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Road paving costs have significantly increased in the last decades not only because of the increase in oil price globally, which has in turn increased the prices of bitumen, transportation, coarse aggregate and fine aggregate, but also due to the shortage of these virgin materials. Thus, it is essential to find more sustainable and cost-effective road paving solutions. This research focuses on the combination of recycled asphalt pavement (RAP) and crumb rubber extracted from end-life tires and new asphalt mixtures to assess the enhancement of asphalt performance and cost minimization. The optimal percentage of RAP mixed with new asphalt including crumb rubber with achieves the highest performance, stability, and durability of pavement, while considering the economic and environmental impacts was investigated. Experimental investigations, including a universal testing machine and the Marshall stability test, were implemented to evaluate different mixing percentages of RAP and the new asphalt including crumb rubber at different bitumen contents. Abaqus software was utilized to simulate a model with the new mixture to determine the stress and deformation characteristics under different loading conditions. The findings of the experimental study from testing more than 150 samples of asphalt with different percentages of mixing illustrated that a balanced mix of 50% RAP with 50% new rubberized asphalt with a 5% bitumen content achieved the optimal balance of stability, flow and density characteristics, which will offer a promising solution for more sustainable and cost-effective road-paving solutions. [ABSTRACT FROM AUTHOR]

This study investigated the performance of rubberized asphalt mixtures through Marshall and wheel track tests. The optimal binder content for rubberized asphalt specimens containing 6 and 8% rubber was determined to be 4.9 and 5%, respectively, while the control asphalt required 4.6% binder content. The results indicate that modifying the binder with crumb rubber improves the properties of the asphalt mixture. The wheel track tests show that the rubberized asphalt samples have far shallower ruts than the control samples, demonstrating successful protection against long-term distortion. Rubberized asphalt is more resistant to rutting at higher temperatures, with lower sustained strain rates and shallower ruts. Adding crumb rubber enhances the stiffness and viscosity of the asphalt binder, contributing to the improved rutting resistance of the rubberized asphalt mixtures. This study emphasized the potential of rubberized asphalt as a sustainable solution for enhancing pavement durability and longevity. The findings highlight the benefits of using rubberized asphalt in pavement engineering and provide valuable insights for optimizing binder content and improving performance. Incorporating crumb rubber in asphalt mixtures can reduce rutting and enhance the overall sustainability of pavement surfaces.

Asphalt pavements are consistently subjected to environmental and loading conditions that affect their durability, such as oxidative aging. Modification of the pavements assists in reducing the aginginduced stiffness. One of these solutions is crumb rubber (CR)-modified warm mix asphalt (WMA) binders. This study aims to assess the long-term performance and effects of aging on CR-modified WMA binders through a series of physical, rheological, and chemical tests. 2% and 4% of Sasobit, a wax-based additive, and 1.5% and 3% of Zycotherm, a nano-based chemical additive, with 10%, 15%, and 20% CR, were utilized. The binders were aged using a rolling thin film oven (RTFO) and pressurized aging vessel. The unaged and long-term aged asphalt binders were tested. Rheological properties, using master curves and zero shear viscosity, physical properties measured through elastic recovery, along with chemical analysis using Fourier transform infrared (FTIR) spectroscopy, were carried out on the binders before and after aging. Based on the physical and rheological aging indices, Sasobit-modified asphalt binders exhibited superior resistance to aging and rutting compared to Zycotherm-modified binders. Specifically, the Sasobit 4% and 20% crumb rubber blend showed the highest resistance to physical aging, while Zycotherm-modified binders demonstrated improved chemical aging resistance. Adding crumb rubber significantly enhanced the stiffness and elasticity of the asphalt binders, further reducing the effects of aging. FTIR analysis confirmed that Sasobit and crumb rubber reduced oxidation and volatile component loss during aging. [ABSTRACT FROM AUTHOR]

This report presents the initial performance of the Woodland SR 113 thin concrete overlay on asphalt (COA) project built in 2018-2019.The project comprises approximately four miles of a two-lane highway. The COA had 6 ft. transverse joint spacing, a slab thickness of 6in., and an asphalt base that was overall in very poor condition. The performance of the project between the date of construction andOctober 2020 is presented in this report. The performance was evaluated by different means, including periodic visual inspections andlongitudinal profiler evaluations; falling weight deflectometer (FWD) testing; real load testing (RLT), where the concrete strains undertruck loading were recorded; and continuous monitoring of slab temperatures and drying shrinkage deformations. Overall, the projectperformed as expected. Visual inspection of the COA did not indicate any cracking, faulting, or other structural distress. FWD and RLTevaluations indicate that the COA structure has remained stable since the construction. While the smoothness varied considerably during the period evaluated in this report, the variation was caused by changes in slab curvature due to thermal gradients through the slab depthand concrete drying shrinkage.

Road paving costs have significantly increased in the last decades not only because of the increase in oil price globally, which has in turn increased the prices of bitumen, transportation, coarse aggregate and fine aggregate, but also due to the shortage of these virgin materials. Thus, it is essential to find more sustainable and cost-effective road paving solutions. This research focuses on the combination of recycled asphalt pavement (RAP) and crumb rubber extracted from end-life tires and new asphalt mixtures to assess the enhancement of asphalt performance and cost minimization. The optimal percentage of RAP mixed with new asphalt including crumb rubber with achieves the highest performance, stability, and durability of pavement, while considering the economic and environmental impacts was investigated. Experimental investigations, including a universal testing machine and the Marshall stability test, were implemented to evaluate different mixing percentages of RAP and the new asphalt including crumb rubber at different bitumen contents. Abaqus software was utilized to simulate a model with the new mixture to determine the stress and deformation characteristics under different loading conditions. The findings of the experimental study from testing more than 150 samples of asphalt with different percentages of mixing illustrated that a balanced mix of 50% RAP with 50% new rubberized asphalt with a 5% bitumen content achieved the optimal balance of stability, flow and density characteristics, which will offer a promising solution for more sustainable and cost-effective road-paving solutions.

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The costs of producing asphalt mixtures are increasing day by day, and with the expansion of roads, the use of natural resources of aggregates has also increased. On the other hand, several factors, such as the increase in traffic load and the number of vehicles, intensify the stress in the pavement layers, reduce the service life of asphalt pavements, and increase the cost of maintenance of road pavements. For this reason, researchers are striving to reduce the costs of asphalt mixture production and the need for natural aggregates by taking advantage of rubberised asphalt in this field. However, when using rubber powder as aggregate, some weaknesses are observed in this mixture, which this study strives to solve by modifying bitumen and improving its performance. The objective of this study is to evaluate the effect of bitumen modified with Nano-SiO2 on the mechanical properties of rubberised asphalt mixture. The percentages of Nano-SiO2 are 0, 0.3, 0.6, 0.9, and 1.2% by weight of bitumen, and used rubber powder has been replaced with fine aggregates with different percentages of 0, 1, 3, and 5%. The characteristics investigated in this study are rutting and fatigue, evaluated in various laboratory conditions. Considering all three target criteria of this study (i.e. environmental, economic and technical), an asphalt mixture containing 3% rubber powder and 1.2% Nano-SiO2 can be considered the best combination to deal with rutting and fatigue. A combination by replacing 3% of aggregates with rubber powder, needs less to extract natural aggregates resources, and also the use of a waste material whose depot in nature is known as an environmental problem in the construction of new asphalt mixture. In addition to environmental aspects, This sample fatigue resistance is about 5%, and the rutting resistance is about 17% more than the control specimen (without additives). [ABSTRACT FROM AUTHOR]

The costs of producing asphalt mixtures are increasing day by day, and with the expansion of roads, the use of natural resources of aggregates has also increased. On the other hand, several factors, such as the increase in traffic load and the number of vehicles, intensify the stress in the pavement layers, reduce the service life of asphalt pavements, and increase the cost of maintenance of road pavements. For this reason, researchers are striving to reduce the costs of asphalt mixture production and the need for natural aggregates by taking advantage of rubberised asphalt in this field. However, when using rubber powder as aggregate, some weaknesses are observed in this mixture, which this study strives to solve by modifying bitumen and improving its performance. The objective of this study is to evaluate the effect of bitumen modified with Nano-SiO2 on the mechanical properties of rubberised asphalt mixture. The percentages of Nano-SiO2 are 0, 0.3, 0.6, 0.9, and 1.2% by weight of bitumen, and used rubber powder has been replaced with fine aggregates with different percentages of 0, 1, 3, and 5%. The characteristics investigated in this study are rutting and fatigue, evaluated in various laboratory conditions. Considering all three target criteria of this study (i.e. environmental, economic and technical), an asphalt mixture containing 3% rubber powder and 1.2% Nano-SiO2 can be considered the best combination to deal with rutting and fatigue. A combination by replacing 3% of aggregates with rubber powder, needs less to extract natural aggregates resources, and also the use of a waste material whose depot in nature is known as an environmental problem in the construction of new asphalt mixture. In addition to environmental aspects, This sample fatigue resistance is about 5%, and the rutting resistance is about 17% more than the control specimen (without additives). [ABSTRACT FROM AUTHOR]

This report documents the design and construction of a concrete overlay on asphalt (COA) pavement on State Route 113 in Woodland, California, one of the first COA projects in the Caltrans road network. The project site extended over approximately 4 mi. of a two-lane secondary road. The concrete slabs were a half-lane wide (6×6 ft.) and 6 in. thick. The transverse joints were undoweled, but tie bars were installed at all the longitudinal joints. The outside slabs were 2 ft. wider than the interior slabs to provide a concrete shoulder. The project included a section with newly placed, rubberized, gap-graded asphalt mix base. A rapid-strength concrete mixture with Type II/V portland cement designed to be opened to traffic in 24 hours was used for construction of the overlay. The northern part of the project (PM 14.760 to PM 17.580) was built in October and November 2018, while the southern part (PM 11.860 to PM 12.890) was built in April and May 2019. The concrete mixture was produced in a fixed plant and transported in ready-mix trucks 25 mi. to the construction site. A slipform paver was used to consolidate and finish the concrete. A number of the quality control/quality assurance (QC/QA) tests and evaluations summarized in this report were conducted before, during, and after the construction of the concrete overlay. These QC/QA tests and evaluations revealed no major design or construction issues with the concrete overlay, but they did show that the condition of the asphalt base was very poor, particularly in the northern part of the project.

Rubberized thin surfacing hot mix asphalt (RTSHMA) is a type of flexible pavement that is currently being developed. It can provide the same good performance as asphalt concrete-wearing course (AC-WC). Based on previous research, the use of crumb rubber in the asphalt mixture can provide several advantages, such as increasing the flexibility of the mix so that the pavement is more resistant to cracking. Based on research showing the advantages of rubberized asphalt, the idea emerged to apply it in the field, namely on the Palur-Sragen City Boundary section as wearing course. The method of analysis in this study was modeling the pavement structure with the KENPAVE and BISAR 3.0 programs. The analysis results showed that the AC-WC model and RTSHMA model have the same good performance because both of them have a service life of more than twenty years, which is the standard for flexible pavements. However, RTSHMA has an advantage, i.e., the thickness layer is 25% thinner than AC-WC's. With a thinner layer than AC-WC but the same good performance, RTSHMA is worth considering as an alternative pavement, especially for overlays. [ABSTRACT FROM AUTHOR]

The content of ground tire rubber was limited by its multiple cross-linking networks. High-content ground tire rubber modified asphalt （mass fraction of ground tire rubber more than 30%） binder could be produced by addition of degraded tire rubbers （DR）, which was controllably prepared by reactive screw extrusion using ground tire rubber. The effects of degradation degree and content of DR on structure and properties of DR modified asphalt were analyzed by Soxhlet extraction, Mooney visco-sity, basic physical properties, infrared spectroscopy, and optical microscopic tests. The results showed that chemical bonds broke, and cross-linking network of ground tire rubber collapsed during degradation process. Compared with conventional ground tire rubber modified asphalt binder, DR modified asphalt binder had finer dispersion, lower viscosity and better stability at high temperature. The addition of DR with high degree of degradation increased by a large margin the content of ground tire rubber, leading to further improved deformation ability at low temperature and deformation resistance at high temperature. The steep increased of viscosity at certain rubber content should be noticed.

Thin bonded concrete overlay of asphalt (BCOA) is a rehabilitation alternative consisting of a 100 to 175 mm (0.33 to 0.58 ft) thick portland cement concrete (PCC) overlay of an existing flexible or composite pavement. Fifteen BCOA sections were built at the Davis facilities of the University of California Pavement Research Center in February 2016. Eleven of these full-scale sections were tested under accelerated loading, while four of them were used for monitoring the response of BCOA to the ambient environment and cement hydration. This full-scale experiment is part of a research project whose primary goal is to develop recommendations and guidance on the use of thin BCOA as a rehabilitation alternative in California. The design and construction of these sections is presented in this report, together with results from the quality control/quality assurance testing that was conducted. This testing was focused on the four early high-strength mixes that were used in the construction. The concrete mixes included Type II/V and Type III portland cements and calcium sulfoaluminate cement, and they were designed to provide 2.8 MPa (400 psi) flexural strength after either 4 or 10 hours. Concrete overlays were built either on top of old asphalt pavements that had been tested for another research project or on top of a new gap-graded rubberized hot mix asphalt (RHMA-G) layer. Three slab sizes were built: 1.8x1.8 m (6x6 ft), 2.4x2.4 m (8x8 ft), and 3.6x3.6 m (12x12 ft). This report also describes the instrumentation of the sections and evaluates the engineering reasonableness of the initial data collected by the sensors up to August 2016. There are no recommendations presented in this report. Recommendations regarding implementation of BCOA will be included in the final report of this project.

The use of waste tires to prepare rubberized asphalt has been a hot trend in recent years, and the characteristics of adhesion between rubberized asphalt and aggregates are important factors affecting the performance of asphalt pavement. However, there is a lack of uniform results on the adhesion characteristics of rubberized asphalt. Therefore, crumb-rubber-modified asphalt (CRMA) with 15%, 20%, and 25% rubber contents was prepared in this work, and the basic rheological parameters and cohesive energy of the rubberized asphalt were characterized by DSR. The adhesion properties between rubberized asphalt and aggregates were characterized based on macroscopic binder bond strength (BBS), surface free energy (SFE) theory, and nanoscale atomic force microscopy (AFM) tests. The results show that crumb rubber (CR) can improve the high-temperature elastic properties of asphalt; secondly, CR can have a negative impact on the maximum tensile strength of asphalt and aggregates. CR can improve the SFE parameter of asphalt. The work of adhesion of rubberized asphalt and limestone is the highest, followed by basalt and, finally, granite. Finally, CR can cause the catanaphase in asphalt to gradually break down and become smaller, and the adhesion of rubberized asphalt can be reduced. Overall, CR can reduce the adhesion performance of asphalt, and this work provides a reference for the application of rubberized asphalt. [ABSTRACT FROM AUTHOR]

The ability to anticipate the effects of the interaction between waste rubber particles from end-of-life tires and bitumen can encourage the use of rubberized bitumen, a material with proven environmental benefits, in civil engineering applications. In this study, a predictive model of rubberized bitumen viscosity is presented for this purpose. A machine learning-based approach (Multi-Gene Genetic Programming—MGGP) and a more traditional multi-variable least square regression (MLSR) method are compared. The statistical analysis indicates that the robustness and the capability of the MGGP algorithm led to a better estimation of the rubberized bitumen's viscosity. Additionally, the MGGP analysis returned an actual equation that could be easily implemented in any spreadsheet for an initial tuning of the production protocol based on the desired level of interaction between the rubber and bitumen. [ABSTRACT FROM AUTHOR]

Rubber asphalt has always been considered to have the most potential for the disposal of waste tires as sustainable infrastructure. However, the covalently cross-linked tire rubber presents an extreme challenge in reusing waste rubbers in roads. Rubberized asphalt with finely dispersed or colloidal structure has been regarded as a potential binder used as road material because of the improved properties in terms of storage stability, easy processing and high content of incorporation. However, the mixing mechanism between the finely dispersed rubber on micro-nano scale with asphalt is still not clear, which restricts its further development as value-added material. Devulcanized rubber (DR) was introduced to improve the compatibility between asphalt and rubber. The basic chemicals of DR and asphalt were introduced based on their structures. Furthermore, the interactions between DR and asphalt were discussed according to the functional elements at different levels, and the concept of DR as "the fifth component" of asphalt was put forward. Finally, high performance, environmental and economic effects and applications of devulcanized-rubber-modified asphalt (DRMA) were discussed. The review is expected to provide a guide for the wide application of DRMA, which is still restricted by poor compatibility and bad stability during processing, storage and recycling. [ABSTRACT FROM AUTHOR]

The asphalt pavement in the Middle East suffers from numerous problems, such as high traffic load, critical climate changes, poor construction quality, and economic problems. These reasons drove researchers to develop modified asphalt binders with excellent performances at a relatively lower cost. Crumb rubber (CR) still has in its early stages in the Middle East countries as an asphalt modifier. The objective of this review is to understand the effect of CR on the performance of asphalt binder and asphalt mixture used in the Middle East countries. The application of CR through the wet process improved the rutting, cracking, and aging resistance of the asphalt mixture. The combination of CR and other materials, such as Styrene–Butadiene–Styrene and Reclaimed Asphalt Pavement, further enhanced the properties of rubberized asphalt. It can be concluded that pavement implemented with rubberized asphalt technology is promising in the Middle East, as it is much more effective than conventional asphalt or other polymer-modified asphalt. For future study, the elasticity modulus and tensile strength of rubberized asphalt in the Middle East are recommended, and the durability of constructed pavement using CR should be evaluated. [ABSTRACT FROM AUTHOR]

The self-healing ability of rubberized asphalt, especially at low-temperatures, plays a vital role in extending the durability of pavements. Despite the wide use of rubberized asphalts, the impact of the degradation degree of crumb tire rubber (CTR) on self-healing behavior of rubberized asphalt remains unclear. In this study, we conducted a controlled degradation of CTR through screw extrusion to examine the effects of degradation degree and CTR dosage on the self-healing behavior of the rubberized asphalt. The self-healing ability of different rubberized asphalts was investigated by ductility tests and tensile tests conducted with a dynamic thermo-mechanical analyzer. The results revealed that the content of CTR and its degradation significantly affected the compositional structure and healing ability of the modified asphalt. The rubberized asphalt with highly degraded crumb tire rubber (DCTR) exhibited the best flow healing ability due to the fine dispersion of DCTR in asphalt and the highest value of loss factor at low temperatures. Conversely, the asphalt modified with the lightest DCTR exhibited higher healing efficiency at higher temperatures, attributed to more dynamic sulfur bonding and re-crosslinking of rubber molecular chains. This study provides a better understanding of the road healing performance of rubberized asphalts with different degradation degrees of CTR. [Display omitted] • The degradation of tire rubber affected on self-healing behavior. • The self-healing properties were investigated at both high and low temperatures. • The ratio of fracture energy was proposed to characterize the self-healing. • Rheological fluid and rubber molecular interactions promoted self-healing. [ABSTRACT FROM AUTHOR]

The high-temperature rheological properties of rubberized asphalt and mixture were evaluated by frequency scanning, repeated creep recovery (RCR) test, temperature sweep test, Hamburg wheel tracking test (HWTT). Based on the Pearson correlation coefficient, the correlation of the mixture gradation and asphalt characteristics with the high-temperature stability of the mixture was analyzed. Finally, the gray correlation theory was applied to analyze the evaluation indexes of the high-temperature rheological properties of rubberized asphalt and mixture. The results show that the asphalt-stone ratio and the fractal dimension (Dc) of coarse aggregate have a significant correlation with the high-temperature performance of the mixture, and the mixture with a smaller asphalt-stone ratio and a higher percentage of coarse aggregate has a better high-temperature performance. The correlation degree of softening point, viscous stiffness modulus and permanent deformation with rubber-asphalt mixture is higher than 0.7, and are significantly higher than those of rotational viscosity at 180°C. Therefore, we recommend the use of permanent deformation, softening point, and viscous stiffness modulus to evaluate the high-temperature performance of rubberized asphalt mixture.

In order to explore the effect of aggregate type on the interface interaction between rubberized asphalt and aggregate, the representative molecules of base asphalt, rubberized asphalt, limestone (calcite), basalt (augite), and granite (quartz) were modeled by a molecular dynamics method. Additionally, asphalt–aggregate interface models were constructed by using the existing molecular models. The interface interaction between rubberized asphalt and different aggregates was analyzed by the radial distribution function (RDF), diffusion coefficient and adhesion energy density, and the simulation results were verified by a surface energy test. The results show that the interaction between asphalt and aggregate exists in the form of hydrogen bond, and the polarity of asphalt and aggregate has a great influence on the interaction. Calcite has the strongest interaction with asphalt among the three crystalline molecules. This conclusion further explains the phenomenon that alkaline aggregate has better adhesion to asphalt. The interaction between augite and crumb rubber is relatively strong, which leads to the maximum enhancement of the interaction between rubberized asphalt and augite. This study provides a reference for further research on the formation and failure of asphalt–aggregate interface interactions under various conditions and environments. [ABSTRACT FROM AUTHOR]

The depletion of natural aggregate sources which generally accounts for a huge percent of Hot Mixed Asphalts (HMAs) and the difficulty posed by disposal scrap tires are a major environmental concern for the future. The use of waste products like scrap tires in highway construction is considered a sustainable way of dealing with these issues. Crumb rubber is a material pulverized from waste polymer products like scrap tires which are then added to HMAs to improve their performance. This study focuses on the sensitivity of crumb rubber particle sizes (fine ≤1.18 mm), (coarse ≥1.18 mm and ≤3.35 mm) (and mix of 50% fine and 50% coarse) and partial replacement (1.5 and 2.5% of total weight) of aggregates on the Marshall test parameters of rubberized asphalt mixes. The Marshall test parameters: density, stability, VTM, VFB of both rubberized asphalt and conventional asphalt samples were compared and also the Asphalt Institute (AI) and National Asphalt Pavement Association (NAPA) methods were used to obtain the optimum bitumen content (OBC). From the results, it suggests that; the utilization of dry process methodology of adding crumb rubber additives in different sizes and percentages had a considerable effect on Marshal test parameters and also influences the optimum binder content estimates. The results of this study can be used as a reference point for the use of crumb rubber in HMAs.

The crumb rubber (CR) derived from waste tires has been used widely to prepare rubberized asphalt for paving applications. However, rubberized asphalt severely suffers from poor compatibility and consequent storage instability. Therefore, a solution soaking pretreatment was used to activate the CR surface to improve the compatibility of rubberized asphalt in this study. Three different solutions—water, sodium hydroxide, and sulfuric acid—were employed. The Fourier-transform infrared spectroscopy (FTIR) spectra indicated the removal of zinc stearate from the CR surface after solution soaking. Consequent improvement of the surface hydrophilicity of CR was found from the promoted sedimentation in water and the reduced water contact angle. Dynamic dhear rheometer (DSR) test results showed that the effect of solution soaking on the rheology of rubberized asphalt was slight. However, according to the results of the segregation test and a novel drainage-based method, the solution soaking pretreatments significantly improved the compatibility of rubberized asphalt. This was reflected directly in the reduced segregation degree and promoted CR/asphalt interactions. The solution soaking pretreatment of CR had no adverse effect on the moisture susceptibility of rubberized asphalt according to the modified binder bonding strength (BBS) test results. Of the three pretreatments, sodium hydroxide performed best, followed by sulfuric acid and water. [ABSTRACT FROM AUTHOR]

Purpose: It is estimated that in Colombia around 25 million tires are disposed of yearly. The management of discarded tires is still a major problem considering that 3 of 10 disposed tires end up on sidewalks, separators, parks, wetlands, and even in front of houses. Additionally, mainly in urban and suburban zones near the main roads, noise is one of the central factors that affect people's quality of life. In this article, a life cycle assessment (LCA) from cradle to grave of rubberized and conventional asphalt pavements was employed to quantify the consequences associated with the implementation of the alternative technology and the present engineering practices. LCA was performed involving the local materials and available machineries in Colombia, and the inclusion of traffic noise as part of the LCA. Methods: LCA in this study involves two methods: attributional LCA (ALCA) and consequential LCA (CLCA). To include the effect of traffic noise in the LCA, a methodology developed by the Swiss author Gabor Doka (2003) was used. Estimation of material's quantities and their characteristics, noise levels, logistics, and production were done based on a Colombian case study. Results and discussion: Damage assessment showed that conventional asphalt (CA) impacts 67% more in human life than rubberized asphalt (RA). Traffic noise assessment results presented that CA has about 38% more impact in human life compared with RA, then, considering the study period (25 years), a reduction of 2.8 dB in noise emission due to the implementation of RA represents a considerable positive impact in human life. The total effect in ecosystems showed that CA has 40% more impact in the extinction rate of species than RA. In total, CA causes 43% more impact in resources than RA. Consequential assessment showed that the implementation of the RA represents 48% less environmental damage than the conventional alternative. Conclusions: RA is a more environmentally friendly alternative compared with CA because it requires less raw material usage, and less mix production due to its better performance (less maintenance and rehabilitation interventions). RA represents a suitable alternative to divert tons of used tires from the landfills. [ABSTRACT FROM AUTHOR]

The pre-swollen crumb rubber (PSCR) is a pelletized rubber produced by the reaction of scrap tire rubber particles with bitumen-compatible oil at elevated temperatures. It does not require a prior blending with bitumen, and it can be added directly at an asphalt plant. A laboratory investigation was carried out to evaluate the performance of plant-produced PSCR modified mixtures for surface and intermediate courses and analyze their suitability for low-traffic volume road in cold environment applications. Linear viscoelastic properties, rutting and thermal cracking performance were investigated in the laboratory. The presence of pre-swollen rubber particles and, in particular, the bitumen-compatible oil softened the mixtures as indicated by the dynamic modulus master curves. The different mechanical responses led to an enhancement of thermal cracking resistance but increased the rutting susceptibility of the PSCR mixtures. Despite the laboratory findings, no rutting was observed after five years of service life based on visual inspection of the field test sections constructed in Michigan with PSCR-modified Hot-Mix Asphalt (HMA). A few transverse cracks were generated in the lanes where the control mix with neat bitumen was used. Those cracks did not propagate into the PSCR modified material, in agreement with the laboratory findings. [ABSTRACT FROM AUTHOR]

The depletion of natural aggregate sources which generally accounts for a huge percent of Hot Mixed Asphalts (HMAs) and the difficulty posed by disposal scrap tires are a major environmental concern for the future. The use of waste products like scrap tires in highway construction is considered a sustainable way of dealing with these issues. Crumb rubber is a material pulverized from waste polymer products like scrap tires which are then added to HMAs to improve their performance. This study focuses on the sensitivity of crumb rubber particle sizes (fine ≤1.18 mm), (coarse ≥1.18 mm and ≤3.35 mm) (and mix of 50% fine and 50% coarse) and partial replacement (1.5 and 2.5% of total weight) of aggregates on the Marshall test parameters of rubberized asphalt mixes. The Marshall test parameters: density, stability, VTM, VFB of both rubberized asphalt and conventional asphalt samples were compared and also the Asphalt Institute (AI) and National Asphalt Pavement Association (NAPA) methods were used to obtain the optimum bitumen content (OBC). From the results, it suggests that; the utilization of dry process methodology of adding crumb rubber additives in different sizes and percentages had a considerable effect on Marshal test parameters and also influences the optimum binder content estimates. The results of this study can be used as a reference point for the use of crumb rubber in HMAs. [ABSTRACT FROM AUTHOR]

Because there is a lack of studies on rubberized asphalt based on silane coupling agent modification, KH-550 modified crumb rubber and rubberized asphalts incorporating normal rubber and modified rubber were prepared, respectively. The rheological properties of asphalt samples were evaluated by a dynamic shearing rheometer and a bending beam rheometer; then, mechanisms of KH-550 on rubber surface and functional group changes were analyzed by a Brunauer–Emmett–Teller specific surface area measurement and a Fourier transform infrared spectroscopy. The results imply that: (i) rubber surface area rises and chemical reactions accrue between rubber and asphalt; (ii) modified rubber achieves a more stable state within asphalt, which helps to enhance the mechanical properties of asphalt; (iii) modified rubber helps asphalt to dissipate stress so as to resist the formation of cracks and deformation under low temperature conditions. [ABSTRACT FROM AUTHOR]

The proposed bio-modified rubberized asphalt (BMRA) technology integrates bio-oil and crumb rubber modifications, offering cost savings, waste reuse, improved asphalt performance, and reduced asphalt consumption. Like traditional asphalt, BMRA ages over time due to external environmental factors, impacting its pavement performance. This study examines the alterations in rheological and low-temperature characteristics of BMRA during thermal-oxidative aging. Results indicate that incorporating bio-oil minimizes alterations to the complex modulus and phase angle in aged asphalt. BMRA's crossover modulus significantly surpasses that of unaged rubberized asphalt (RA), showcasing the mitigating effect of bio-oil and crumb rubber on asphalt's rheological properties during aging. BMRA demonstrates comparable or enhanced peak load, fracture displacement, fracture toughness, and fracture energy relative to RA. BMRA's glass transition temperature remains lower than that of other unaged asphalts, signifying enhanced resistance to low-temperature cracking even after aging. Bio-oil, characterized by low molecular weight and abundant light components, counteracts performance deterioration attributed to volatile constituents and destabilization of asphalt's colloid structure during aging. Crumb rubber facilitates the absorption and subsequent release of specific light components, augmenting BMRA's resistance to aging. These findings enhance our understanding of the mechanisms governing the aging resistance and performance of bio-modified rubberized asphalt, thereby supporting the development of sustainable and durable asphalt materials. [Display omitted] • Bio-oil and CR mitigate asphalt deterioration during thermal-oxidative aging. • Bio-oil offsets light components volatility and stabilizes asphalt colloid structure during aging. • Absorption and release of light components by CR enhance asphalt aging resistance. [ABSTRACT FROM AUTHOR]

Highlights • Specific surface treatment was applied on rubbers to produce rubberized asphalt. • High temperature rheological performances were studied at virgin and RTFO state. • High temperature rheological characteristics get significant promotions. • Short term aging positively affects high temperature rheological characteristics. Abstract Crumb rubber modified asphalt has gained growing interest as environmental friendly binder in last few decades. The objective of this study was to investigate a new treatment method of crumb rubber impact on the high temperature rheological performances of modified binders produced with two base binders and six crumb rubbers at virgin and the RTFO states. Firstly, FTIR test was conducted to determine the functional groups in all rubbers. For all of the binders, the viscosity value, failure temperature, rutting resistance factor, storage modulus and phase angle were obtained by the rotational viscometer and dynamic shear rheometer at different temperatures and aging states. FTIR curves showed that S O appeared after rubber surface treatment. The results illustrated that the high temperature rheological properties of all rubberized binders tested in this research project were improved regardless of binder and rubber sources as well as rubber type. In addition, the treatment is only recommended to be applied on the typical rubber to get promotions towards rheological performances at high temperatures. On the other hand, short term aging resulted in positive effect on these performances. [ABSTRACT FROM AUTHOR]

The focus of this paper is to evaluate the energy consumption and environmental impact of rubberized asphalt pavement during the life cycle. Reducing the environmental influences of the highway infrastructure has received the increasing attentions recently. Application of crumb rubber in asphalt pavements overcomes the used tires disposal problem and achieves materials savings and environmental benefits, due to the reduction of raw material and extension of pavement service life. In addition, rubberized asphalt production is a highly energy consuming process due to a higher mixing temperature. However, the warm mixing technology can lower the mixing temperature of rubberized asphalt mixture, leading to approximately 20–25% of fuel savings. Moreover, the consumed energy of rubberized asphalt during maintenance phase is lower than that of conventional asphalt. In addition, the greenhouse gas (GHG) emissions from the production and construction of rubberized asphalt mixtures are similar to those from hot mix asphalt, but their emissions of CO and CH 4 are much lower. Meanwhile, the noise reduction is an environmentally friendly benefit. The leachate from asphalts used wet and dry-process crumb rubber modifiers (CRM) does not pose a measurable threat to the environment. Rubberized asphalt technology as a green technology in term of lowering GHG emissions, saving energy and raw material and reducing noise level of pavement should be widely used to achieve environmental sustainability. [ABSTRACT FROM AUTHOR]

Because there is a lack of studies on rubberized asphalt based on silane coupling agent modification, KH-550 modified crumb rubber and rubberized asphalts incorporating normal rubber and modified rubber were prepared, respectively. The rheological properties of asphalt samples were evaluated by a dynamic shearing rheometer and a bending beam rheometer; then, mechanisms of KH-550 on rubber surface and functional group changes were analyzed by a Brunauer−Emmett−Teller specific surface area measurement and a Fourier transform infrared spectroscopy. The results imply that: (i) rubber surface area rises and chemical reactions accrue between rubber and asphalt; (ii) modified rubber achieves a more stable state within asphalt, which helps to enhance the mechanical properties of asphalt; (iii) modified rubber helps asphalt to dissipate stress so as to resist the formation of cracks and deformation under low temperature conditions.

Low resistance against dynamic loads and short service life of pavement are the most significant problems in the conservation and maintenance of roads, to the extent that, annually enormous costs are spent in order to improve capabilities of road services in the country. Research shows that the use of some wastes such as waste rubber powder in asphalt mixtures not only increase its serves life but also cause to reduce production costs; furthermore, recycling the crumb rubber has also considerably environmental benefits environmental benefits such as reduced need for landfill, less atmospheric pollution from burning. In this paper, the effect of adding waste rubber powder on the rutting performance of asphalt mixtures has been studied. In order to compare the performance of rubberized asphalt mixtures and conventional asphalt, wheel track test has been used. The results of this study show that the use of rubber powder caused a significant decrease in the rate of rutting depth of rubber asphalt mixtures compared to control samples.

Traffic noise is one of the most serious concerns to issues related to environmental quality in many urban communities throughout the world. The current research paper is dealing with measurements on environmental noise in pavements of urban road sections with bituminous mixtures made of rubberized asphalt. Specifically, measurements are made in two roads’ sections of different geometric, operational and traffic characteristics in the city of Lamia in Greece. Data are compared in both sections and in parts made of conventional and rubberized asphalt surface layer, while conclusions concerning the effect of rubberized asphalt layers in noise pollution are monitored. This research follows the European Project with the acronym ROADTIRE, co-funded by the European Commission, and it has been funded by General Secretariat of Research and Technology (GGET).Results certify that rubberized asphalt layers provide a safe, cost effective road surface and environmentally friendly option of pavement.Rubberized bituminous mixtures could be agood solution for the re-surfacing of any street which is in poor condition, since not only does it reduce noisegeneration, but it also provides more durable pavements that are less susceptible to the effects of temperature. [ABSTRACT FROM AUTHOR]

Although rubberized asphalt has more than a 50-year history, it has not been widely adopted due to difficulties with its processability, unstable properties and high initial cost. Chemical approaches, including chemical characterization and the addition of chemical additives to rubberized asphalt, are useful tools to promote the applications of this technology. Chemical characterization techniques such as infrared spectroscopy, thermogravimetric analysis, gel permeation chromatography, and sol-gel analysis are used to analyze the chemical composition of rubberized asphalt. The development of chemical characterization for rubberized asphalt is described in terms of chemical degradation of rubber in asphalt, and stabilization of rubber in asphalt. The evolution of the chemical composition of rubberized asphalt has been evaluated and correlated for dry and wet processing, and indoor and outdoor aging. Following this, high performance rubberized asphalt realized by modification with different chemical additives is also discussed. The additives are categorized into polymers, inorganic filler, plasticizer and others. Finally, methods that combine several types of different additives that can be used to produce rubberized asphalt with stable properties and in an environmentally friendly manner are described. [ABSTRACT FROM AUTHOR]