Numerical investigation on phase separation in polymer-modified bitumen: effect of thermal condition

Abstract

With the aim to understand the effect of thermal condition on phase separation in polymer-modified bitumen (PMB), this paper numerically investigates four PMB binders under five thermal conditions between 140 and 180°C. Based on a phase-field model previously developed by the authors for PMB phase separation, the updated model presented in this paper uses temperature-dependent parameters in order to approach the concerned temperature range, including mobility coefficients, interaction and dilution parameters. The model is implemented in a finite element software package and calibrated with the experimental observations of the four PMBs. The experimental results are well reproduced by the model, and it is thus believed that the calibrated parameters can represent the four PMBs. The simulation results indicate that the model proposed in this paper is capable of capturing the stability differences among the four PMBs and their distinct microstructures at different temperatures. Due to the transition of some PMBs from the thermodynamically stable state at 180°C to the unstable state at 140°C, a homogenization process may occur during the cooling applied numerically. After the transition, the PMBs start to separate into two phases and gradually form the binary structures controlled by the temperature. It is indicated that the cooling rate slightly affects the final pattern of the PMB binary microstructure, although the process can be more complicated in reality due to the potential dynamic reasons.

Microstructure evaluation of polymer-modified bitumen by image analysis using two-dimensional fast Fourier transform

“…At a decreased temperature, the area fraction of polymer-rich phase becomes less in both PMB1 and PMB2. This means the polymer swells less at a lower temperature, which is a reasonable trend for PMB [45]. PMB3 goes through a transition from the thermodynamically stable state at 160 °C to the unstable state at 120 °C.…”

Use of plasticizers in the production of PMB, as a tool for creating effective binders

“…Let's consider the "polymer -plasticizer" system for the most characteristic plasticizers under a microscope, Figure 2-4. The distribution, extent, and homogeneity of various phases in sistems largely depend on various factors, including plasticizer [10][11][12][13][14][15][16]. The recorded difference in the systems is obvious.…”

The use of solubility parameters and free energy theory for phase behaviour of polymer-modified bitumen: a review

“…The analysis in the previous section indicates that the free energy of PMB system determines its thermodynamic stability and phase behaviour towards the equilibrium. To express PMB free energy, the Flory-Huggins theory was employed as a basis (Liang, Xin, Fan, Wang, Jiang, et al, 2019;Liang, Xin, Fan, Wang, & Sun, 2019;Zhu et al, 2016Zhu et al, , 2017aZhu et al, , 2017b. The Flory-Huggins theory was originally proposed for polymer solutions and blends with dominating weak interactions, i.e.…”

“…It is believed that the Hansen solubility parameters and solubility bodies in the three-dimensional (3D) Hansen space are useful tools for analysing PMB storage stability, although no kinetic factors have been considered for this approach. Some other studies (Liang, Xin, Fan, Wang, Jiang, et al, 2019;Liang, Xin, Fan, Wang, & Sun, 2019;Masson, Collins, Robertson, Woods, & Margeson, 2003;Varma, Takeichi, Hall, Ozawa, & Kyu, 2002;Zhu, Lu, Balieu, & Kringos, 2016, 2017a, 2017b, however, adopted the thermodynamic approach and free energy theory to understand PMB phase behaviour. For example, Zhu, Balieu, Lu, and Kringos (2017b) proposed a phase-field model for predicting the PMB phase separation behaviour.…”