Recycled Crumb Rubber Research Articles

Incorporating Recycled Crumb Rubber into Asphalt: A Comprehensive Review

Incorporating Recycled Crumb Rubber into Asphalt: A Comprehensive Review

3D Cementitious composites printing with pretreated recycled crumb rubber: mechanical and acoustic insulation properties

ABSTRACT Cementitious materials incorporating recycled crumb rubber have become a common sustainable resolution in diverse building environments to achieve various functions in terms of lightweight, ductility, as well as energy absorption. This study explored the 3D printed rubberised cementitious composites (3DPRC) in two aspects: examining the effects of crumb rubber pretreatment conditions on compressive properties; conducting experimental and numerical analysis on the acoustic dissipation characteristics of 3DPRC. Fine crumb rubber granules (3-5 mm) replaced 10%, 20%, and 30% of river sand in the composites. Uniaxial compression tests indicated that the compressive strength of 3DPRC decreased with the increase of crumb rubber content and introduced anisotropic behaviour. Impedance tube tests were conducted to evaluate the sound absorption and insulation capabilities of 3DPRC. An optimal Noise Reduction Coefficient (NRC) of 0.35 was achieved with 30% crumb rubber. The sound insulation properties depend strongly on the mass density and porosity of the 3DPRC. Additionally, it is proved that the volume of built-in air gap has positive effects on both sound absorption and insulation properties. The results from Finite Element Method (FEM) numerical simulations correlated well with experimental data, proving the efficiency of the simulation and validating the experimental results.

Dynamic responses of rubberised concrete: A study using short-length F-shape barriers subjected to pendulum impact

This study evaluates rubberised concrete barriers' dynamic responses and failure mechanisms subjected to pendulum impacts. We constructed short-length F-shaped barriers from concrete mixed with varying proportions of steel fibres (0 %, 1 % and 2 %) and recycled crumb rubber (0 %, 30 % and 60 %). These barriers were then tested under controlled pendulum impacts, where we measured their peak impact forces, displacements, and energy absorption capacities at different impact velocities. Our findings reveal that barriers with rubber displayed significantly higher energy absorption and lower peak impact forces at low velocities than standard concrete barriers. Conversely, incorporating steel fibres into rubberised concrete increased the peak impact forces and reduced displacements, indicating enhanced stiffness. The experimental data facilitated the development of a predictive equation for peak impact forces, accounting for impact velocity and material composition. This research demonstrates rubberised concrete's less hazardous failure modes and enhanced impact resistance and energy absorption capabilities when used in roadside barriers. Our findings offer valuable insights for developing safer, more resilient infrastructure and contributing to environmental sustainability by repurposing waste materials.

Experimental and Numerical Evaluation for Hybrid Reinforced T-Beam with Different Ratios of Recycled Rubberized Concrete

The use of hybrid GFRP and steel bars as main reinforcement increases the flexural capacity of T-section concrete beams and reduces ductility. Adding recycled rubber to the concrete mix would further enhance the ductility of the hybrid system. Evaluation of the concrete's flexural capacity and ductility is the main goal of the current investigation using normal concrete (NC) and rubberized recycled concrete (RRC). Eight T-beams have been experimentally investigated in this research, two beams were reinforced with steel bars and GFRP bars with zero percentage of crumb rubber (C.R). The remaining beams were reinforced with different combinations of GFRP and steel bars with rubberized concrete mixes with partial substitution of sand with recycled crumb rubber by (0%, 7.5%, 10%, and 12.5% replacements by volume) particle size 1.0 to 2.0 mm. The ductility index for the tested hybrid rubberized T-beams (HRTB) BRH1, BRH3a, BRH5, BRH2, BRH4, and BRH6, were higher than BH1 and BH2 by 28.2%, 35.47%, 65.38%, 23.76%, 30.04%, and 56.95% indicating that increasing the percentage of C.R. has a direct effect on increasing the ductility index. The ultimate failure load for the tested HRTB BRH1, BRH3a, and BRH5, decreased by 11.68%, 14.29%, and 17.47% compared to the hybrid T-beam BH1. The energy dissipation decreased for HRTB BRH1, BRH3a, BRH5, BRH2, BRH4 and BRH6 by 7.88%, 12.36%, 17.17%, 8.12%, 12.96%, and 18.28 compared to hybrid T-beams BH1 and BH2. This indicates that the existence of the very weak C.R. was not able to dissipate the energy properly within the concrete matrix. Good agreement was found between the numerical model and experimental results in terms of crack pattern, ultimate loads and deflections.

Durability and Recycling of Rubber Concrete

The addition of crumb rubber particles causes a decrease in the compressive strength of concrete. This is particularly observed beyond 3.6% crumb rubber addition with respect to the total weight of the aggregates. The accelerated carbonation also indicates an increase in the CO2 ingress, which is partially due to the low quality of the interface rubber particles-cementitious matrix. On the other hand, the water sealant properties, the chloride penetration resistance and the resistance to freeze and thaw exhibit an increase. This latter feature is mainly due to the implemented ductility of the crumb rubber concrete, which can better adapt to the thermal stress that arises during the freezing action. Furthermore, the addition of recycled crumb rubber up to 25% of the aggregate weight to concrete positively affect the mechanical as well as the durability performance.

Effect of the reclaiming degree of catalytic pre-desulfurization recycled crumb rubber on the properties of modified asphalt

The application of crumb rubber (CR) as an asphalt modifier in flexible pavements is an effective way to achieve sustainable utilisation. The performance of crumb rubber modified asphalt (CRMA) can be improved by pretreatment of CR to make it desulfurized to a certain extent. This study aims to determine the optimal regeneration degree of CR to obtain CRMA with better performance. Recycled crumb rubber (RCR) was prepared by catalytic regeneration at low temperatures and used to prepare recycled crumb rubber-modified asphalt (RCRMA). Furthermore, the characteristics of RCR with different regeneration degree and the performance of RCRMA were investigated to determine the reasonable range of regeneration degree. The results showed that solubility was a reliable indicator of the degree of regeneration of RCR and that the solubility of RCR was positively correlated with its regeneration degree. The higher the degree of RCR regeneration, the lower the molecular weight, the more uniform the distribution, and the larger the surface structure. The low-temperature performance, fatigue resistance, and construction workability of the RCRMA were better than those of the CRMA. When the solubility of RCR was greater than 30%, the compatibility and storage stability of RCRMA were significantly improved. As the solubility of RCR increases, the high-temperature performance of RCRMA decreases; however, as long as the solubility of RCR does not exceed 60%, the decrease in the high-temperature performance of RCRMA is very small. According to a comprehensive analysis, the solubility of RCR should be maintained at 30–60%.

Ultra-High-Performance Alkali-Activated Concrete: Effect of Waste Crumb Rubber Aggregate Proportions on Tensile and Flexural Properties

The declining availability of natural sand resources and the significant carbon footprint associated with the extensive use of cement are posing severe limitations on the advancement and application of ultra-high-performance concrete (UHPC). In this study, waste tyre-derived recycled crumb rubber particles (CR) were employed to replace quartz sand, and an alkali-activated cementitious material was used to produce waste tyre-alkali-activated UHPC (T-UHPAC). The influence of different CR replacement ratios (0%, 5%, 20%, 35%, 50%) on the tensile and flexural performance of T-UHPAC was investigated, and a predictive model for the stress–strain response considering the CR replacement ratio was established. An optimization method for improving the tensile and flexural performance of T-UHPAC was proposed. The results indicate that the effect of rough-surfaced CR on the interfacial properties of concrete differs from that of smooth quartz sand. A CR replacement ratio exceeding 35% led to a reduction in both the tensile and flexural strengths of UHPAC, while a replacement ratio at or below 20% resulted in a superior tensile and flexural performance of T-UHPAC. The established predictive model for tensile performance accurately forecasts the stress–strain behaviour of T-UHPAC under varying CR replacement ratios, with the accuracy improving as the CR replacement ratio increases. By utilizing CR to replace quartz sand in proportions not exceeding 20%, the production of low-carbon UHPC with exceptional comprehensive mechanical properties is achievable. Moreover, the development of T-UHPAC through the comprehensive utilization of waste tyres presents a promising and innovative approach for the low-carbon and cost-effective production of UHPC, thereby facilitating the sustainable development of natural resources. This research represents a significant step towards the widespread adoption and application of UHPC and thus holds substantial importance.

Cracking resistance of crumb rubber modified green asphalt mixtures, using calcium carbonate nanoparticles and two by-product wax-based warm mix additives

Common procedures to incorporate the recycled crumb rubber (CR) in asphalt binders take a long time and use a high-temperature heating process, which makes these rubberized mixtures even more expensive and environment-unfriendly than conventional mixtures. In trying to make a cheaper and greener asphalt mixture, in this paper, the CR incorporation heating process and its duration were lowered (140–150°C in 15 minutes), and the effect of these changes was studied on the pavement's tensile/shear cracking resistance. Because the main disadvantage of using CR is the increase of viscosity, two by-products, slack wax (SW) and polypropylene wax (PPW) were used to correct the viscosity; also their effect on fracture toughness (Keff) and fracture energy (Gf) was assessed. As results showed that the following process decreases the cracking resistance, calcium carbonate nanoparticles (CCN) in different contents were added. Results show that adding 15% CR reduces Keff and Gf by about 18 and 16%, respectively. Adding the SW and PPW further reduces them by about 8 and 16%, respectively. In this condition, adding CCN in optimal content (about 5%) compensates for these reductions. Although these greener asphalts have the same cracking resistance as the control mixture, the environmental and cost-effectiveness analysis shows the developed materials are greener and cheaper.

Development of dynamic shear-rheology-based method to improve evaluation of swelling degree of recycled crumb rubber in asphalt rubber

Inappropriate disposal of substantial scrap tires has become an unavoidable and imminent environmental concern. Asphalt rubber (AR) facilitates the value-added recycling of scrap tires into eco-friendly and durable pavement, showcasing immense potential for pollution alleviation and resource conservation. In preparing AR, the swelling effect of rubber plays a dominant role in the gel-like network formation and performance enhancement of the modified asphalt. Accordingly, it is crucial to accurately evaluate the rubber swelling degree for guiding AR preparation and mixture design. Existing research mainly relies on measuring the volume of expanded rubber particles to assess the rubber swelling degree, which requires sophisticated instruments or a cumbersome process of extracting the crumb rubber. In this study, a method was proposed to conveniently evaluate the swelling degree of crumb rubber based on the dynamic shear rheological indicators. Firstly, the base asphalt was mixed with crumb rubber at different levels of time to prepare AR binders with varying swelling degrees. The mechanical properties (i.e., elastic recovery) and physical properties (i.e., volume expansion) were measured and analyzed to investigate the impacts of swelling time on AR properties. Secondly, the rheological properties of AR with different swelling degrees were measured via temperature sweep (TS) test, multiple stress creep recovery (MSCR) test, and linear amplitude sweep (LAS) test. Thirdly, the particle effect (PE) and interaction effect (IE) values were calculated, and the swelling degrees were determined based on the variations of PE values. Relationships between swelling degrees and PE-related indicators were established to facilitate the development of the new evaluation method. Finally, the swelling degrees evaluated by the newly developed method were compared with volume expansion to validate its reliability. The results from different rheology tests were also used to verify the feasibility of the proposed method, and the prediction of swelling degree against the swelling time was established. The findings of this research provide references for evaluating the swelling degree of crumb rubber conveniently and accurately.

Study on the Physical and Rheological Characterisation of Low-Density Polyethylene (LDPE)/Recycled Crumb Rubber (RCR) on Asphalt Binders

Recycled crumb rubber (RCR) is considered a reliable asphalt modifier and a solution to the problem of scrap tyre recycling. RCR-modified asphalt (RCRMA) typically has good low-temperature performance and storage stability. However, the pre-treatment of crumb rubber (CR) impairs its physical properties, resulting in poor high-temperature performance, which limits the industrial application of RCRMA. In this study, low-density polyethylene (LDPE) composite RCR was used to modify asphalt, and LDPE/RCR-composite-modified asphalt (L-RCRMA) was produced to compensate for the deficiencies in the high-temperature performance of RCRMA. The comprehensive physical properties of L-RCRMA were elucidated using tests such as the conventional properties, rotational viscosity, and rheological tests. The results showed that the incorporation of LDPE improved the high-temperature stability and rutting resistance of the asphalt, but an excessive amount of LDPE impaired the low-temperature performance and storage stability of L-RCRMA. Therefore, it is necessary to control the amount of LDPE to balance the performance of the asphalt. On this basis, we recommend a dosage of 20% for RCR and 1.5% for LDPE.

Influence of filler concentration and type on rheological and mechanical properties of liquid isoprene rubber for high-strength parts via material extrusion

This study investigates the rheological behavior and material extrusion performance of liquid isoprene rubber (LIR) compounds filled with carbon black (CB), silica (Si), and recycled crumb rubber (CR) fillers for potential additive manufacturing applications. The rheological properties of the LIR mixtures were characterized using flow curve analysis and temperature sweeps, identifying shear-thinning behavior and temperature-dependent viscosity ultimately reflecting the final dimensional tolerance of the prints. Vulcanization time (t90) was determined using oscillatory rheometry, and the effect of filler concentration on t90 was evaluated. Mechanical testing was conducted to assess the hardness and tensile properties. The results demonstrate the influence of filler concentration on the rheological properties, printability, and mechanical performance of the LIR compounds thus resulting in the printing of high-strength (σu > 5 MPa) isoprene rubber parts capable of being additively manufactured.

Performance of Geogrid-Reinforced Rubber-Coated Ballast and Natural Ballast Mix under Direct Shear Conditions

Rubber-coated ballast (RCB) is a new innovative ballast aggregate obtained by coating natural aggregates with recycled crumb rubber by using polyurethane binder. The objective of RCB is to reduce the ballast degradation, thereby reducing the deterioration of rail track geometry and also maintenance costs. Natural ballast; crumb rubber of sizes 0.4, 0.8, and 2 mm; Elastan polyurethane; and geogrid (triangular, 69 mm aperture size) were used in this study. The results of abrasion, impact value, and soundness tests show that RCB has a higher resistance to abrasion, impact, and weathering compared to natural ballast. Subsequently, the shear behavior and particle breakage of natural ballast, RCB, unreinforced, and geogrid-reinforced RCB–natural ballast mix was explored using the large-scale direct shear apparatus at different normal stresses and shearing rates (Sr). The test results indicate that due to rubber coating the peak friction angle (φ) of RCB samples reduces as compared to natural ballast. The reduction in φ of RCB samples is attributed to a change in surface texture. Moreover, 0.4-RCB (RCB made with rubber crumbs of size 0.4 mm) shows the least reduction in φ compared to 0.8-RCB and 2-RCB (RCB made with rubber crumbs of size 0.8 and 2 mm). It was further observed that with the increase in proportion of 0.4-RCB in geogrid-reinforced natural ballast both the peak friction angle and particle breakage (Bg) of ballast decreased significantly. The current study established the optimum content of 0.4-RCB to be mixed with geogrid-reinforced natural ballast to be in the range of 44%–53%.Practical ApplicationsThe problem of excessive degradation of ballast particles and the associated changes in the track geometry owing to the repeated application of heavy axle loads is addressed by coating the natural ballast with crumb rubber generated from waste tires. The rubber-coated ballast (RCB) is found to offer better abrasion, impact, and weathering resistance when compared to natural ballast. Moreover, it undergoes negligible particle breakage under direct shear conditions. The decrease in the extent of particle breakage helps in reducing the frequency of ballast replacement operations and hence tracks maintenance costs. Furthermore, RCB, when reinforced with geogrid, offers better shear strength than that of natural ballast alone. These observations imply that the tracks with geogrid-reinforced RCB can effectively reduce the risk of track instability.

Optimal design of sustainable recycled rubber-filled concrete using life cycle assessment and multi-objective optimization

This research studies the use of recycled crumb rubber (CR) as partial replacement for fine aggregates in concrete. Fracture analysis and Life Cycle Assessment (LCA) approach are used to assess 10 different Recycled Rubber-Filled Concrete (RRFC) mixtures by evaluating damage across 22 impact categories using the ReCiPe 2016 methodology. Multi-objective optimization (MOO) is deployed to identify optimal mixture proportions of RRFC using a BPNN-AGE-MOEA model. The MOO process considers concrete characteristic objectives, environmental assessment, and cost, while imposing boundary values for target compressive strength, water-to-cement (W/C) ratio, and CR content. The results show that increasing the CR content increases toughness and energy absorption capacity yet decreases the compressive and tensile strengths. Reducing the W/C ratio and increasing the CR content improved fracture characteristics and crack resistance. It is also found that the mechanical properties and the transportation stage of RRFC manufacturing have a significant effect on the environmental footprint. Careful material selection and transportation strategies can significantly reduce this environmental footprint. The proposed MOO approach using the predictive BPNN model successfully resolved the complex relationship between economic and environmental considerations of mixture design variables. To achieve a balance of environmental impact, affordability, and performance, the study underlines the need for carefully balancing the W/C ratio and CR content. The findings suggest that enhancing fracture properties while limiting the environmental impact is possible, allowing to promote wider application of recycled rubber in concrete.

Methodology for the environmental analysis of mortar doped with crumb rubber from end-of-life tires

The construction sector is in a process of improvement towards sustainability. The study of the use of a waste as raw materials is an opportunity. This article aims to evaluate the environmental viability of incorporating recycled crumb rubber from end-of-life tires into a mortar. To this end, a life cycle assessment tool is implemented by applying the EPD methodology to assess the various categories of impact. A series of mortar alternatives were analyzed in which fine aggregate is replaced by a percentage of crumb rubber ranging from 10% to 40%: the proportion increases by 5% in each solution. The scope of the LCA is from cradle to gate as it is during the various stages that the greatest environmental impacts are incurred: including the extraction of raw materials, their transport, as well as the production process. The functional unit is that of producing 1 m3 of mortar. The results obtained in this study show that the primary contributor to environmental impact is the cement production phase. On the other hand, the various alternatives evaluated achieved a 37.04% reduction in emissions of kg of CO2, as well as a 41.83% reduction of abiotic depletion of fossil fuels when 40% of fine aggregate was replaced by crumb rubber. This study also demonstrates that the transport distance of recycled materials from their point of production to the mortar production plant is a decisive factor. Depending on that distance, the proposed solution can be rendered environmentally unviable. On a final note, it is important to underscore that the appropriate use of recycled aggregates in mortar is not only determined by strength but also environmentally. This research generates knowledge about the environmental benefits of using recycled materials in construction.

Development of high performance geopolymer concrete with waste rubber and recycle steel fiber: A study on compressive behavior, carbon emissions and economical performance

Ultra-high performance concrete (UHPC) has good application prospects with its high strength, toughness and good durability performance. However, the high carbon emissions and high cost of its constituent materials are significant factors that limit its development and promotion. This study explores the development of a low-carbon and low-cost rubber modified high performance geopolymer concrete (R-HPGC) using recycled crumb rubber, recycled steel fibers, and low-carbon geopolymer gel. In this study, the compressive experiments of R-HPGC with different rubber volume replacement ratios (0, 5 %, 20 %, 35 %, and 50 %) were conducted to explore the laws and mechanisms of the effect of different rubber volume replacement ratios on the failure mode, compressive strength, deformation, and elastic modulus of R-HPGC. The compressive stress–strain model of R-HPGC considering the rubber replacement ratio were proposed. Meanwhile, a comprehensive evaluation method based on the carbon emission and cost index of concrete per unit strength is proposed to compare the carbon emissions and economical performance of R-HPGC, UHPC and normal concrete (NC). The results show that the compressive behavior of R-HPGC is determined by the mechanical properties and interactions between the mixed aggregates-geopolymer matrix-recycled steel fibers. At a low rubber replacement ratio (≤5 %/≤35 %), the compressive strength of R-HPGC can still reach the standard of ultra-high/high performance concrete (≥120 MPa/≥55 MPa). R-HPGC has a lower comprehensive cost and carbon emission index compared with conventional UHPC. NC has the lowest comprehensive cost index, but its comprehensive carbon emission index is the highest. It is recommended to use a rubber replacement ratio of ≤5 % for R-HPGC, which provides the best compressive mechanical performance, as well as excellent environmental and economical performance. This study provides a low carbon emission, low cost and high performance concrete that can be designed based on a combination of strength, carbon emission and cost.

Evaluation of fracture behavior of stone mastic asphalt (SMA) containing recycled materials under different loading modes at low temperatures

Using natural materials (including aggregates and bitumen) in the asphalt paving industry causes significant and irreparable damage to the environment annually. Utilizing waste materials in producing asphalt pavements can be a suitable solution to reduce such damages. Therefore, this paper studied the impacts of recycled crumb rubber (CR), recycled PVC particles, and reclaimed asphalt pavement (RAP) in different percentages on the performance of stone mastic asphalt (SMA) mixture against low-temperature cracking. PVC and CR additives were added to asphalt mix in two wet and dry methods. Thermal cracks are important and common failures of asphaltic pavements, and considerable financial budgets are allocated annually in different countries to deal with these damages. In this investigation, the fracture toughness of 16 various asphalt mixes at three distinct temperatures (temperatures of zero, −10, and −20° C) and under three diverse loading modes (including the mixed-mode I/ II, the pure mode II, and the pure mode I), were investigated by Semi-circular bending (SCB) fracture test. In addition to laboratory reports and mechanical studies, life cycle assessment (LCA) was utilized in this research to estimate and compare the influence of these asphalt mixes on the environment. The outcomes of mechanical tests and environmental analysis demonstrated that the usage of waste materials in this study has significantly enhanced the fracture strength of the SMA mix against low-temperature cracks and reduced its negative environmental effects. Therefore, the mixture containing RAP and 20% recycled PVC had the most satisfactory performance both in terms of environmental and fracture performance.

Rubber particle bridging effect on crack width control of low carbon Engineered Cementitious Composites (ECC)

Engineered Cementitious Composites (ECC) exhibit high tensile ductility and multiple cracking behaviors. The weak bonding between hydrophobic fiber and matrix tends to enlarge the crack width of ECC. This paper investigated recycled crumb rubber (CR) to tailor the crack width control of ECC as an artificial flaw. The experimental results show that CR can enhance the multiple cracking and reduce the crack width of ECC, which can be attributed to the CR weakened matrix and particle bridging effect. Micro-CT scanning revealed how CR influences the initiation and propagation of microcracks qualitatively. A constitutive model of CR particle bridging was developed to evaluate the quantitative contribution of CR particle bridging to the crack width reduction of ECC. Although the effect of bridging on crack width reduction is not as strong as that of the weakened matrix, the combined effect is consistent with the experimental magnitude of crack width reduction. Further parametric analysis indicates that small particle size, higher content, and narrower size distribution range of CR are preferred for better crack width control of ECC. The insights gained provide guidance on ECC composite design for a tight crack width with better durability properties.

Synergetic effects of recycled crumb rubber and glass cullet on the engineering properties of geopolymer mortar

The large amounts of waste glass and tires arouse a great interest in the use of recycled crumb rubber (RCR) and glass cullet (RGC) as fine aggregates. However, there are currently few studies regarding the influences of the combined use of RCR and RGC on the performances of geopolymer mortar, and their synergetic effects are still unclear. To fill this gap, this study investigated the engineering properties, microstructure, and eco-efficiency of geopolymer mortar incorporating RCR and RGC, with the mix ratios of 10:0, 7:3, 5:5, 3:7, and 0:10. The results showed that the synergetic use of RCR and RGC counteracted their adverse effects. The incorporation of RGC increased the relatively low flowability, compressive, and splitting tensile strengths as well as reduced the drying shrinkage caused by RCR. On the other hand, the incorporation of RCR improved the fresh density, flexural strength, high-temperature resistance, sorptivity, and chloride resistance degraded by RGC. These different influences of RCR and RGC on the performances were attributed to their distinct characteristics, i.e., the significantly lower water absorption, softer nature, and rougher surface of RCR than those of RGC. Besides, the bridging effect of attached microfibers on RCR particles was beneficial to improve flexural strength and high-temperature resistance. In addition, the geopolymer mortar showed significantly lower embodied CO2 emissions and embodied energy than the conventional one. The mix ratio of 30% RCR and 70% RGC is most recommended for applications because the shortcomings of RCR and RGC were minimized concurrently in this mix ratio.

Reduction of pavement thickness using a subgrade layer treated by different techniques

A range of stabilisers for poor quality subgrade soils have been developed to promote road constructions. Many of them are becoming more popular depending on their effectiveness. The purpose behind this research is to identify the relative efficacy of many physical and chemical stabilisation techniques for enhancing the properties of three types of local Iraqi subgrade soils. The comparison of the samples is based on the CBR tests. The AASHTO (1993) flexible pavement design was used to compute the pavement thickness requirements. The soil samples A, B and C have a natural CBR values of 3.8, 3.9 and 4, respectively, on which the physical stabilisers of Powdered rock (PR), grained recycled concrete (GRC), and recycled crumb rubber grains (CR) were employed, while Quicklime (QL) and activated fly ash (AFA) were both utilised as chemical stabilisers. The stabilisation with 15 % of AFA proved to be the most applicable method for soil types A and B for reducing the pavement thickness requirements by 51 % and 32 %, respectively, with a reasonable financial feasibility for both. The same feasibility is proven when stabilising soil type C with 15 % of GRC, which reduces the pavementthickness by 25.7 %.

Recycling waste vehicle tyres into crumb rubber and the transition to renewable energy sources: A comprehensive life cycle assessment

This study conducts a comprehensive life cycle assessment (LCA) on converting waste vehicle tyres into recycled crumb rubber (CR) granules as an alternative polymer for enhancing asphalt properties. The LCA study has been performed on acquired industrial primary data by incorporating CR at different proportions of binder in one ton (1-ton) of asphalt mix following the wet method. The uncertainty analysis of design variables identified a relatively strong positive relation of emissions with the equipment energy consumption (r = 0.98). Monte Carlo simulations evaluate the potential renewable sources (solar, hydro, and wind) in sequence over fossil fuels for the possible transition in the Australian grid by 2030 and 2050, as per the Paris Agreement. 71.91% reduction of CO2 emissions is achievable by recycling vehicle tyres into crumb rubber compared to landfill and incineration. Recycling by-products of CR production, such as steel and textile, significantly mitigates negative impacts. A decrease of 2.23% emissions was associated to the use of crumb rubber as a binder modifier in the asphalt mixture via the midpoint assessment. In endpoint LCA, a higher association of resource (US$) saving costs was observed than for other protective zones, i.e., human health and ecosystem damage. Recycling 466,000 tonnes of disposable waste tyres contributes to 16.1 million US$ worth of resource savings. An equitable industry-based LCA and uncertainty analysis of design parameters can assist in prioritizing suitable options to improve efficiency and future emission strategies on a global scale.