Master of Science in Civil Engineering (MSCE)


Civil and Environmental Engineering

Document Type



The objective of this study is to conduct a laboratory evaluation of asphalt mixtures and binders containing RAS prepared using the newly-developed wet process. In the proposed wet process, RAS material is blended with the binder at high temperature prior to mixing with the aggregates. The proposed wet process offers the potential to better control the Superpave Performance Grade (PG) of the binder blend, to stimulate chemical and physical interactions taking place in the blend between asphalt binder in shingles and virgin asphalt binder in the mix, and to reduce maintenance issues at the plant due to the high content of fines and fibers in RAS. To achieve this objective, asphalt binder blends with 10%, 20%, and 30% RAS were prepared using the wet process, and asphalt mixtures with a nominal maximum aggregate size (NMAS) of 12.5mm were designed according to the Superpave design protocol. The mechanistic performance of asphalt mixtures containing RAS materials was evaluated as compared to conventional asphalt mixtures. Laboratory mixture testing evaluated the rutting performance, fracture performance, and low temperature resistance of the produced mixtures using the Hamburg Loaded-Wheel Tester (LWT), the Semi-Circular Bending (SCB) test, and the Thermal Stress Restrained Specimen Test (TSRST). Results from the experimental program indicated that the proposed wet blending process allows a reduction of the virgin binder content with no detrimental effects on the laboratory performance of the mixture as compared to the conventional mixture without RAS. In addition, results suggested that the usage of RAS in its regular processed size, as processed by the recycling plant, is feasible with no foreseen adverse effects on the mixture performance. The resistance of the binder blends with RAS to fatigue and permanent deformation was evaluated through the use of the newly developed Linear Amplitude Sweep (LAS) test and the Multiple Stress Creep Compliance (MSCR) test. The effect of using different RAS amounts, as well as binder with two different PG grades, was investigated. Results of the LAS test showed that an increase in RAS leads to an increase in the number of cycles to fatigue failure. This is the opposite of what would be expected. These results indicate that the LAS test may not be suitable for characterizing RAS-modified asphalt binders. With respect to permanent deformation, it was found that the addition of RAS improved the performance of the blends by reducing the non-recoverable creep compliance and increasing elastic recovery.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Elseifi, Mostafa.