Improving durability of asphalt mixes with (RAP) by enhancing binder blending
Seminar with Hassan Baaj - Associate Professor, Norman W. McLeod Associate Chair at University of Waterloo and Director of the Centre for Pavement & Transportation Technology (CPATT).
Reclaimed Asphalt Pavement (RAP) has been favoured over virgin materials in the light of the unstable cost of virgin asphalt binders, shortage of quality aggregates, and compelling need to preserve the environment and natural resources. Mixes containing up to 20% RAP are commonly considered to have similar behaviour to virgin mixes. However, during the production process of HMA with RAP, the blending between aged and virgin binders would be partial, which would create heterogeneity in the distribution of the aged recycled binder and the virgin binder in the HMA-RAP mixes. Hence, it is important to control the blending process between old and new binders to obtain more homogenous mix. Therefore, the main objectives of this research were to examine the kinematics of blending of aged and virgin binders by considering the time-temperature effect during mixing and silo-storage, and assess the thermo-mechanical behaviour of Hot Mix Asphalt (HMA) containing RAP at different blending states. The asphalt mixes used in this research were produced and collected at two asphalt plants located in Ontario, Canada. The four mixes were produced with 15 to 40% of RAP and were conserved in silos for up to 24 hours with the objective to give more time to aged and virgin asphalt binders to blend. The mixes were tested in the lab using different classical binder and mix tests in addition to using Environmental Scanning Electron Microscope (ESEM) to evaluate the microstructure of original and blended binders. Moreover, the MEPDG AASHTOWare Pavement Mechanistic-Empirical Design was utilized to examine the effect of the 12-hour silo-storage time on the long-term performance of the pavements. The collected experimental evidences unveiled correlations between time-temperature effects and mixture performance. Based on these findings, the research provided practical recommendations to the professionals of the Canadian asphalt industry, that would applicable in different countries, for a better use of RAP. Ultimately, this research recommends a 12-hour silo-storage time for the RAP-HMA for better performance and durability of the mixes.
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