Rheological and microstructural investigation of sodium-based montmorillonite nanoclay modified bitumen at mastic scale

The present study investigates the impact of organo-modified nanoclay (OMNC) on the rheological and microstructural properties of bitumen mastic. Different bitumen blends of OMNC ranging between 0% and 8% with 2% incremental steps by weight of the bitumen were prepared with a constant filler to bitumen ratio of 0.8 using a high shear mixer (HSM). The samples were investigated for unaged and short-term aged conditions. High-temperature performance grade (PG), frequency sweep, and multiple stress creep and recovery (MSCR) tests were performed on unaged and rolling thin film oven (RTFO) aged mastics to characterise the high-temperature performance properties. The master curve analysis revealed that OMNC significantly improves the rutting performance of mastic at both intermediate and higher temperatures. Significant improvement in the Superpave rutting parameter (G*/sinδ), recovery percentage (%R), non-recoverable creep compliance (Jnr), zero shear viscosity (ZSV), and elastic modification index (Em) was achieved, proving the efficacy of OMNC in enhancing the rutting performance of the mastic. Moreover, under unaged conditions, the samples reached the failure criterion of PG grading at 82ºC, 82ºC, 88ºC, and 94ºC for the 2%, 4%, 6%, and 8% OMNC dosages, respectively, compared to 70ºC for the controlled mastic without OMNC. Scanning electron microscope (SEM) analysis was performed for morphological assessment. Proper dispersion was seen through SEM. Finally, Fourier transform infrared (FTIR) spectroscopy was used to investigate the chemistry between the bitumen and OMNC. Delay in mastic ageing was observed from the sulphoxide and carbonyl indices with the addition of OMNC.