Effects of degree of devulcanization on the compatibility and rheological properties of ground tire rubber-modified asphalt

Recycling waste rubber to produce rubber-modified asphalt is a promising way for sustainable material reuse while enhancing pavement performance. However, poor storage stability caused by the separation of rubber and asphalt remains a significant challenge. The devulcanization process, which partially changes the chemical structure of rubber, presents a solution to these compatibility issues. This study employed a thermal–mechanical process (using a twin-screw extruder with controlled shear strain and temperature) to partially devulcanize ground tire rubber (GTR) at different temperatures (240 °C, 260 °C, 280 °C), characterized the microstructural properties of the devulcanized GTR, and evaluated the performance of the rubber-modified asphalt. The objective is to quantify the relationship between rubber devulcanization and the production of high-performance rubber-modified asphalt. Fourier transform infrared (FT-IR) spectroscopy was used to analyze the chemical changes occurring during devulcanization. After preparing GTR modified asphalt samples under controlled temperature and shearing rate, the storage stability and basic properties of the modified asphalt were assessed using separation tests, rotational viscosity (RV) measurements, dynamic shear rheology (DSR), and bending beam rheometer (BBR) tests. The results indicated that storage stability improved, with Separation Index dropping from over 40 % (untreated) to below 10 % at 260–280 °C for 12 % and 18 % GTR. Viscosity at 165 °C decreased by up to 50 %, enhancing workability. However, rutting factor | G *|/sin δ at 64 °C decreased from 25.7 kPa (untreated, 24 % GTR) to 3.7 kPa (280 °C devulcanized), reducing high-temperature resistance. While devulcanization reduces the elasticity of rubber—simplifying the mixing and application process—it can compromise high-temperature performance due to increased deformation under high temperatures. Optimizing the control of devulcanization temperature and rubber content can help balance the asphalt binder’s performance and stability. These findings provide valuable insights into the GTR devulcanization process and support the development of more efficient and cleaner production techniques for rubber-modified asphalt, thereby broadening its potential applications in pavement engineering.