A review of thermal processes in the production and their influences on performance of asphalt mixtures with reclaimed asphalt pavement (RAP)

The use of reclaimed asphalt pavement (RAP) in asphalt mixtures is considered as one of the best sustainable practices in the construction of transportation infrastructures. Extensive efforts have been made to design, produce, and evaluate RAP mixtures produced by the hot recycling technology in asphalt plants. However, the inconsistencies or contradictive conclusions regarding the performance of RAP mixtures reported in the literature impede the use of high percentage of RAP in asphalt mixtures. One of the knowledge gaps for the discrepant behaviors of RAP mixtures is the negligence of the influence of production thermal processes, e.g. mixing time, production temperature, silo storage temperature and time, etc., on the mechanical performance of RAP mixtures. In this context, this paper synthetically reviewed the fundamental thermodynamics and kinematics involved in the plant production of RAP mixtures and the corresponding numerical methodologies to quantify the thermal processes. Three prevailing numerical methods, including overall energy balance method, 1-D thermal-granular model, and coupled computational fluid dynamics and discrete element method, are used to quantify the temperatures of hot gases, virgin aggregates, and RAP particles in the drum dryer. Then, the key production parameters that could influence the performance of RAP mixtures were identified based on the experimental studies. The review results from the experimental studies highlighted the importance of mixing time, mixture discharge temperature, and silo storage time on the mechanical performances of laboratory-produced and plant-produced RAP mixtures. The review findings from this study can be used to guide the best practice of the production of RAP mixtures and further contribute to the energy saving and sustainable construction of using RAP in asphalt mixtures. (C) 2019 Elsevier Ltd. All rights reserved.