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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.

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.

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.

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.

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.

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.