Temperature and contact states of hot-recycled asphalt mixing at a non-thermal equilibrium condition based on discrete element method

Abstract

The mixing of hot recycled asphalt mixture (HRAM) plays a critical role in its performance, particularly in non-uniform temperature environments and high RAP content scenarios. Therefore, it is imperative to investigate the mixing process of HRAM to achieve high-quality production of HRAMs. In this study, the DEM method was employed to simulate the mixing process of HRAMs with predetermined RAP temperatures of 353 K, 373 K, and 393 K, and varying RAP contents at 20 %, 40 %, and 60 %. Statistical analysis of temperature distribution was conducted. Additionally, for representation of particle contact state, contact number statistics and coordination number indicators were introduced. The study revealed that with increasing mixing time, the temperature distribution of asphalt mixture particles gradually concentrated and the average temperature decreased. In all cases examined in this study, a turning point in the temperature field distribution was observed at approximately 50 seconds. Complete thermal equilibrium was not found in a limited mixing time of 90 seconds. The interaction between particles underwent significant changes during the initial stages of mixing and stabilized in the final state, which was influenced by both the RAP content and predetermined RAP temperatures. The ANN (Average Nearest Neighbour Analysis) index introduced can serve as a crucial indicator to characterize the mixing of hot-recycled asphalt mixtures.