Coupling Microwave Treatment and NaClO Oxidation for Excellent Compatibility of Crumb Rubber and Asphalt: Methods and Mechanism

Crumb rubber (CR) modified asphalt facilitated waste tire recycling, but poor CR-asphalt compatibility limited high CR dosage. Accordingly, microwave-assisted NaClO-oxidized CR (MOCR) was prepared, with optimal conditions obtained by single-factor and orthogonal experiments. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), contact angle (CA) measurement, X-ray energy-dispersive spectroscopy (EDS), and thermogravimetric analysis (TGA) were employed to investigate the effect of coupling oxidation treatment on CR. It was found that after the combined oxidation, disulfide bonds (-S-S-) and polysulfide bonds (-Sn-) were cleaved, producing sulfone (-SO2-) and sulfoxide (-SO-) functional groups. Furthermore, DFT calculations verified that the oxidized CR possessed excellent compatibility with base asphalt (BA). Softening point difference (SPD), segregation index (SI), and fluorescence microscopy (FM) results confirmed that MOCR-modified asphalt (MOCRMA) exhibited optimal storage stability. Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests demonstrated that MOCRMA exhibited superior high- and low-temperature rheological performance.