Evaluation of Reclaimed Asphalt Pavement Binder Rejuvenating Behavior during Hot In-Place Recycling

In this paper, a micro-macro evaluation method of rejuvenator diffusion extent into aged asphalt in hot in-place recycling was put forward considering the cooling process of the recycled layer after paving. The material parameters were back-calculated by the backward regression method, and the temperature field of the recycled layer after paving was obtained by finite-element simulation and verified by the onsite measured data. The time-domain inverse method of the temperature field was proposed to exert the cooling process in a laboratory diffusion experiment of the rejuvenator. The macroviscosity index and micro-fourier transform infrared reflection-attenuated total reflection (FTIR-ATR) spectrum of aged asphalt before and after rejuvenator diffusion were compared, and the rejuvenator diffusion extents on the surface and inside the recycled asphalt layer in hot in-place recycling were studied. It was shown that the thermophysical parameters of recycling and original asphalt mixtures have an obvious influence on the cooling process of the recycled layer, which influence the rejuvenator diffusion process. Considering the actual temperature field of the hot in-place recycled layer is necessary, and the rejuvenator diffusion extent obtained from macro-micro methods showed high consistency. The unevenness of rejuvenator diffusion on the surface and inner recycled layer can be caused by their different cooling processes after paving, and it needs a long period to be eliminated in the environment temperature, which could bring nonuniformity to the properties of recycled mixtures. Increasing the mixing time of recycled mixtures appropriately and changing the thermophysical parameters of recycled mixtures to extend the cooling process are the keys to promote the diffusion of rejuvenator into aged asphalt.

Automated summary

This paper proposes a micro-macro evaluation method for the diffusion of rejuvenator into aged asphalt in hot in-place recycling, considering the cooling process of the recycled layer after paving. The material parameters are calculated using the backward regression method, and the temperature field of the recycled layer is obtained through finite-element simulation. The cooling process is incorporated into a laboratory diffusion experiment using the time-domain inverse method. The study finds that the thermophysical parameters of the recycled and original asphalt mixtures have a significant influence on the cooling process and rejuvenator diffusion. The nonuniformity of the diffusion on the surface and inside the recycled layer can be eliminated over time.