The effect of the silo-storage on the rheological behavior of a surface course asphalt mix containing Reclaimed Asphalt Pavement (RAP)

The extent of diffusion/blending between aged binder from reclaimed asphalt pavement (RAP) and virgin binder in asphalt mixtures could affect both the performance of the produced Hot Mix Asphalt (HMA) and the economic competitiveness of the recycling process. During the production process of HMA with RAP, it is generally understood that a partial blending occurs between aged and virgin binders. The degree of blending could be increased, and the blending could be reached to completion by increasing the time of silo storage after the mixing. Nevertheless, a limited number of studies have considered the time-temperature effects of the silo storage on the diffusion mechanism between virgin and RAP binders. In this paper, the kinetics of blending of aged and virgin binders are examined by considering the time-temperature effect of silo storage on the rheological properties of HMA containing RAP. HMA samples of an HL-3 mix designed with 15% RAP were collected after production from the asphalt plant at different silo-storage intervals (1,4,8, and 12 hours), with their temperature being closely monitored and recorded. The resulting mixes were compacted on-site, and their rheological properties were characterised using the Complex Modulus Test. The analysis of these results indicates that there is no significant change in the stiffness of the mixes in the silo storage time varied from 0 to 1 and 4 hours. Yet, there is a noticeable change in the rheology of the mix for 8 hours and 12 hours at the test temperatures above 4°C. This change is directly associated with higher temperature and low frequencies of the complex modulus test. Therefore, silo storage time had an impact on the rheological behaviour at higher temperature and low frequencies during the test, which indicated a better blending of aged and virgin binders with higher storage time.