research into recycled materials, where policy frameworks and industrial priorities have come to shape regional outputs [70].

The co-authorship network in Figure 10 defines three regional clusters, each with its thematic foci. Cluster 1 (India, Brazil, Canada) prioritizes tropical and temperate applications, exemplified by India’s studies on sand–rubber mixtures for monsoon-resilient roadways [71] and Brazil’s work on landfill liners using tire shreds—a response to its 2019 National Solid Waste Policy. Cluster 2 (China, Hong Kong, Iran) focuses on dynamic behavior and large-scale infrastructure, such as the use of soil–rubber composite materials in high-speed rail embankments in China, a project in line with its Belt and Road Initiative [72]. Cluster 3: Poland, Croatia, Argentina—Industrial applications, including abrasion-resistant coatings, are often supported by EU Horizon grants for sustainable materials.

Collaboration patterns mapped in Figure 10 and quantified in

Table 3. Leading 25 countries through collaboration publishing on the sand–rubber tire mixtures for geotechnical engineering applications (ranked by total link strength (TLS)).

Country	Cluster	Links	TLS	Documents	Citations	Avg. Citations
Hong Kong	2	19	9453	22	897	40.7727
India	1	24	7332	57	1338	23.4737
Iran	2	22	6972	29	554	19.1034
China	2	24	6794	57	1316	23.0877
United Kingdom	2	23	4677	27	895	33.1481
Australia	2	23	3815	18	450	25
Greece	2	22	3372	9	820	91.1111
United States	2	21	2847	25	645	25.8
France	2	23	2041	12	370	30.8333
Germany	1	22	1818	12	503	41.9167
Turkey	1	20	1413	9	250	27.7778
Poland	3	21	1338	9	155	17.2222
Algeria	2	18	1255	5	74	14.8
South Korea	2	18	898	6	545	90.8333
Spain	2	22	814	5	131	26.2
Canada	1	22	771	15	389	25.9333
Brazil	1	24	708	30	434	14.4667
Italy	1	14	502	5	480	96
Finland	1	19	494	8	405	50.625
Czech Republic	1	22	340	12	238	19.8333
Colombia	1	20	270	8	492	61.5
Malaysia	1	19	158	5	88	17.6
Thailand	1	10	72	5	32	6.4
Croatia	1	12	35	8	8	1
Argentina	1	10	33	5	210	42

show that Hong Kong is the most connected hub, with a TLS of 9453, reflecting its partnerships with mainland China but also with institutions such as the Hong Kong Polytechnic University—an early leader in developing soil–rubber composites for landslide mitigation [60]. India (TLS = 7332) and Iran (TLS = 6972) are regional anchors that develop cross-border collaborations on low-cost embankment solutions, a key need for flood-prone and earthquake-vulnerable areas in Asia. Ref. [56] report exceptionally high average citation impact for Greece and South Korea—91.1 and 90.8, respectively, despite their modest document counts, reflecting a niche focus on high-impact topics. For example, Greek research into the damping properties of rubber for earthquake-resistant infrastructure [59] and South Korean innovations in tungsten carbide coatings for wear-resistant composites [61] have received international acclaim. By contrast, the relatively low citation metrics for Brazil (Avg. citations = 14.5) reflect a more applied focus on finding localized solutions to problems, such as using materials in road base, which meets near-term infrastructure needs but is less visible globally.

The commanding position of Asian and Middle Eastern nations points to the interrelatedness of policy, industrialization, and environmental needs in sand–rubber tire research. While the Chinese “Zero Waste Cities” initiative and the Indian Smart Cities Mission (ISCM) have catalyzed this innovation in recycling tires, their focus on mechanical performance has more often than not sidetracked ecological concerns. Conversely, European research, though less voluminous, integrates lifecycle assessments and circular economic metrics to evaluate carbon footprints of rubber-enhanced slopes. Future efforts must reconcile these regional disparities by fostering South–South partnerships, such as India–Brazil collaborations on tropical soil stabilization, and North–South knowledge exchanges to address the tire waste challenges. It is expected that, as this area matures, regional priorities in line with the UN SDGs 9 (Industry, Innovation, Infrastructure) and 11 (Sustainable Cities) will drive the transition from the environmental burden of waste tires to geotechnical assets.

4. Sand–Rubber Tire Mixtures for Geotechnical Engineering Applications

Table 4. Overview of sand–rubber tire shred mixtures’ studies in geotechnical applications for the last 1-years.

Title	Type of Sand and Rubber Used	Mixing Ratio	Geotechnical Application	Main Findings	Advantages	Limitations	Year	Ref.
Performance of Geocell-Reinforced Rubber–Sand Mixtures	Sand and rubber (425 μm to 12 mm)	10–40% rubber by volume	Load-bearing capacity in geotechnical structures	Improved shear strength with increasing rubber size and confining pressure	High energy absorption for seismic loads	Limited efficiency at low rubber content	2024	[75]
Effect of Tire-Rubber Inclusion on The Physical and Mechanical Behavior of Granular Soils	Fine granular soil and tire shreds	Various rubber-to-sand ratios	Soil stabilization and compaction	Optimal rubber geometry enhances shear strength and void ratio	Improved compaction efficiency	High anisotropy affects mechanical properties	2024	[76]
Sand–Rubber Mixtures under Oedometric Loading	Sand and rubber chips of various sizes	Various ratios based on density and void saturation	Embankment stabilization, retaining wall backfill	High deformability of rubber-rich mixtures, rubber-like or sand-like behavior classification	Enhanced compressibility control	Void saturation leads to loss of sand-like behavior	2023	[23]
Sand–Tire Shred Mixture Performance in Controlling Surface Explosion Hazards	Sand and tire shreds	10%, 20%, 30% rubber by weight	Blast energy dissipation for underground structures	Effective energy dissipation, but depends on mixture thickness	Increased structural protection	Ineffective in thin layers	2021	[22]
Engineering Properties of Sand–Rubber Tire Shred Mixtures	River sand and fine rubber tire shreds	Various controlled proportions	Shear behavior, compressibility, and drainage characteristics	Increase in rubber content reduces shear strength and increases compressibility	Ductility enhancement and energy absorption	Reduction in shear strength and permeability	2021	[4]
Strength and Deformation of Sand–Tire Rubber Mixtures (STRM)	Sand and granulated rubber	0–50% rubber by weight	Highway embankments, retaining wall backfill	Optimal shear strength at 10–20% rubber content, decreasing beyond 30%	Enhances ductility and stress–strain behavior	High rubber content leads to lower stress ratio	2019	[77]
An Investigation on the Shear Strength Parameters of Sand–Rubber Mixtures	Sand and granulated rubber/rubber chips	30% rubber by weight	Road embankments and backfills	Higher friction angle with chip rubber than with sand alone	Improved load distribution	High rubber content reduces stiffness	2018	[78]
The Direct Shear Strength of Sand–Tire Shred Mixtures	Sand and tire shreds	Various proportions	Lightweight structural fill	Increased shear strength with optimal tire shred content	Cost-effective fill material	High variability in behavior	2015	[73]
Direct Shear Tests on Waste Tires–Sand Mixtures	Fine angular sand, coarse rotund sand, and shredded waste rubber	5%, 10%, 20%, and 50% by dry weight	Shear strength and internal friction analysis	Increase in rubber decreases shear strength and internal friction angle	Lightweight fill material	Decrease in shear strength at high rubber content	2011	[74]
Interaction of Ribbed-Metal-Strip Reinforcement with Tire Shred–Sand Mixtures	Tire shreds of different sizes and sand	0%, 12%, 25%, 100% by weight	MSE wall backfill material	Higher pullout capacity in mixtures than in pure tire shreds	Improved reinforcement properties	Variability in tire shred sizes affects consistency	2010	[79]

presents a comprehensive review of the geotechnical applications of sand–rubber tire shred mixtures, highlighting their effectiveness in soil stabilization, reinforcement, and structural applications. The studies included span from 2010 to 2024, showcasing various experimental methodologies, material compositions, and performance outcomes. A common theme across these studies is the evaluation of shear strength, compressibility, and deformation characteristics of sand–rubber mixtures. The research by [4] indicates that increasing rubber content in sand mixtures results in reduced shear strength and permeability while improving ductility and energy absorption. These findings align with prior studies such as those by [73,74], who observed similar trends in reduced friction angle and shear resistance with increased rubber content. This suggests a trade-off between mechanical stability and enhanced deformation properties, which could be beneficial in applications requiring energy absorption, such as seismic isolation.

A significant observation from the reviewed studies is the variation in rubber-to-sand mixing ratios and their influence on geotechnical behavior. For instance, ref. [77] found that shear strength improved at 10–20% rubber content but declined beyond 30%. Similarly, ref. [23] classified mixtures as sand-like or rubber-like based on void ratio variations, demonstrating that rubber fraction plays a crucial role in defining material behavior. These results are supported by [75], who noted that sand–rubber mixtures with 30% rubber exhibited optimal load-bearing capacity. These findings highlight the importance of determining optimal rubber content for different engineering applications, as excessive rubber may compromise shear strength, while too little rubber might not provide adequate energy dissipation.

One critical aspect of geotechnical engineering applications is the ability of sand–rubber mixtures to serve as lightweight fill materials, particularly in backfill and embankment projects. The study by [79] demonstrated that tire shreds, when used as part of mechanically stabilized earth (MSE) walls, significantly improved pullout resistance when mixed with sand. Similarly, ref. [76] highlighted how the geometric configuration of rubber particles influences soil compaction and mechanical behavior. These findings are in line with earlier works by [80], who noted that waste rubber inclusion improved soil cohesion while maintaining reasonable compaction characteristics. This suggests that sand–rubber mixtures can be effectively used in embankments, retaining walls, and slope stabilization projects, offering both environmental and economic benefits.

Beyond structural applications, sand–rubber mixtures have been explored for their potential in mitigating environmental hazards and energy absorption during dynamic loads. The research by [22] demonstrated that properly selected sand–rubber mixtures could reduce peak blast pressures in explosion-prone environments. Similar findings were reported by [4] in seismic isolation applications, where 10% rubber content provided the optimal damping properties for low-rise buildings. These studies align with previous work by Hazarika et al. (2010) [59], who found that sand-mixed tire chips significantly mitigated earthquake-induced vibrations. This indicates that sand–rubber mixtures are viable materials for impact-resistant and seismic applications, particularly in regions prone to natural disasters.

Despite these advantages, several limitations must be considered when using sand–rubber mixtures in geotechnical engineering. The study by [78] found that rubber inclusion increased compressibility and reduced stiffness, which can be detrimental in load-bearing applications. Similarly, ref. [81] noted that dynamic properties, such as shear modulus and damping ratio, varied significantly with rubber particle size and content. These findings are supported by [82], who observed that rubber inclusion improved ductility but compromised stiffness and ultimate resistance. These results emphasize the need for careful engineering design to balance the benefits of energy absorption and weight reduction against potential drawbacks in shear strength and structural stability.

Overall, the literature supports the use of sand–rubber tire shred mixtures in various geotechnical applications, particularly in lightweight fill, backfill, seismic isolation, and impact mitigation. The reviewed studies confirm that optimal rubber content is critical to achieving desired mechanical performance, and that geometric factors such as particle size and shape play a vital role in determining overall behavior. Future research should focus on long-term field performance, durability, and environmental impacts to further refine the applicability of these materials in large-scale infrastructure projects. These findings contribute to the growing body of knowledge on sustainable geotechnical materials and emphasize the potential for waste rubber reuse in engineering applications.

5. Limitations and Future Works

5.1. Limitations

Despite the promising results of sand–rubber mixtures in geotechnical applications, several limitations need to be addressed to ensure their effective and widespread utilization. One of the most significant limitations is the decrease in shear strength and stiffness when the rubber content exceeds 30–40%, which can negatively impact the stability and load-bearing capacity of structures relying on these mixtures.

Additionally, material heterogeneity and variability in rubber particle size, shape, and distribution can lead to inconsistencies in mechanical behavior, making it challenging to maintain uniform performance across different projects. Another critical issue is the difficulty in compaction and density control, as rubber materials are highly deformable and elastic, which can hinder proper compaction and lead to undesirable settlement over time. Furthermore, long-term durability concerns related to rubber degradation need further investigation to ensure sustainable environmental use. The potential water absorption of rubber particles also raises concerns about variations in drainage characteristics and permeability, which can affect the long-term stability of soil–rubber systems. Moreover, a significant limitation is the language bias inherent in the research, as studies published in languages other than English may be overlooked. This may result in the omission of relevant work indexed under different terms.

These challenges highlight the need for comprehensive studies and engineering guidelines to optimize the use of sand–rubber mixtures in geotechnical applications.

5.2. Future Works

Future research should focus on refining the material properties, mixing techniques, and design methodologies to maximize the efficiency and effectiveness of sand–rubber mixtures in geotechnical engineering. Large-scale field studies and long-term performance evaluations should be conducted to validate laboratory findings and assess the real-world behavior of these mixtures under different environmental conditions. Additionally, further investigations into the environmental impact of soil–rubber interactions, particularly in terms of leaching and biodegradability, will be necessary to ensure sustainability and compliance with environmental regulations. Developing innovative compaction techniques and reinforcement strategies, such as incorporating geosynthetics or stabilizing additives, could help mitigate the limitations associated with rubber’s high compressibility and low stiffness. Future work should also explore the potential of hybrid mixtures that combine sand, rubber, and other recycled materials to achieve improved mechanical performance while promoting circular economic principles. Finally, the establishment of standardized design codes and engineering guidelines will be essential to facilitate the practical adoption of sand–rubber mixtures in large-scale infrastructure projects, ensuring consistency, safety, and cost-effectiveness in their application.

6. Conclusions

This bibliometric analysis examined 366 articles on sand–rubber tire mixtures in geotechnical applications published from 2000 to 2025. The findings reveal a significant rise in publications, particularly after 2015, reflecting a growing interest in sustainable materials and heightened environmental concerns. Notably, 82% of these publications are peer-reviewed journal articles, indicating a robust empirical foundation, while 18% consist of conference papers that focus on innovative methodologies.

Research in this field predominantly spans geotechnical and civil engineering, with substantial contributions from environmental science, underscoring the importance of recycling tire waste for sustainability. Influential journals such as “Wear” and “Construction and Building Materials” play central roles in advancing knowledge, promoting collaboration and innovation within the research community. Leading countries like China and India are the top contributors, focusing on optimizing rubber content and exploring the dynamic behavior of these mixtures for infrastructure applications. In contrast, European nations emphasize advanced sustainability practices aligned with stringent environmental directives.

The literature supports the effective use of sand–rubber mixtures in applications such as lightweight fill, seismic isolation, and impact mitigation, with optimal rubber content being crucial for balancing mechanical performance. However, challenges remain, including compaction issues and variability in mechanical properties due to rubber particle size and distribution. While extensive laboratory studies have been conducted, large-scale field applications are still limited, highlighting the need for standardization of design guidelines and comprehensive durability assessments.

Future research should aim to optimize rubber content and particle geometry to achieve a balance between mechanical performance and environmental sustainability. The development of machine learning models for predictive analysis and numerical simulations could enhance our understanding of how sand–rubber mixtures behave under various loading conditions. Collaboration between academia and industry is essential to bridge the gap between theoretical research and practical implementation, ensuring these mixtures can become integral to sustainable geotechnical solutions. Ultimately, this study consolidates the evolution of sand–rubber tire shred research and underscores the potential of these materials to support circular economy principles by transforming waste tires into functional geotechnical applications. Continued research and development in this area are crucial for unlocking the full potential of sand–rubber mixtures and addressing the existing limitations of these innovative materials.