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The long-term aging of bitumens and its effect on low-temperature performance is a detrimental phenomenon. In order to investigate the effects of the aging phenomenon on the low-temperature performance of bitumens, it is very important to accurately simulate the behavior of bitumens in repeated aging cycles and to investigate related viscoelastic, chemical, and microstructural changes. In this research, three types of bitumen with penetration grades of 40/50 , 60/70 , and 85/100 were subjected to one to three cycles of pressure aging vessel (PAV) aging. Comprehensive data on the bitumen's behavior were obtained by conducting bending beam rheometer, Fourier transform infrared spectroscopy, and atomic force microscopy tests. Using the results of the conducted tests, an attempt was made to find precise relationships between different indicators of bitumen aging in terms of chemistry and viscoelasticity. The results revealed a linear correlation between the aging index and the ΔTc and dissipated energy ratio (DER) values, as well as the aging index and the vertical shift factor of the stiffness-time curve. The fitting coefficients of these linear relationships were R2=0.8 and above, indicating a strong linear relationship between these parameters. Furthermore, the viscoelastic indices DER and the derivation of creep compliance (J′) exhibited a fairly good linear relationship. [ABSTRACT FROM AUTHOR]

The objective of this study is to create explicit prediction models for the complex shear modulus (G*) and phase angle (δ) of bitumen mastic fabricated using an evolutionary machine learning approach. The dynamic shear rheometer (DSR) test in frequency sweep mode at seven test temperatures was performed to measure G* and δ. In order to create specific prediction models for each modifier, multigene genetic programming (MGGP) was employed. These models took into account various factors including the dosage of the additive, filler volume filling rate, loading frequency, temperature, as well as the G* and δ values of the neat bitumen. In general, six explicit prediction models are presented for different additives with R-squared values of more than 0.9. The results showed that the hybrid machine learning approach can effectively develop precise, meaningful, and yet simple formulas for calculating G* and δ of the bitumen mastic. To gain a deeper understanding of the developed models, a comprehensive parametric study and sensitivity analysis were carried out. [ABSTRACT FROM AUTHOR]

In this study, the mutual effect of polyphosphoric acid (PPA) and ethylene bis(stearamide) (EBS) modification was examined on the high and low service temperatures and viscosity of a performance grade (PG) 58-22 asphalt binder as a conventional neat bitumen widely used for paving applications. Three different dosages of PPA, including 0.5%, 1.0%, and 1.5% were used to modify the neat asphalt binder, and 3% of EBS as a selected percentage was added to PPA-modified samples. The dynamic shear rheometer was used to evaluate the high-temperature properties of the neat and modified bitumens based on standard Superpave protocol parameter (G*/sinδ) and multiple stress creep and recovery test. The low service temperatures of the samples were determined using the bending beam rheometer test. Also, the high-temperature ranges viscosities of the samples were evaluated using a series of rotational viscometer tests. The results have shown that increasing the PPA dosage up to 1.5% enhances the high service temperature of the neat asphalt binder 20.4°C and 14.7°C based on Superpave protocol and multiple stress creep and recovery test, respectively. However, it deteriorates the low-temperature performance of modified binders from −24.3°C to −16.9°C. The EBS can significantly compensate for the negative effect of PPA modification on the low-temperature behavior of modified bitumens. The optimum combination was 1% PPA+3% EBS as it provides a similar low-temperature grade to the neat asphalt binder having a significant two grades enhancement of high service temperature. Modifying a PPA-modified asphalt binder with EBS can reduce its viscosity at high temperatures, leading to saving energy of mixing and compaction. [ABSTRACT FROM AUTHOR]