Role of thermodynamic relaxation on effectiveness of recycling agents on properties of aged bitumen

• Published in: Fuel (Guildford) 2024-07, Vol.368, p.131658, Article 131658
• Main Authors: Ren, Shisong, Liu, Xueyan, Erkens, Sandra
• Format: Article
• Language: English
• Subjects: Low-temperature performance; Molecular dynamic simulation; Multi-scale connection; Rejuvenated bitumen; Thermodynamic indicator
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2024.131658

Note: τ50s-shear stress at 50s, t25%-relaxation time at 25% residue stress, A-relaxation model parameter, FFT-fatigue failure temperature, Nf5-fatigue life with 5% strain, E-elastic modulus, C500-crack width at 500 cycles, FFV-fractional free volume, MSD-mean square displacement, Ds-self-diffusion coefficient, Tg-glass transition temperature, γ-surface free energy, Waa-work of cohesion. [Display omitted] •(1) A multi-scale evaluation framework on low-temperature relaxation and fatigue performance of rejuvenated bitumen was developed.•(2) Synthetic effects of recycling agent type/dosage and aging degree of bitumen were studied.•(3) Effective thermodynamic parameters of rejuvenated bitumen were proposed.•(4) Potential connections between molecular-level indices with critical relaxation and fatigue performance indicators were explored. The low-temperature relaxation and fatigue cracking performance are two essential aspects in estimating the rejuvenation efficiency of recycling agents (RAs). This study aims to fundamentally investigate the effects of recycling agent type/dosage and aging degree of bitumen on thermodynamic and rheological properties of rejuvenated bitumen at low and intermediate temperatures. Molecular dynamics (MD) simulations are utilized to predict thermodynamic indices of rejuvenated bitumen, further linked to critical low-temperature and fatigue indicators from experiments. The results reveal that all RAs show a regeneration effect on fractional free volume (FFV), self-diffusion coefficient (DS), glass transition temperature (Tg), and surface free energy (γ). Bio-oil and engine-oil exhibit higher rejuvenation efficiency on these thermodynamic properties than naphthenic-oil and aromatic-oil. The aging degree of bitumen and temperature show significant effects on rejuvenation efficiency. It is recommended to use the FFV parameter to predict the relaxation properties of rejuvenated bitumen. However, these thermodynamic indicators inadequately differentiate between rejuvenators and softeners. Based on crossover parameter results, most recycling agents (bio-oil, engine oil, and naphthenic oil) in this study display softening characteristics. Only aromatic oil effectively rejuvenates the crossover modulus (Gc) of aged binder. Notably, engine oil demonstrates the least rejuvenation in crossover parameters for the recovery of aged bitumen. Further, γ demonstrates a strong association with both Glover-Rowe (G-R) and fatigue crack width C500 indice