Search Results (6)

The accumulation of end-of-life tires and the rapid increase in demolition activities pose significant environmental and waste-management challenges. The redevelopment of construction materials incorporating this waste is a potentially promising strategy for minimizing environmental impact while promoting the principles of a circular economy. This study investigates the performance of self-compacting concrete (SCC) incorporating up to 20% rubber aggregates (sand and gravel) and 40% recycled concrete aggregate (RCA) for non-structural applications. A series of tests was conducted to assess fresh and hardened properties, including flowability, compressive strength, tensile strength, flexural strength, water absorption, and density. The results indicated that increasing RCA content reduced density and compressive strength, while tensile and flexural strengths were only moderately affected. Response surface methodology (RSM), utilizing a Box–Behnken design, was employed to optimize compressive, tensile, and flexural strength responses. Statistical analysis was used to identify the optimal mix proportions, which balance the mechanical performance and sustainability of SCC with recycled components. Mixtures incorporating moderate rubber content—specifically, 5–5.5% sand rubber and 0–6% coarse rubber—and 40% recycled-concrete aggregate (RCA) achieved the highest predicted performance, with compressive strength ranging from 20.00 to 28.26 MPa, tensile strength from 2.16 to 2.85 MPa, and flexural strength reaching 5.81 MPa, making them suitable for sidewalks and walkways. Conversely, mixtures containing higher rubber proportions (5.5–20% sand rubber and 20% coarse rubber) combined with the same RCA level (40%) showed the lowest mechanical performance, with compressive strength between 5.2 and 10.08 MPa, tensile strength of 1.05–1.41 MPa, and flexural strength from 2.18 to 3.54 MPa. These findings underscore the broad performance range achievable through targeted optimization. They confirm the viability of recycled materials for producing environmentally friendly SCC in non-structural applications. Full article

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. Full article

Within the scientific research project ‘RubSuPave’, a large number of laboratory tests were carried out to investigate the addition of waste rubber (WR) to mixtures of a cement-bound base course (CBC) for pavement construction. For mixtures consisting of gravel aggregate, sand, cement (at 3%, 5%, and 7% by mass) and various sand replacements with WR (0%, 10%, 20%, 30% and 40% volume) additions, the compaction characteristics, compressive strength, and resistance to freezing and thawing (F/T) were determined. The results show that compressive strength is negatively affected by the addition of WR, while F/T resistance is improved, with mixtures containing 10–20% WR and 5% cement being optimal. The next step was transferring the knowledge gained into field conditions via the large-scale production of such mixtures in concrete plants and the construction of test fields. The CBC reference and WR mixtures (2% mass) were produced in two different concrete plants; the samples were compacted, and compressive strength and F/T resistance were tested. The CBC mixtures made in the first plant were used for the construction of the test field. The results and problems of mixture production in two different concrete plants are presented, along with the experiences of the construction of a test field with such a rubberised base course. The in-plant production of mixtures with 2% WR also resulted in a reduction in compressive strength and improved resistance to freezing, but these significantly values varied between plants. The main reasons for this are that the addition of WR causes issues due to its dosing and during its incorporation into the second plant, difficulty in achieving a homogenous mixture, and the subsequent maintenance of the concrete plant, implying that the technology should be adapted for large-scale production in future. The test field, with both the reference mixture and the WR mixture from the first plant, will be monitored further to determine its behaviour in real conditions. Full article

Trafficability gives tracked vehicles adaptability, stability, and propulsion for various purposes, including deep-sea research in rough terrain. Terrain characteristics affect tracked vehicle mobility. This paper investigates the soil mechanical interaction dynamics between rubber-tracked vehicles and sedimental soils through controlled laboratory-simulated experiments. Focusing on Bentonite and Diatom sedimental soils, which possess distinct shear properties from typical land soils, the study employs innovative user-written subroutines to characterize mechanical models linked to the RecurDyn simulation environment. The experiment is centered around a dual-tracked crawler, which in itself represents a fully independent vehicle. A new three-dimensional multi-body dynamic simulation model of the tracked vehicle is developed, integrating the moist terrain’s mechanical model. Simulations assess the vehicle’s trafficability and performance, revealing optimal slip ratios for maximum traction force. Additionally, a mathematical model evaluates the vehicle’s tractive trafficability based on slip ratio and primary design parameters. The study offers valuable insights and a practical simulation modeling approach for assessing trafficability, predicting locomotion, optimizing design, and controlling the motion of tracked vehicles across diverse moist terrain conditions. The focus is on the critical factors influencing the mobility of tracked vehicles, precisely the sinkage speed and its relationship with pressure. The study introduces a rubber-tracked vehicle, pressure, and moisture sensors to monitor pressure sinkage and moisture, evaluating cohesive soils (Bentonite/Diatom) in combination with sand and gravel mixtures. Findings reveal that higher moisture content in Bentonite correlates with increased track slippage and sinkage, contrasting with Diatom’s notable compaction and sinkage characteristics. This research enhances precision in terrain assessment, improves tracked vehicle design, and advances terrain mechanics comprehension for off-road exploration, offering valuable insights for vehicle design practices and exploration endeavors. Full article

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. Full article

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. Full article