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• 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]

• A biphasic random generated model was introduced to simulate microstructure of modified bitumen. • Using 2D or 3D heterogeneous viscoelastic FE models of the BBR test resulted in identical outputs. • Addition of crumb rubber having lower modulus than bitumen improved critical cracking temperature. This paper uses a heterogeneous micromechanical model to evaluate the resistance to thermal cracking in bituminous composites containing granular particulates. Thermal cracking is mainly caused by temperature fluctuations leading to accumulated stress that exceeds the strength of the materials. The presence of various granular particulates significantly affects a material's strength and capacity to release stress. Here, we use a two-dimensional heterogeneous numerical finite element model to evaluate and predict the thermal cracking characteristics of bitumen containing granular particulates such as crumb rubber and taconite. To develop the model, randomly distributed polygons using the Delaunay triangulation method were used to represent taconite and crumb rubber inside a bitumen matrix. The elastic properties of taconite and crumb rubber were assigned to the particulates, and the viscoelastic properties of the bitumen were modeled using a Prony series by implementing a simple fractional viscoelastic model. The study results showed that the flexural creep stiffness and creep rate calculated by the model were in good agreement with the measurements of experiments: the maximum errors were 6.15% for bitumen containing crumb rubber and 13.72% for bitumen containing taconite. Considering that flexural creep stiffness and creep rate are commonly used as indicators of thermal cracking resistance, the newly developed heterogeneous micromechanical model can be used to evaluate the thermal cracking resistance of bituminous matrices containing granular particulates. The model was further used to study the effects of temperature, elasticity, and concentration of particulates on the cracking resistance of the bituminous matrix. For instance, it was found that introducing 16% particulates with an elasticity of 1.02 MPa (representing crumb rubber) to bitumen improves its critical cracking temperature from −25 °C to −29.3 °C. This model provides insights to help the design of bituminous composites with desired cracking resistance properties by incorporating the proper particulates. [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]

• Measuring LVE properties of bituminous composites through a multiscale simulation. • Multiscale simulation has more accuracy than the generalized self-consistent scheme. • 3.35 mm is the best mortar cutting size to find mixture behavior with NMAS of 19 mm. Viscoelastic properties of asphalt mixture were studied through a multi-scale approach, including bitumen, mastic, mortar, and mixture length scale. Biphasic and triphasic finite element modeling were employed to construct the heterogeneous models of bituminous composites, including matrix, inclusions, and air voids. The 2S2P1D model consisting of two springs, two parabolic creep elements, and one dashpot was fitted on the output of the numerical model, i.e., dynamic modulus (E*) and phase angle (δ), to accurately determine the Prony series. Then, the data of each scale was utilized as a matrix for the next scale's model. Three cutting sizes, including 3.35, 2.36, and 1.7 mm were selected based on the previous experimental study of Khodadadi et al. (2021) to generate the mortar model and find the best length scale of the matrix. In addition, the numerical results were compared with the results of the generalized self-consistent scheme model as an analytical approach. Both numerical and the generalized self-consistent scheme models yield adequate results; nevertheless, the numerical solution has more accuracy than the analytical model. The cutting size of the mortar scale had a considerable effect on the LVE properties of the mixture. The result showed that a cutting size of 3.35 mm is more suitable for a mixture with a nominal maximum aggregate size of 19 mm. These findings were consistent with the experimental results. [ABSTRACT FROM AUTHOR]