Rheological Properties and Performance of Geopolymer-Modified Crumb Rubber–Modified Bitumen at High Temperatures

In developing countries like India, the rise in traffic plays a pivotal role in the deterioration of flexible pavements. Modified binders have gained popularity due to their significant structural potential. However, modified binders are more implicated in the release of detrimental pollutants and necessitate elevated temperatures during the manufacturing procedure. In this study, geopolymers are materials synthesized from an industrial waste product (Class F fly ash) combined with 10 M sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) as an alkaline medium produced at 40°C. The study aimed to investigate the effects of geopolymers on the conventional and rheological properties of unaged crumb rubber–modified binder samples (CRMB-55) with varying proportions of geopolymers (0%, 4%, 6%, 8%, and 10%) at high temperatures. The assessment of the softening point, penetration, elastic recovery, and viscosity of bitumen containing different levels of geopolymer components through conventional bitumen experiments were performed. Materials’ rheological properties were analyzed using dynamic shear rheometer (DSR) and multiple stress creep recovery (MSCR) tests. The findings suggest the addition of geopolymer modifies the rheological properties of the unaged asphalt binder. This was achieved by elevating its viscosity, complex shear modulus, rutting resistance parameter, and failure temperature. An improvement in MSCR parameters was also observed, namely a reduction in the Jnr value and an elevation in the R%, when geopolymer was added to CRMB. However, geopolymer-modified binder, with a concentration of 10%, failed to fulfill the Superpave viscosity standard of 3 Pa·s at 135°C. The Fourier transform infrared spectroscopy (FTIR) study indicated that the addition of geopolymer to the binder did not result in any alteration of the functional groups, reflecting unchanged chemical structure. Hence, it can be deduced that the geopolymer-modified binder with 8% concentration is the most favorable option in terms of performance.