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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]

• Predicting J nr and %R of modified bitumens deterministically by using MGGP based on MSCR test results. • Predicting probability of different traffic levels by using logistic regression technique. • Determining the critical dosages of crumb rubber, SBS, and PPA modifiers that alter the traffic levels. This study aims to develop deterministic and probabilistic prediction models for the multiple stress creep and recovery (MSCR) test. For this purpose, crumb rubber, polyphosphoric acid, and styrene–butadiene–styrene bitumen modifiers have been used with different dosages to modify high-temperature performance of PG 58–28 and PG 64–22 base bitumens. The MSCR test has been performed at different temperatures. Deterministic models are developed by the multi-gene genetic programming technique for each modifier individually, and the non-recoverable creep compliance (J nr) and percent recovery (R) parameters are predicted. The accuracy of deterministic models is suitable and the performance of R models has been better than J nr models. Furthermore, a comprehensive probabilistic model has been developed by using the logistic regression technique to predict different traffic levels. The accuracy of the probabilistic model is 0.85. The sensitivity analysis has been performed on this model and the effect of changes in the modifier dosage and temperature on the traffic levels have been investigated. Results show that using the probabilistic model, it is possible to find a range of modifier's dosage in which the traffic level is desired. [ABSTRACT FROM AUTHOR]

[Display omitted] Introducing waste plastics in bituminous composites can increase the composites' durability, provided that the waste plastics are compatibilized with bitumen to avoid phase separation. To enhance the compatibility of plastic particles with bitumen, various treatment methods were used to alter their physical and chemical characteristics. Considering the complex nature of bitumen, knowing the properties of isolated particles is not sufficient to indicate their performance in a bituminous composite. Therefore, there is a need to quantify the efficacy of each treatment method directly. While the plastic-bitumen interface can be examined via advanced characterization instruments such as atomic force microscopy, those methods are often relatively complicated and time consuming for formulators and designers. Here, we use a heterogeneous micromechanical model to calculate compatibility indicators; the model is tailored for viscoelastic bituminous composites containing waste-plastic particles. With experiments using a dynamic shear rheometer and a bending beam rheometer, data were generated on the bitumen with and without waste plastics having various surface treatments. The model was then used to calculate the Effective Volume Filling (EVF) ratio to indicate the interaction between plastics and bitumen as a measure of compatibility. A higher EVF ratio indicates greater compatibility. The corresponding EVF ratio was found to be higher for the oil-treated plastics compared to non-treated plastics, demonstrating higher compatibility of the oil-treated plastics with bitumen. This study promotes sustainability in construction by facilitating the use of waste plastics and enhancing the cracking resistance of bitumen. [ABSTRACT FROM AUTHOR]

This study exploits silica and polyphosphoric acid (PPA) synergistic effects to produce air-blown bitumen with desired stiffness and reduced carbon footprint. This in turn enhances the durability of the resulting air-blown bitumen while reducing gaseous emissions associated with its production. Here, we hypothesize that PPA-grafted silica made by adsorption of polyphosphoric acid to pristine silica nanoparticles promotes intermolecular interactions in vacuum bottom (VB), facilitating the production of air-blown bitumen. To test this hypothesis, laboratory experiments and modeling were used to determine the underlying molecular interactions determining PPA-grafted silica's role in facilitating the production of air-blown bitumen. Our molecular modeling showed PPA promotes the interaction between VB molecules by up to 10.28%; this combined with the increased polarity of VB molecules during the air-blowing process, leads to a significant increase in intermolecular interactions accelerating VB's stiffening. The latter was evidenced in our experiments showing that the required air-blowing time to reach desired stiffness measured by penetration and softening point was reduced up to 25% (time to reach required stiffness was reduced from 120 min to 90 min when silica-grafted polyphosphoric acid was used). Reduction of manufacturing time reduces VB's exposure to heat which leads to the formation of secondary organic aerosols. This promotes the economic and environmental sustainability aspects of the air-blowing process and contributes to resource conservation. [Display omitted] [ABSTRACT FROM AUTHOR]

• Fractional viscoelastic model can characterize low-temperature mechanical behaviour of bio-modified bitumen. • Bio-modifiers effects on bitumen's properties is highly source dependent. • Bio-modifiers have positive effect on bitumen performance at low service temperatures. • Bio-modifiers enhance bitumen behaviour during both creep-loading and relaxation. Cracks associated with large temperature fluctuation especially in cold regions are among prevalent pavement distresses. Binder rheology is typically found to the key factor affecting low temperature cracking resistance. Recognizing the importance of binder properties, many road authorities are requiring the use of special additives to enhance low temperature properties of binder to alleviate low temperature cracking problems. However, most of these modifiers are petroleum-based products with unstable price and depleting resources. Therefore, the asphalt industry is looking for renewable alternatives for modifying bitumen and improving its low temperature performance. Accordingly, this paper incorporates laboratory experiments and modeling to study merits of modifying bitumen with several bio-binders to enhance low temperature properties of bitumen. To investigate rheological properties at low temperatures, an extended bending beam rheometer test was used incorporating a simple fractional viscoelastic model based on the general power law. The data collected during loading and unloading portion of the test was used to evaluate the effect of introduction of bio-modifiers on low temperature properties of bitumen. The experimental results showed that introduction of bio-modifiers to bitumen significantly enhanced bitumen behavior both during creep loading and relaxation. The results of finite element modeling based on the extended bending beam rheometer geometry and boundary conditions proved that the simple fractional viscoelastic model can accurately characterize low-temperature mechanical behavior of bio-modified bitumen. [ABSTRACT FROM AUTHOR]

• Performing temperature sweep test to generate master curves for viscoelastic properties of bitumen. • Optimizing the number of frequencies and temperatures to develop master curves of asphalt mortar and mixture. • Reducing the time and cost of dynamic modulus test without missing the accuracy of master curves. This study aimed to assess the feasibility of substituting temperature sweep tests for frequency sweep tests and explore the potential of utilizing fewer temperatures and frequencies in dynamic modulus tests to formulate viscoelastic properties master curves. The results indicated that master curves derived from temperature sweep tests mirrored the trends and values obtained from frequency sweep tests, presenting a viable alternative for constructing viscoelastic properties master curves of bitumen. Furthermore, models fitted to dynamic modulus test results at three temperatures and three frequencies exhibited comparable primary parameters, values, and trends to those derived from the complete dataset. The model fitted on reduced data demonstrated robust performance with correlation and R-squared values exceeding 0.95. Considering a marginal increase of about 5% in Residual Standard Error (RSE) values when using the reduced dataset, generating master curves with fewer test results underscored the feasibility and reliability of the original master curves. [ABSTRACT FROM AUTHOR]

• Using a multi-scale approach to find viscoelastic properties of three scales: mastic, mortar, and mixture. • Threshold stress is evaluated to characterize linear viscoelastic properties of the mortar scale. • Mortar with the cutting size of 3.35 mm has the closest behavior to the asphalt mixture with an NMAS of 19 mm. The mortar component plays an essential role in forming different asphalt mixture distresses. The fine aggregate size affects the viscoelastic behavior of mortar. In this study, three cutting sizes of 3.35, 2.36, and 1.7 mm, on the aggregate grading curve were considered to construct the mortar scales, namely mortar (I), (II), and (III), respectively. With a unique loading mode, a frequency sweep test was performed on four different length scales, including bitumen, asphalt mastic, mortar, and asphalt mixture, to make a direct comparison through a multi-scale approach. Also, a stress sweep test was conducted to find the mortar scale's linear viscoelastic domain. The results indicate that different mortar types have variable linear viscoelastic domains. The master curves of dynamic modulus (E*) and phase angle (δ) show that adding filler to bitumen has more effect on the E* than the δ. Although scaling up from the mastic to mortar (II) causes a significant difference between the viscoelastic parameters, the results remained approximately the same. The main gap between the mixture and mentioned sub-scales is filled with mortar (I). While the Cole-Cole diagrams demonstrate that the bitumen to mortar (II) scales have the same behavior, the closest scale to the mixture is the mortar (I). Therefore, using a cutting size of 3.35 mm is recommended to fabricate mortar (for asphalt mixture with a nominal maximum aggregate size of 19 mm) instead of 2.36 mm, which was suggested in previous studies. [ABSTRACT FROM AUTHOR]