Search Results (99)

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

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

The use of recycled rubber particles, in the form of crumb rubber (CR), in concrete is gaining momentum due to its environmental benefits and potential for enhancing ductility. However, the strength degradation associated with CR incorporation remains a concern. This study investigates the compressive and axial behavior of reinforced concrete columns incorporating CR and hybrid steel fibers, comprising recycled steel fibers (RSFs) and copper-coated micro steel fibers (MSFs). Sixteen circular columns with varying CR contents (0–20%) and a constant fiber dosage (0.7% RSF and 0.3% MSF by volume) were cast and tested under axial compression. The results showed that CR reduced compressive strength, while the addition of hybrid fibers significantly improved strength, ductility, and energy absorption. Columns with up to 8% CR and fibers demonstrated comparable or superior load-bearing capacity to conventional concrete. Finite element modeling using ABAQUS software (Version 6.9) validated the experimental results, with numerical predictions closely matching load–displacement behavior and failure modes. This study highlights the potential of using CR and hybrid steel fibers in structural concrete to promote sustainability without compromising performance. Full article

Crumb rubber (CR) obtained from end-of-life tyres (ELT) has gained significant attention in the sustainable design of asphalt pavements in recent years, showing a promising perspective in the enhancement of pavement performance related to its structural and functional properties. Existing research on CR influence on pavement performance mostly focused on peculiarities of asphalt mixture modification procedures—dry and wet processes, CR content in the mixture and CR particle size. In this study, a laboratory-based experimental investigation of CR effect on two different mixture gradations, namely dense-graded and gap-graded mixtures with three different binder contents, was performed. CR was added in mixtures through binder modification, with a constant CR content of 18% by binder weight in all mixtures. Volumetric properties—maximum mixture density, bulk density and void characteristics, alongside mechanical properties determined by the Marshall test method—were determined on unmodified and modified mixtures. The goal was to evaluate the influence of CR modification with respect to three different binder contents. The results showed that gap-graded mixtures are more sensitive to change in CR modified binder content in comparison to dense-graded mixtures in terms of air voids content. Furthermore, the mechanical properties of CR-modified mixtures were slightly enhanced in gap-graded mixtures, showing a promising potential of CR modification for pavement performance. However, the choice of optimal binder content in CR-modified mixtures was shown to be a critical mixture design parameter due to the increased sensitivity of binder content change to the analysed voids properties and permanent deformations. 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

A numerical analysis of rubberized reinforced concrete columns’ performance under cyclic loading is presented in this study. Three different concrete blends (M1, M2, and M3) were chosen based on the volume of fine aggregate replaced by varying percentages of crumb rubber (CR) (0%, 10%, and 15%). Under cyclic loads, three groups of rubberized reinforced concrete (RRC) columns with circular, square, and rectangular cross-sections and heights of 1.5 m and 2.0 m were analyzed using the finite element software ABAQUS. The proposed model effectively predicts the behavior of rubberized reinforced concrete columns under cyclic loading. Additionally, these columns demonstrate improved performance in lateral displacement, displacement ductility, and damping ratio, with only a slight reduction in lateral load capacity. For the circular columns with a height of 1.5 m, the displacement ductility increased by 47.8% and 89.0% when the fine aggregates were replaced with 10% and 15% CR, respectively. Similarly, for square columns of the same height, the displacement ductility increased by 18.7% and 26.7% with 10% and 15% CR, respectively. The rectangular specimens exhibited enhancements of 34.74% and 58.95%, respectively. Although the analyzed rubberized reinforced concrete columns experienced slight reductions in the lateral load capacity compared to the non-CR columns, the cyclic damage resistance was notably improved. Full article

Rubber materials enter aquatic environments by stormwater runoff via sources such as playground mulch, athletic fields, and roadway surfaces. Tire rubbers are considered plastics as they comprise a substantial portion of synthetic polymers. Rubber particles are complex and variable depending on the type, source, and age of rubber. In this study, zebrafish embryos and daphnids were exposed to nano-scale or micro-scale particles, or leachate from recycled rubber (RR), crumb rubber (CR), and cryo-milled tire tread (CMTT). Zebrafish embryos were evaluated for lethal and sub-lethal effects over a 120 h exposure, while daphnids were tested over a 48 h period. Nano-scale RR, CR, and CMTT particles elicited a hatch delay in zebrafish embryos with similar EC₅₀ values (1.3 × 10⁹–1.4 × 10⁹ particles/mL). Micro-scale particles did not elicit any significant effects in developing zebrafish. Nano-scale particles of all rubber materials significantly increased hatch delay compared to leachate, suggesting an adverse nanoparticle effect unexplained by chemical leaching alone, indicating tire particle-specific effects. Daphnia RR micro- and nanoparticle exposures resulted in mortality, with LC₅₀ values of 9.8 × 10⁵ microparticles/mL and 5.0 × 10⁸ nanoparticles/mL, respectively. Leachate exposures did not elicit significant Daphnia mortality. Sublethal micro- and nano-TP exposures significantly decreased microalgae ingestion by Daphnia after 24 h. The effects of tire-derived exposures observed pose a risk to aquatic organism survival at environmentally relevant concentrations. 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

Asphalt modified with treated waste tires has good environmental protection and application value. However, the nano-modification mechanism of crumb rubber (CR) with asphalt is still unclear. This research investigates the mechanism, aging, and interfacial interaction with the aggregate of CR modification asphalt (CRMA). The base asphalt and CRMA (original and aged) and two typical aggregate models were constructed. The accuracy of the model was verified through multiple indicators. The effects of CR and aging on the physical properties (density, compatibility, and diffusion coefficient), mechanical properties, component interaction behavior, and interfacial interactions with aggregates of CRMA were systematically analyzed. The results showed that the CR reduced the diffusion coefficient of asphalt by about 31%. The CR inhibited the movement of the components of asphalt (especially saturate and aromatic), which significantly improved the mechanical properties of asphalt. The compatibility between asphalt and CR significantly deteriorated after aging. The difference in the solubility parameter was about four times that before aging. It is instructive for the regeneration of CRMA. Aging led to a decrease in the shear modulus and Young’s modulus of both base asphalt and CRMA, which verified and quantified the adverse effects of aging on the mechanical properties. Comparing the two aggregates, CaCO₃ had a greater adhesion with asphalt than SiO₂. The difference ranged from 22.5% to 39.9%, which quantified the difference in the adhesion properties of acid base aggregates with asphalt. This study can provide theoretical guidance for the modification and application of CRMA. Full article

The global rise in vehicle ownership has led to a significant accumulation of waste tires, with many ending up in landfills or incinerated, resulting in considerable environmental impacts. Several end-of-life solutions have been developed to repurpose these tires, and one promising approach is converting them into crumb rubber for use in road infrastructure. Crumb rubber has been incorporated as a stabilizing agent in asphalt mixtures, Portland cement concrete, base and sub-base granular layers, and subgrades. This application not only mitigates environmental harm but also often enhances the mechanical performance of these materials. Additionally, crumb rubber (CR) serves as a low-carbon material, offering environmental benefits such as reduced carbon footprint. This study provides a comprehensive literature review on the use of crumb rubber in road infrastructure materials, examining aspects such as treatment methods, mix design, mechanical properties, durability, and environmental impacts. It also highlights knowledge gaps and potential research directions to advance the application of crumb rubber in the road infrastructure industry. The findings suggest that, at appropriate dosages (in asphalt mixtures, for example, it is between 15–20% by weight of asphalt binder), crumb rubber can shift from being an environmental burden to a valuable resource across numerous road infrastructure applications. This review aims to guide agencies, designers, engineers, and other stakeholders in informed decision-making. Full article

This research explores the thermal and mechanical properties enhancement in hollow concrete blocks by incorporating recycled expanded polystyrene (EPS) and crumb rubber (CR). Key thermal properties—including average thermal resistance ($\overline{R}$), average thermal conductivity ($\overline{\lambda }$), and average specific heat ($\overline{Cp}$)—were analyzed, while mechanical properties were evaluated via compressive strength tests. Findings indicate that the addition of EPS and CR significantly improved thermal resistance, with specific heat and compressive strength remaining within acceptable thresholds. The optimal mixture of 35% EPS and 5% rubber by volume led to a remarkable 49.67% increase in thermal resistance compared to standard hollow blocks while still achieving a compressive strength ($\overline{\sigma }$) around 7 MPa. These results classify the blocks as non-load-bearing, highlighting their potential for energy-efficient construction using sustainable materials. This research advances sustainable building materials by providing practical solutions to improve building performance in Lebanon. Full article

Researchers are increasingly concerned about the vast amounts of waste rubber tires produced globally, which contribute significantly to environmental pollution. The potential of incorporating waste rubber tires to modify bitumen has garnered considerable interest. This study assesses pavement design temperatures according to SUPERPAVE standards for representative Malaysian regions. The assessment is based on hourly air temperature data and simulates temperature diffusion in typical Malaysian road pavements using the finite difference method (FDM). Tests on neat bitumen (PEN 60/70) and crumb rubber-modified bitumen (CR-TMB) samples evaluated their physical and rheological properties across various temperatures and aging stages. These tests were conducted using the dynamic shear rheometer, rotational viscometer, and bending beam rheometer. The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis provided insights into the aging processes of both PEN 60/70 and CR-TMB. The findings indicate that adding 15% crumb rubber to produce CR-TMB enhances the physical and rheological properties of bitumen. Additionally, this modification significantly improves aging behavior, highlighting its potential for more resilient and sustainable road construction materials. Therefore, the use of crumb rubber in road construction should be considered to improve pavement durability and strength. Furthermore, utilizing crumb rubber as an alternative material can reduce costs by recycling waste materials. Full article

This study focuses on exploring tensile properties and nanoscale phase structures of different modified asphalts, and their aging behavior. For this, one virgin asphalt and three modified asphalts, namely, 4% SBS-modified asphalt, 2% SBS and 20% crumb rubber (CR) composite asphalt, and 4% SBS and 2%TiO₂ composite asphalt, were prepared and investigated using the force-ductility test and atomic force microscopy (AFM). Also, detailed experiments of short-term (STA) and long-term (LTA) aging were conducted to obtain aged asphalt specimens. The results showed that a ductile fracture was found for the three modified asphalts. However, for the activation energy, SBS asphalt and SBS&TiO₂ asphalt were 2.87 times and 3.31 times that of SBS&CR asphalt, respectively. This demonstrates that the activation of the SBS polymer phase requires more energy during the stretching process when the rubber powder is not present. SBS&CR asphalt and SBS&TiO₂ asphalt showed better tensile properties and aging resistance in terms of the quantitative results of tensile property indicators, indicated by a larger value of fracture ductility, tensile compliance, and the toughness ratio under the same aging condition. According to the AFM results, SBS modifier had little effect on the phase structure of virgin asphalt, while TiO₂ modifier increased the number of bee phases and made their distribution more uniform, indicating the formation of a more stable phase structure system. This may contribute to its better tensile properties and aging resistance. Moreover, TiO₂ molecules inhibited the aggregation behavior of polar molecules during the aging process, which led to a reduction in surface roughness. By comparison, the effect of aging on the phase structure of SBS&CR asphalt was more significant among the three modified asphalts. This result can be attributed to the interaction between rubber powder particles and asphalt. Full article

The issue of forming a reliable and sustainable structure of crumb-rubber-modified binder is an important scientific and technical task. The quality of this task will increase the technical and economic efficiencies of road construction materials. This work is dedicated to developing a scientifically justified method of directed thermomechanical devulcanization, which ensures the solubility of the crumb rubber in the complex structure of a polydisperse composite material, preventing the formation of aggregates consisting of unsaturated crumb rubber particles, whose elastic aftereffect causes intensive cracking, especially during low-temperature road operations. The novelty in the first part of this article is due to the fact that, for the first time, the quantitative ratio of the polymer component in the crumb rubber was experimentally determined. The ratio of the polymer component to the total content of the other rubber components in the crumb rubber (CR) was determined to be, on average, 93.3 ± 1.8%. The stabilities of the compositions of crumb rubber from different batches were experimentally studied. The nature of the polymer component in the crumb rubber was determined. A hypothesis was formulated to obtain a thermodynamically stable and sustainable binder modified with crumb rubber. To evaluate the compatibility of hydrocarbon plasticizers with the studied CR samples, the following semi-empirical and thermodynamic compatibility parameters were calculated: Hildebrand solubility parameters based on evaporation energy and surface tension, Barstein’s compatibility parameter |X|, Traxler coefficient, and the mass ratio of paraffin naphthene:asphaltenes. It was shown that for the substances under study, it is advisable to justify the choice of plasticizer based on chemical compatibility criteria. It was established that a supramolecular plasticization mechanism occurs in the “hydrocarbon plasticizer–crumb rubber” systems under consideration. In the development of the crumb-rubber-modified binder, it was found that the use of activated crumb rubber (ACR) from large tires does not ensure the achievement of a stable and resilient structure of the crumb-rubber-modified bitumen. Full article

The crumb rubber (CR) asphalt has some defects of high viscosity and poor storage stability, which brings great challenge to the high-quality construction of the CR asphalt pavement. To improve the interaction between the CR and base binder, the Eucommia ulmoides gum (EUG) with double-bond structure similar to trans-polyoctenamer rubber (TOR) was used to modify the CR asphalt. However, the original EUG double bond is basically inactive at room temperature and cannot form the effect of TOR. Open double bonds of EUG with asphalt and rubber powder form a network structure similar to TOR-modified rubber asphalt by high-temperature mixing with EUG in a torque rheometer. The effects of modified CR on rubber asphalt were analyzed by macro- and micro-experiments such as rotational viscosity tests, segregation tests, FTIR tests, and PG tests. It was found that the high-temperature mixing process works in both physical and chemical ways to mix the CR and EUG into an inseparable substance. The modified CR has higher chemical activity after desulfurization and degradation, which allows it to form a more effective chemical connection with asphalt. EUG can build a stable spatial crosslinking structure in CR asphalt due to the sulfurization reaction, which significantly improves the construction workability and system stability of the CR asphalt. Full article