Influence of Recycled Asphalt Pavement Material Dosage on the Dynamic Modulus of Hot-Recycled Bituminous Mixtures Using Design of Experiments Approach

This study develops a statistics-based design of experiments (DoE) framework to optimize recycled asphalt pavement (RAP) proportions for achieving targeted binder properties and dynamic modulus characteristics of the mixture. Using three distinct recycled binder formulations—varying in RAP binder, virgin binder, and rejuvenator content— the influence of RAP dosage on mechanical response across a range of temperatures and frequencies is documented. RAP mixtures containing 16%, 23%, and 28% RAP are prepared alongside a control mixture, with all mixtures maintaining a bituminous concrete (BC) Grade II midpoint gradation and an overall binder content of 5.4%. All the samples are subjected to repeated haversine compression loading for a range of frequencies (0.01 to 25 Hz) and temperatures (5°C to 55°C). At lower temperatures (up to 15°C), the overall stiffness of the mixtures dominates the mechanical response, minimizing the influence of RAP binder stiffness. At higher RAP contents (23% and 28%) and elevated temperatures (55°C), notable differences are observed in dynamic modulus and phase angle trends. Master curve modeling and continuous relaxation spectra were used to quantify the differences between binder-level and mixture-level studies and to identify specific temperature-frequency regions where these discrepancies emerged. Up to 16% RAP content, the expected similarity between binder and mixture responses was observed. However, at higher RAP contents (RAPM 23% and RAPM 28%), significant differences in dynamic modulus were detected across different frequencies, highlighting the influence of RAP incorporation on mixture behavior.