Understanding the Effectiveness of Microwave Irradiation Based Approach for Improving the High Temperature Storage Stability of Crumb Rubber Modified Asphalt Binder

High temperature storage stability (HTSS) is one of the major bottlenecks for the widespread application of rubberized asphalt. To overcome this, various surface activation techniques have been explored in the literature. Among them, microwave (MW) irradiation has emerged as a promising approach because of its potential effectiveness for lab-to-field implementation. However, whether it adequately addresses HTSS-related challenges to ensure consistent binder performance remains unclear and requires detailed investigation. This study presents a detailed assessment on the effectiveness of MW-based activation in improving the HTSS of crumb rubber (CR)-modified asphalt from a performance based parameter perspective. To achieve this, CRs were activated with different MW specific energies (0–6 kJ/g), and the resulting changes in their properties were investigated using various experimental techniques [scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA)]. The influence of MWs on the HTSS of rubberized binders with 10% and 20% CR (by binder weight) was initially evaluated using the conventional softening point difference based approach. The effectiveness of MWs in producing consistent performance related rheological parameters, such as rutting and fatigue resistance, was further investigated. Finally, direct measurement of CR concentration at different parts of the separation tube revealed that MW irradiation does not effectively hold the promising ability to activate CR surfaces. This study suggests that MW is less effective in improving HTSS, particularly at lower CR content (10%) compared to CRMA with 20% CR. The softening point based approach was found unsuitable for HTSS evaluation. Further analysis revealed that MW surface activation does not sufficiently enhance the uniformity of rubberized asphalt properties from high as well as intermediate temperature performance perspectives, which is further supported by direct measurements of CR concentration within the binder. Therefore, it is fair to infer that MW irradiation alone should not be solely relied upon to address the HTSS problem.