Storage Stability of Waste Tire Pyrolytic Char–Modified Asphalt Binders: Rheological and Chemical Characterization

Abstract

Pyrolysis is being employed as a viable option for the disposal of different industrial and agricultural wastes, including end-of-life vehicle tires. Tire pyrolytic char (TPC), a solid fine carbonaceous material obtained as a by-product during the pyrolysis of waste tires, is gaining interest among pavement researchers for its use in asphalt binder modification. Good storage stability is essential to ensure that a modified binder retains the desired properties after its fabrication. Cross-linking agents are frequently used to enhance the storage stability of modified binders. This study characterized the storage stability performance of TPC-modified binders with and without the incorporation of cross-linking agents. Bituminous binders modified with TPC were analyzed for storage stability at multiple dosages of two widely used cross-linking agents: polyphosphoric acid (PPA) (0.5%, 1.0%, and 1.5%) and sulfur (0.15%, 0.3%, and 0.45%). In addition to softening point difference (SPD), separation indices (SIs) derived from frequency sweep, temperature sweep, and multiple stress creep and recovery (MSCR) tests were employed to characterize the storage stability. Compatibility evaluation was also done through Cole-Cole plots. Fourier transform infrared spectroscopy (FTIR) was used to study the storage stability through the changes in binder spectra. Remixing of the TPC-modified binders was also performed to assess the retrieval of homogeneity in a segregated TPC-modified binder. All the SIs were measured and compared for binder specimens before and after remixing. Binders were ranked based on the SIs, followed by sensitivity and correlation analyses of the SIs. TPC-modified binder showed a good storage stability performance with sulfur (at 0.3% optimum dosage) and PPA (at 1% optimum dosage). Remixing resulted in further enhancement in the storage stability performance of TPC-modified binders. The results of the study are quite useful considering the practical usage of TPC for a storage-stable modification of asphalt binder.