A Comparative Study of Macro- and Microstructural Characteristics of Asphalt Mixtures Incorporating Crumb Rubber (CR) in Powder, Shredded, and Cube Forms

The disposal of used tires has created a considerable environmental problem, prompting the development of sustainable alternatives, such as incorporating crumb rubber (CR) into asphalt mixtures. This study aims to assess the effect of three CR forms, namely powder, shredded, and cubic, on the analysis of both the macro and microstructural properties of asphalt. Marshall samples were prepared with different forms of CR and subjected to a comparative study based on Marshall Stability and volumetric properties. Results indicate that CR-modified mixtures increase durability, deformation resistance, and thermal stability, with optimal CR contents showing improved Marshall Stability: 14.99 kN for 10% powder CR, 15.08 kN for 15% shredded CR, and 15.11 kN for 10% cubic CR. Enhanced softening point of up to 73.9 °C and lower penetration values indicate higher stiffness and crack resistance, while workability is retained within acceptable flow ranges. Scanning Electron Microscope images of the powder and shredded CR showed increased surface areas, facilitating interactions with the asphalt matrix and ultimately increasing stability. Energy Dispersive X-ray Spectroscopy analysis verified that hydrocarbons were the primary component of CR, and no chemical reaction between CR and asphalt constituents further confirmed only physical interaction. Research has addressed environmental problems and heavy traffic loads by recycling waste tires into economical and long-lasting materials. Moreover, additional research may conduct field trials to support validation and practical performance evaluation.