Laboratory evaluation of asphalt mixtures with reclaimed asphalt shingle prepared using the wet process

The objective of this study is to conduct a laboratory evaluation of asphalt mixtures containing recycled asphalt shingles (RAS) prepared using the newly developed wet process. In the proposed wet process, the 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 of the binder blend, to stimulate chemical and physical interactions taking place in the blend between asphalt cement (AC) in shingles and virgin AC in the mix, and to reduce maintenance issues at the plant due to the high content of fines and fibres in RAS. To achieve this objective, AC blends were prepared using the wet process and an asphalt mixture with a nominal maximum aggregate size of 12.5 mm was designed according to the Superpave design protocol. The mechanistic properties of asphalt mixtures containing RAS materials were evaluated as compared to conventional asphalt mixtures. Laboratory testing evaluated the rutting performance, fracture performance, and low-temperature resistance of the produced mixtures using the Hamburg Loaded-Wheel Tester, the Semi-Circular Bending test, and the Thermal Stress Restrained Specimen Test. Based on the results of the experimental programme, it was determined that the use of RAS through the wet process allows the reduction of the virgin binder content with no adverse effects on the laboratory performance of the mixture as compared to the conventional mixture with no RAS. Results also indicated that the blending of RAS directly with its regular processed size at the recycling plant with no additional processing in the wet process is feasible with no foreseen adverse effects on the mixture performance. However, it is recommended that the RAS be processed to the finest processing size possible at the recycling facility to stimulate chemical and physical interactions between recycled and virgin materials. Based on these results, additional work is needed to simulate plant operations using the newly developed wet process. Furthermore, research is needed on the shingle AC availability factor and its variation for the dry and wet recycling processes.