Multi-scale characterisation of composite crumb rubber–nano silica modified porous asphalt for improved functional performance

Porous asphalt concrete (PAC) provides effective surface drainage but remains susceptible to raveling, cracking, and moisture–induced deterioration due to its highly open structure. This study investigated whether the combined incorporation of crumb rubber (CR) and nano silica (NS) could improve PAC durability while maintaining drainage performance. A multi–scale experimental program was conducted using CR (0–10%) and NS (0–6%) at both binder and mixture levels. Fourier transform infrared spectroscopy (FTIR) showed that NS enhanced network densification through intensified Si–O–Si vibrational features, whereas CR exhibited minimal spectral changes, indicating physical swelling rather than chemical bonding. These interaction mechanisms were reflected in the performance results. Multiple stress creep recovery (MSCR) testing showed a reduction of more than 40% in non–recoverable creep compliance, indicating improved rutting resistance. NS increased Marshall stability by up to 22.9%, while CR more effectively reduced abrasion, lowering Cantabro loss by approximately 9%. However, NS contents above 4% reduced permeability and accelerated clogging, indicating a trade–off between durability and drainage performance.