Arjun Murali

From a geotechnical engineering viewpoint, recycling and reuse of crushed glass and tire rubber can significantly help reduce the demand for natural resources (i.e., sand and gravel aggregates). Following an earlier study by the authors aimed at characterizing gravel–rubber mixtures (GRM), this paper focuses on the geotechnical assessment of gravel–glass–rubber mixtures (GGRM) made of recycled crushed green glass bottles and recycled granulated tire rubber. Specifically, the compaction, one-dimensional compressibility, and shear strength characteristics of GGRM prepared at 40% and 55% rubber content by volume (R_B) with varying glass content by volume (G_L) are investigated. It is found that compacted GGRM possesses high strength (i.e., friction angle ≥ 30°) and adequate compressibility, making it a suitable general and structural fill material for use in eco-friendly geotechnical applications.

Shredded rubber from waste tyres has progressively been adopted in civil engineering due to its mechanical properties, transforming it from a troublesome waste into a valuable and low-cost resource within an eco-sustainable and circular economy. Granular soils mixed with shredded rubber can be used for lightweight backfills, liquefaction mitigation, and geotechnical dynamic isolation. Most studies have focused on sand-rubber mixtures. In contrast, few studies have been conducted on gravel-rubber mixtures (GRMs), primarily involving poorly-graded gravel. Poorly-graded gravel necessitates selecting grains of specific sizes; therefore, from a practical standpoint, it is of significant interest to examine the behaviour of well-graded gravel and shredded rubber mixtures (wgGRMs). This paper deals with wgGRMs. The results of drained triaxial compression tests on wgGRMs are analysed and compared with those on GRMs. Stress-strain paths toward the critical state and energy absorption properties are evaluated. The tested wgGRMs exhibit good shear strength and remarkable energy absorption properties; thus, they can be effectively utilised in several geotechnical applications.

End-of-life tires (ELTs) are tires, unusable in their original form, which go into a waste management scheme (for recycling and energy recovery purposes), or otherwise are disposed. In New Zealand, the annual disposal of 3.5 million ELTs is posing critical environmental and socio-economic issues, and the reuse of ELTs through large-volume recycling engineering projects is a necessity. In this study, gravel and recycled granulated rubber were mixed to explore the possibility of obtaining synthetic granular geomaterials (with adequate geotechnical and environmental characteristics) that are suitable as structural fills for geotechnical applications including foundation systems for low-rise light-weight residential buildings. Moreover, an original framework with a set of geo-environmental criteria is proposed for the acceptance of gravel–rubber mixtures (GRMs) as structural fills. It is shown that when gravel-size like rubber particles are used, GRMs with volumetric rubber content of 40% or less have adequate strength (ϕ’ > 30°), low compressibility (ε_v ≤ 3%), excellent energy adsorption properties, and acceptable leachate metal concentration values (e.g., Zn < 1 mg/L), making them ideal synthetic structural fill materials for many sustainable geotechnical applications.

End-of-life tires (ELTs) represent a great source of readily available, low-cost and sustainable construction materials having excellent engineering properties. Their reuse (in the form of granulated rubber mixed with soils) in large-volume recycling civil (geotechnical) engineering applications would be beneficial and should be encouraged. It is estimated that at present worldwide only less than 10% of ELTs are reused in geotechnical applications, while nearly 40% are recycled as tire-derived fuel. Although many studies have focused on the material characterization of soil-rubber mixtures (SRMs), it appears that the results of such investigations have not been properly compiled and compared, making it difficult to fully understand the potential applicability of SRMs. In an attempt to provide useful insights facilitating the use of SRMs as geotechnical construction materials, this review paper presents a comprehensive review of published research on the engineering properties of granular soils (i.e., mainly sand and gravel) blended with various recycled rubber inclusions. Available experimental data are scrutinized, and the results of the analyses are presented and discussed primarily in terms of effects of rubber content and aspect ratio (ratio of rubber to gravel median particle sizes) on compaction, permeability, strength and compression properties along with dynamic and cyclic deformation characteristics of SRMs. This review paper may help to alleviate the concerns of designers and consumers and encourage and further promote the use of recycled rubber tires on a larger scale in civil engineering projects.