Rheology and Aging Resistance of Asphalt Modified with Calcined Kaolin

This study aimed to explore the potential of calcined kaolin (CK) as an asphalt modifier. CK at 5%, 10%, 15%, and 20% by asphalt weight was blended in asphalt binder at a high temperature, followed by aging treatments using a rolling thin film oven (RTFOT) and a pressure aging vessel (PAV). Changes in rutting, fatigue, temperature susceptibility, and aging resistance of the modified asphalt were tracked. The composition and structure of CK were analyzed using X-ray diffraction (XRD) and backscattered electron imaging-particle size (BSD-PS). Rheological studies of the modified asphalt were conducted using rotational viscosity, frequency sweep, multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) tests. The effects of CK on bitumen after thermo-oxidative aging performance decay were evaluated using aging indexes of physical indicators, complex modulus, and the phase angle. With the addition of CK, significant enhancement to stiffness was observed in the low- to mid-frequency range in the asphalt master curves, indicating that the impact of CK was mainly within the medium- to high-temperature range. The MSCR test results showed that the Jnr3.2 value for CK-modified asphalt accounts for 62% to 71% of virgin asphalt, indicating high rutting performance. The Cole-Cole diagram revealed different degrees of slope deviation toward the storage modulus axis for the storage and loss modulus curves after adding CK, suggesting an improvement in the asphalt's elastic properties. The CK asphalt binder exhibited higher R-values (152% to 181% of the virgin asphalt for R0.1 in the MSCR test) and fatigue cycle times (118% to 155% of the virgin asphalt for Nf in the LAS test) than those of virgin asphalt. Aging indexes and the Fourier-transform infrared spectroscopy (FTIR) test results indicated that CK can delay oxygen diffusion and the volatilization of lighter components. In conclusion, the results demonstrate that CK can effectively serve as a modifier to improve the mechanical and aging properties of asphalt binders.