Search Results (137)

Every year, a billion tires are discarded worldwide, with only a small percentage being recycled. This leads to significant environmental hazards, such as fire risks and improper disposal. Silty sand also presents technical challenges due to its poor shear strength, susceptibility to erosion, and low permeability. This study explores the incorporation of crumb rubber derived from waste tires into silty sand to enhance its mechanical properties. Crumb rubber particles of varying sizes (3–6 mm, 5–10 mm, and 10–20 mm) were mixed with silty sand at 0%, 3%, 6%, and 9% percentages, respectively. Triaxial compression tests of unconsolidated and consolidated undrained tests with cell pressures of 100, 300, and 500 kPa were conducted. The deviatoric stress, shear stress, and stiffness modulus were investigated. The results revealed that the addition of crumb rubber significantly increased the deviatoric and shear stresses, especially at particle sizes of 5–10 mm, with contents of 3%, 6%, and 9%. Additionally, the stiffness modulus was notably reduced in the mixture containing 6% crumb rubber tire. These findings suggest that incorporating crumb rubber tires into silty sand not only improves silty sand performance but also offers an environmentally sustainable approach to tire waste recycling, making it a viable strategy for silty sand stabilization in construction and geotechnical engineering performance. Full article

The modern road industry requires a more effective solution according to efficiency and minimizing environmental burden. This article discusses the use of recycled materials to modify bitumen binders within the concept of the circular economy. The main aim of this article was to create a new composite based on waste materials, including polymer waste and rubber crumb. The important element is the usage of locally available waste that has not been investigated previously as a material for asphalt modification. The prepared composition was preliminarily assessed according to chemical composition. Next, research dedicated to road application was conducted, including the following: determination of the resistance to hardening, aging under the influence of high temperature and air, as well as oxidation processes, assessment of penetration, and evaluation of the softening point. The conducted studies showed that the new composites with the addition of polymer waste and rubber crumb improve the thermal stability, elasticity, and resistance of bitumen to aging. Optimum concentrations of modifiers were determined that provide an increase in the performance characteristics of bitumen, including a decrease in the brittleness temperature and an increase in the softening temperature. The obtained results demonstrate the potential for the introduction of new composites based on recycled materials in road construction, contributing to increased environmental sustainability and economic efficiency. Full article

The production of ordinary Portland cement has had a significant environmental impact, leading to increased interest in sustainable alternatives. This comprehensive review thus explores the performance and applications of rubberized alkali-activated concrete (RuAAC), an innovative material combining alkali-activated concrete with crumb rubber (CR) from waste tires as a coarse/fine aggregate replacement. The study examined current research on the components, physical and mechanical properties, and seismic performance of RuAAC structures. Key findings revealed that CR addition enhances dynamic characteristics while reducing compressive strength by up to 63% at 50% CR replacement, though ductility improvements partially offset this reduction. Novel CR pretreatment methods, such as eggshell catalyzation, can enhance seismic resilience potential. While studies on the structural seismic performance of RuAAC are limited, relevant research on rubberized conventional concrete indicated several potential benefits, highlighting a critical gap in the current body of knowledge. Research on the behavior of RuAAC in full-scale structural elements and under seismic loading conditions remains notably lacking. By examining existing research and identifying crucial research gaps, this review provides a foundation for future investigations into the structural behavior and seismic response of RuAAC, potentially paving the way for its practical implementation in earthquake-resistant and sustainable construction. Full article

International waste policy promotes the reduction and re-use of waste materials, and in some cases, specifically calls for the use of recycled materials in pavements. In countries like Australia, most of the aircraft pavement network is constructed of flexible pavements. Consequently, understanding the opportunities for recycled materials in flexible aircraft pavements is paramount to increasing the technology uptake. This paper reviews opportunities for the incorporation of recycled materials in flexible airport pavement construction, specifically, their application to particle substitution in unbound and asphaltic layers, use in stabilization treatments, and use as a bitumen modifier. Additionally, environmental product declarations are reviewed to provide a range of typical environmental costs for each recycled material when considering material processing for incorporation into flexible pavements. These materials are compared to virgin material environmental costs to determine which recycled materials provide the highest environmental benefit potential. It was concluded that particle replacement in unbound layers with waste materials had a similar environmental cost to using virgin materials. However, the requirement to dispose of waste material to the landfill can be significantly reduced. For asphaltic layers, recycled asphalt pavement as an asphalt mixture replacement, fly ash as a hydrated lime replacement, and waste plastic and crumbed rubber as a virgin polymer replacement all are effective in reducing the environmental cost. To further increase the technology uptake, a risk-based approach for the implementation of waste materials in airport flexible pavements is recommended, which considers performance testing, the depth of the pavement layer, and the pavement functional area. Full article

Rubberized concrete is a more environmentally friendly material than natural concrete as it helps to reduce rubber disposal issues and has superior impact resistance. Geopolymer concrete, on the other hand, is an economical concrete with higher mechanical properties than nominal concrete that uses fly ash and slag, among other industrial solid wastes, to lower carbon footprints. Rubberized geopolymer concrete (RuGPC) combines the advantages of both concrete types, and a thorough grasp of its dynamic compressive characteristics is necessary for its use in components linked to impact resistance. Despite the advantages of RuGPC, predicting its mechanical characteristics is sometimes difficult because of variations in binder type and combination. This research investigated the combined effect of ground granulated blast furnace slag (GGBFS) and fly ash (FA) on the workability, compressive strength, and stress–strain characteristics of RuGPC with rubber at 0%, 10%, and 20% fine aggregate replacement. Thereafter, energy absorption and ductile characteristics were evaluated through the concrete toughness and ductility index. Numerical models were proposed for the cube compressive strength, modulus of elasticity, and peak strain of RuGPC at different percentages of crumb rubber. It was found that RuGPC made with GGBFS/FA had similar stress–strain characteristics to FA- and MK-based RuGPC. At 20% of crumb rubber aggregate replacement, the workability, compressive strength, modulus of elasticity, and peak stress of RuGPC reduced by 8.33%, 34.67%, 43.42%, and 44.97%, while Poisson’s ratio, peak, and ultimate strain increased by 30.34%, 8.56%, and 55.84%, respectively. The concrete toughness and ductility index increased by 22.4% and 156.67%. The proposed model’s calculated results, with R² values of 0.9508, 0.9935, and 0.9762, show high consistency with the experimental data. RuGPC demonstrates high energy absorption capacity, making it a suitable construction material for structures requiring high-impact resistance. Full article

Due to the growing consumption of plastic and rubber products, effective waste management solutions are crucial. This study evaluates the use of crumb rubber (CR), low-density polyethylene (LDPE), and their combination (CR+LDPE), as asphalt binder modifiers for improving pavement performance and sustainability. The analyses covered two critical pavement layers: the wearing surface (WS) and the treated base (TB). The methodology included (1) Binder Development and Testing; (2) Superpave Mix Design; (3) mechanical testing, including Indirect Tensile Strength Testing and Semi-Circular Bending Testing; (4) life cycle cost analysis; and (5) carbon footprint analysis. The results revealed that CR+LDPE significantly enhanced the fatigue resistance of the TB mixes, with a fracture energy increase of 47%, and increased the flexibility index by 53% in the WS. CR increased the flexibility index by about 146% in the TB layer, while LDPE increased the fracture energy by 21% in the WS layer. The life cycle cost analysis demonstrated that using LDPE, CR, and CR+LDPE reduced the life cycle costs by about 16% in the WS layer. Meanwhile, the life cycle carbon footprint analysis showed that using LDPE and CR+LDPE reduced the carbon footprint by about 87% and 81% for the TB and WS layers, respectively. The study findings highlight the mechanical, economic, and environmental benefits of incorporating wastes into asphalt pavements. Full article

This study explores the potential of using sustainable materials in brick manufacturing by designing a novel brick mix in the laboratory, incorporating sand, lime kiln dust (LKD) waste, tyre rubber, and ground granulated blast furnace slag (GGBFS) waste. These cementless bricks blended LKD–GGBFS wastes as the binder agent and fine crumb rubber from waste tyres as a partial replacement for sand in measured increments of 0%, 5%, and 10% by volume of sand. Ordinary Portland cement (OPC) and fired clay bricks were sourced from the industry, and their properties were compared to those of the laboratory bricks. Tests performed on the industry and laboratory bricks included compressive strength (CS), freeze-thaw (F-T), and water absorption (WA) tests for comparison purposes. Additionally, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were performed on the bricks to assess the morphological and mineralogical changes responsible for the observed strengths and durability. The CS and WA values of the engineered bricks were 12, 6, and 4 MPa, and 7, 12, and 15%, respectively, for 0, 5, and 10% crumb rubber replacements. The industry bricks’ average CS and WA values were 13 MPa and 8%, respectively. From the results obtained, the green laboratory bricks passed the minimum strength requirements for load-bearing and non-load-bearing bricks, which can be used to construct small houses. Lastly, the engineered bricks demonstrated strength and durability properties comparable to those of the industry-standard bricks, indicating their potential as a sustainable alternative to help divert waste from landfills, reduce the pressure on natural fine sand extraction, and support eco-conscious brick production for a sustainable environment. Full article

Pavement systems in wet-freeze regions are prone to cracking, rutting, and moisture damage, making it challenging to incorporate recycled materials into asphalt mixtures in a way that enhances sustainability while maintaining performance and constructability. This study investigates and demonstrates the combined benefits of using processed waste glass in a leveling course and high-content crumb rubber in a surface course, focusing on both laboratory and full-scale field assessments in a wet-freeze region of northern Michigan. A leveling course containing 10% waste glass aggregate and a surface course using 16% crumb rubber (by binder weight) modified asphalt were designed with low air voids (3.0–3.5%) to promote thicker asphalt binder films for improved crack resistance. Laboratory results demonstrated that the combination of a 10% glass aggregate leveling course and a 16% rubber-modified surface course significantly enhanced low-temperature fracture energy while maintaining robust rut resistance and moisture durability. Full-scale construction in northern Michigan corroborated these findings; field cores from rubber and glass sections surpassed performance thresholds for rutting, cracking, and noise reduction. This study demonstrates that integrating crumb rubber and waste glass into asphalt pavements offers both environmental and performance benefits. The approach presents a scalable solution for enhancing pavement durability in wet-freeze regions. Full article

The article reports on the development of a fundamentally new, effective technology for recycling waste tires using the explosive-circulation technology method, which was implemented in industry at a working factory. The construction of an explosion-circulation reactor, in which tires are destroyed under the influence of an explosion, is described. The main technological stages of the reactor operation include the formation of a tire package with a height of about 2.4 m and a mass of up to 1000 kg; cooling the package by air turbo-cooling machine to a temperature of minus 70–80 °C; placing the package into the reactor; initiating the explosive charge; and removing the tire shedding products with a subsequent granulometric classification of the resulting rubber crumb. The resulting rubber crumb has good wettability, which eliminates the need for an additional technological stage of activating the crumb surface. This made it possible to successfully use the obtained rubber crumb to improve the characteristics of road construction bitumen, the hardness of which at −16 °C decreased from 217 to 161 MPa. Using atomic force microscopy (AFM), gas chromatography, mass spectrometry, GPC, and XPS, it was established that the good wettability of the crumbs is explained by the formation of molecules with polar groups (C-O, C=O, C(O)O, C-S, C-SO_x, Zn-S, O-Si(O)-O) on the crumb surface as a result of the explosion. Full article

The scarcity of natural aggregates and the growing accumulation of waste materials have driven the demand for sustainable and circular economy solutions in transportation infrastructure, and this has led to the utilization of waste materials in transport infrastructure, such as recycled rubber. Although numerous laboratory experiments have been conducted on granular mixtures mixed with rubber, predicting the complex stress–strain behaviour of these mixtures mathematically and capturing the influence of rubber on the geotechnical properties of waste mixtures are imperative. This paper presents a comprehensive review of the constitutive models developed to predict the stress–strain behaviour, dilatancy, and shear strength of rubber-mixed waste materials, including sand–rubber, coal wash–steel furnace slag–rubber crumbs, and coal wash–rubber crumbs in various transport infrastructure applications under static loading. This paper also highlights the innovations and limitations of these existing constitutive models on rubber-mixed materials. It was found that existing constitutive models based on hyperbolic, hypoplastic, critical state, and bounding surface plasticity approaches can capture the behaviour of these materials under static loading conditions. However, further developments are required to incorporate the influence of the type and size of the rubber, particle breakage, and damping properties and also account for train-induced cyclic loading in models developed for railway substructures. This paper contributes to advancing future research aimed at deepening the fundamental understanding of rubber-mixed materials used in transportation infrastructure. Full article

This study explores the innovative use of recovered tire-derived aggregates in cement-based mortars to enhance thermal insulation and reduce environmental impact. The research addresses the pressing global challenge of managing end-of-life tires (ELTs), which are non-biodegradable and contribute significantly to waste management issues. By incorporating crumb rubber from recycled tires into mortars, this study investigates the feasibility of creating lightweight, thermally insulating mortars suitable for building repair and rehabilitation. The primary objective is to develop mortars that minimize structural load, decrease energy consumption in buildings, and promote the recycling of ELTs as a valuable resource. The study focuses on evaluating how varying crumb rubber content affects key properties such as workability, thermal conductivity, compressive strength, and fracture energy. Experimental tests were conducted to assess these properties, with the results indicating that mortars with up to 50% crumb rubber content exhibit improved thermal insulation and meet industry standards for non-structural repair applications. The methodology involved creating eight different mortar mixtures with varying proportions of crumb rubber particles (ranging from 0% to 100%). Each mixture was tested for physical and mechanical properties, including density, workability, air content, setting time, thermal conductivity, and strength. The experimental results showed that as the crumb rubber content increased, the thermal conductivity of the mortars decreased, indicating enhanced insulation properties. However, higher crumb rubber content led to reduced mechanical strength, highlighting the need for a balanced approach in material design. Key findings reveal that the air content of early-age mortar paste increases linearly with the crumb rubber replacement ratio, impacting the hardened behavior by concentrating stresses or facilitating the infiltration of damaging elements. The study also establishes relationships between mortar properties and crumb rubber content, contributing to the development of sustainable construction materials. The environmental benefits of recycling ELTs are emphasized, as this practice reduces the reliance on natural sand, a resource that is the second most consumed globally after water. This study underscores the viability of using crumb rubber from recycled tires in mortars for repair and rehabilitation purposes. The developed mortars, particularly those with 25% to 50% crumb rubber content, show promise as non-structural repair products, offering improved thermal insulation and reduced environmental impact. Full article

Railway track performance and durability face growing challenges from higher speeds, heavier axle loads, and changing environmental conditions. Crumb rubber-modified asphalt (CRMA) offers a sustainable solution by repurposing waste tires into a durable material for railway trackbeds, improving both performance and environmental impact. Following PRISMA-ScR guidelines, this scoping review synthesizes an extensive body of global research on the structural, mechanical, and environmental benefits of CRMA in railway trackbeds. A systematic literature search was conducted across major academic databases, covering studies published over several decades. Selection criteria focused on CRMA applications in railway trackbeds, using keywords such as “crumb rubber-modified asphalt”, “railway track vibration”, and “sustainable railway materials.” After rigorous screening and eligibility assessment, the most relevant peer-reviewed studies were included, emphasizing mechanical performance, durability, and environmental impact. Key findings indicate that CRMA effectively reduces ground vibrations, enhances load distribution, and lowers long-term maintenance costs while promoting sustainable waste management through tire recycling. However, challenges such as optimal mix design, potential emissions, and long-term bonding stability require further investigation. Additionally, the review was limited to English-language studies, potentially omitting relevant non-English research, and some reports were inaccessible during retrieval. This review maps critical research gaps, identifies key areas for future optimization, and highlights CRMA’s potential to advance resilient and eco-friendly railway infrastructure. Full article

Disposing of waste tyres in landfills poses significant environmental hazards, making recycling a crucial alternative. Rubberised concrete has been found to exhibit lower density and better thermal insulation performance than conventional concrete. In order to maximise the potential of thermal insulation of rubberised concrete, this study investigates the mechanical and thermal properties of foamed rubberised polypropylene fibre concrete (FRPFC). FRPFC was produced using a mix of crumb rubber (CR) granules, polypropylene fibres, and foam, targeting a density of 800 kg/m³, with CR substituting sand at varying levels. Compressive strength, flexural strength, splitting tensile strength, and thermal conductivity of FRPFC were evaluated. The results demonstrate that increasing CR granule content enhances compressive strength due to reduced porosity from lower foam usage. For instance, compressive strength improved by 55% (2.64 to 4.10 MPa) as CR granule content increased from 0% to 80%. Similarly, flexural strength and splitting tensile strength increased by 55% (1.61 MPa to 2.49 MPa) and 39% (0.41 MPa to 0.57 MPa), respectively, when CR content rose from 0% to 100% at a water-to-cement ratio of 0.50. Furthermore, thermal conductivity decreased by 34% (0.3608 W/mK to 0.2376 W/mK) when sand was fully replaced with CR granules, showcasing improved thermal insulation. Statistical analysis using ANOVA confirmed that the crumb rubber content significantly influences the mechanical and thermal properties of FRPFC, with higher CR content (80% and 100%) leading to superior performance. These findings highlight FRPFC’s potential as an environmentally sustainable and thermally efficient construction material, contributing to enhanced mechanical properties compared to conventional foamed polypropylene fibre concrete. Full article

Concrete, having evolved over the last 2000 years, is integral to modern infrastructure, with continuous innovations aiming to address sustainability challenges. From Roman concrete mixes to the invention of Portland cement (PC), concrete has evolved to meet growing infrastructure demands. As urbanization and energy consumption increase, the construction industry is focusing on high-performance materials, recycling, and minimizing harmful substances. Research on sustainable concrete alternatives shows promising reductions in global warming potential and other environmental impacts compared to traditional PC. However, challenges such as higher material costs and performance limitations remain. Alternatives such as alkali-activated concrete (AAC), self-healing concrete, and bacterial concrete (BC) have emerged in response to environmental concerns, along with fiber-reinforced AAC, waste-based concrete composites, and the reuse of construction and demolition waste (CDW), further enhancing sustainability. Foamed concrete, with its lightweight and insulating properties, offers additional potential for reducing environmental impact due to its ability to incorporate recycled materials and reduce raw material consumption. Technologies like three-dimensional concrete printing (3DCP) are improving resource efficiency and reducing carbon footprints while also lowering labor and material waste. However, concerns regarding cost-effectiveness and social sustainability persist. Overall, continued innovation is the key to balancing performance, cost, and sustainability in the development of concrete and to meet the growing demands of global infrastructure. Full article

Asphalt modified with treated waste tires has good environmental protection and application value. However, the nano-interaction mechanism of crumb rubber (CR) and asphalt (especially its components) is unclear. In this study, molecular models of asphalt, asphalt components, CR, and CR-modified asphalt (CRMA) were constructed by molecular dynamics (MD) simulation. The validity of the model construction and parameter setting was verified by multiple indexes. The influence mechanism of CRMA density, asphalt-CR compatibility, mechanical indexes, and binding energy under the influence of temperature, CR dosage, and other factors was systematically analyzed. Results showed that the optimum temperature for preparing and storing to prevent segregation did not coincide. The solubility parameters (S_P) prediction model of the asphalt’s four components was obtained based on the multiple linear regression method. CR could enhance the mechanical properties of asphalt, but the improvement was limited to small dosages. Increasing the dosage can enhance the mechanical properties of asphalt; the mechanical properties can be significantly improved in medium- and high-temperature conditions. Bulk modulus and shear modulus were recommended for preferential analysis of the mechanical properties of CRMA. It is recommended that the optimal dosage be 20%. Full article