Utilization of high contents of recycled tire crumb rubber in developing a modified-asphalt-rubber binder for road applications

Waste tires are generally mixed with asphalt materials to produce asphalt-rubber (AR) or rubberized asphalt through wet-, dry-, and terminal blending processes. However, the limitations such as long-term storage and stability issues of these special products have led to the need for advancing the AR technology capable of mitigating the production-related problems. Thus, the major objective of this research was to re-engineer AR in the form of a set of eighteen modified-asphalt-rubber (MAR) products comprising high contents of recycled tire crumb rubber (CR) through activation and pulverization. A set of MAR products was synthesized through different blending dosages, sequences, and material combinations. The material characterization techniques (attenuated total reflection-infrared spectroscopy and powder X-ray diffraction) revealed that the type of additives and the proportions of each material pose a significant effect on the physiochemical properties of MAR. It is noteworthy that this study emphasized the best use of CR emanating out of scrap tires in paving applications through incorporation of higher volumes (as large as 62%) in the preparation of MAR when compared to the conventional AR binder that currently includes about 15–20% CR by weight of the base asphalt binder. The fatigue performance of MAR-modified dense graded mix (MAR blended with natural aggregates) was compared to the conventional mix, which revealed that the MAR-modified dense graded product will have higher fatigue life by more than two times, and increased durability than the conventional mix. Practically, the MAR products can be used for instant application in pothole patching, rehabilitation, and new construction through dry-process technology by replacing a reasonable proportion of conventional aggregates in the asphalt mix. It is envisioned that the MAR binders will reduce the overall cost of pavement construction by utilizing the untreated (or unprocessed) CR in larger quantities by actively supporting the recycling mechanism and circular economy.