Effects of recycled asphalt shingle on the rheological and molecular composition properties of asphalt cement

Recycling of asphalt shingles in flexible pavements has received interests in recent years due to economic, environmental, and social reasons. The objective of this study is to introduce a new approach to recycle asphalt shingles in asphalt paving construction in which RAS is ground to ultra-fine sizes and blended with asphalt binder through a wet process. In this method, the ground recycled material is blended with the binder at high temperature prior to mixing with the aggregates. Two unmodified binders that are classified as PG64-22 and PG52-28 were blended with two contrasting sources of RAS, originating from tear-off and manufacturer wastes, at a modification content ranging from 10 to 40% by weight of the binder. The use of RAS modification through the proposed wet process was successful. The use of RAS modification through the proposed wet process would generally improve or not influence the high temperature grade of the binder but it may reduce the low temperature grade of the binder. An optimum shingle content may be identified that will improve the high temperature grade without influencing the low temperature grade of the binder. Using Confocal Laser-Scanning Microscopy, wax crystals were detected. However, wax crystals were not detected in the RAS-modified binder, which may indicate that the wax molecules are absorbed by the RAS material. Results of HP-GPC showed that the proposed wet method of modification caused a slight increase of the High Molecular Weight (HMW) content in the prepared blends especially at high content of RAS modification. Use of RAS resulted in an increase in viscosity ranging from 3 to 130%. The increase in viscosity was proportional to the RAS content with greater increase at RAS content of 30% and in blends prepared with RAS from tear-off. The temperature susceptibility of the binder in the range from 95 to 135°C decreased with the use of RAS. Thixotropy and shear thinning were observed concurrently in the asphalt binder blends at 25°C. In addition, RAS-modified asphalt binders showed greater susceptibility to thixotropy than the base binder. Thixotropy increased with higher RAS content