From the pavement construction emission perspective, bitumen emulsion is considered more environment-friendly than conventional bitumen because of its much lower construction temperature. However, bitumen emulsion faces the major concern of low mechanical strength especially at high service temperatures. To improve the mechanical performance of bitumen emulsion, waterborne epoxy resin can be used as a modifier. Nevertheless, there still lacks fundamental understanding on the effects of waterborne epoxy resin on the microstructure and rheological performances of the residual bitumen of the emulsion. To fill this gap, this study aims to investigate the microstructure and develop the constitutive model of the waterborne epoxy resin-modified bitumen emulsion residue (WEBER). To achieve this objective, a confocal laser scanning microscopy was first adopted to characterise the microstructure of WEBER. The frequency sweep tests were then conducted, and the ‘2S2P1D’ model was applied to simulate the WEBER’s dynamic response at different loading frequencies. The results indicated that the waterborne epoxy resin formed a polymer-rich film around the bitumen phase in the emulsion residue when its content reached 3 wt%, and the ‘2S2P1D’ model can well describe the WEBER’s dynamic response at different loading frequencies.

Crumb rubber modified bitumen (CRMB) can be regarded as a binary composite system in which swollen rubber particles are embedded in the bitumen matrix. The current study aims to further improve the prediction accuracy of micromechanical models for CRMB by considering the interparticle interactions. To accomplish this goal, two different strategies were used. Firstly, the (n+1)-phase model was applied to the CRMB system by considering the multilayer properties of swollen rubber particles. Secondly, a new micromechanical scheme called the J-C model was used to account for the interparticle interaction issue. Results show that the (n+1)-phase models slightly increase the prediction accuracy but the underestimation of complex modulus at lower frequencies remains unsolved. The J-C model remedies the underestimation of modulus in the low-frequency range by other models and provides an overall improvement for the relative prediction accuracy by properly addressing the interparticle interactions from the perspective of particle configuration.

In order to study the maintenance strategy of Epoxy Asphalt Concrete (EAC) in low temperature environment, the similarity of four anti-cracking performance indexes (plane strain fracture toughness, bending stiffness modulus, ultimate tensile stress and ultimate elongation linear strain) of EAC were analyzed, and the mathematical model for investigating the relationship between the number of freeze-thaw cycles and the comprehensive evaluation index of the crack resistance of epoxy asphalt mixture (EAM) was established in this paper. At first, the weight of each index is determined by one-way ANOVA. Then the anti-cracking performance of EAC under freezing-thawing condition is evaluated by fuzzy comprehensive evaluation method. The results show that the pavement maintenance bureau needs to carry out the maintenance of epoxy asphalt pavement on steel bridge deck every 30 days (1 month) for ensuring the crack resistance of EAC in winter with low temperature.

As an environmentally friendly alternative for the production of high-performance modified asphalt by chemical reactions, a liquid-state polyurethane-precursor-based reactive modifier (PRM) was developed and employed in the asphalt modification. In contrast to the traditional solid bitumen modifier, for example, rubber and thermoplastic elastomers, the PRM as a liquid modifier has more significant advantages in reducing energy consumption and improving asphalt performance, which has attracted widespread attention. However, the aging resistance and its mechanism are not clear. In view of this, the aging performance of two PRM-modified bitumen (PRM-70 and PRM-90), under the short-term thermo-oxidative aging, long-term thermo-oxidative aging, and ultraviolet (UV) aging conditions, was investigated through chemical and mechanical methods. The results show that the PRM-90 is more susceptible to the thermos-oxidative aging and UV aging. The use of low-penetration-grade bitumen and ensuring an adequate reaction are beneficial to enhance the aging resistance of PRM-modified bitumen. The impact of aging on high-temperature performance of PRM-modified bitumen is great, followed by the low-temperature performance and the anti-fatigue performance. The mechanic-relevant rheological aging index (RAI) and fracture energy index (FEI) are recommended to evaluate aging properties for PRM-modified bitumen. This study not only provides support for further research on the relationship between the aging properties and mechanical performance of PRM-modified bitumen, but also provides a reference for conducting mechanism analysis.

Cracks are one of the main problems that plague road workers. A correct understanding of the internal crack propagation mechanism of asphalt pavement will help road workers evaluate the road’s working status more comprehensively and make more reasonable decisions in design, construction, and maintenance work. This paper established a three-dimensional asphalt pavement layered model using the software ABAQUS and fracture mechanics theory and the extended finite element method were used to explore the mechanical response of the pavement base layer’s preset reflective cracks. This paper investigated the influence of the modulus of each layer, vehicle load on the principal stress, shear stress, J-integral, and two stress intensity factors (K1, K2) during the pre-determined crack propagation process of the pavement base layer, and the entropy method was used to analyze the above-mentioned mechanical response. The results show that the main factor affecting the propagation of reflective cracks on asphalt pavements is the modulus of the bottom surface layer. However, from a modeling perspective, the effect of increasing load on crack growth is obvious. Therefore, in terms of technical feasibility, the prevention of reflective cracks should still be achieved by controlling the driving load and prohibiting overloading.

Rubberized asphaltic materials have been frequently combined with warm-mix asphalt technologies to tackle the issues of high energy consumptions and emissions during construction. Effective and accurate characterization of binder properties is conducive to the improvement of long-term pavement performance. The current study aims to quantify the effects of rubber content and warm-mix additives on rutting and thermal cracking performance of crumb rubber-modified bitumen (CRMB), and explore the rubber and additives modification mechanisms and their impacts on the binder performance. CRMBs containing different rubber contents and warm-mix additives after long-term aging were subject to multiple stress creep and recovery (MSCR) tests and low-temperature frequency sweep tests using a dynamic shear rheometer (DSR) with 4-mm loading plate to investigate the high- and low-temperature performance, respectively. Rheological tests were also conducted on the bitumen and rubber phases of CRMB to understand the rubber modification mechanism. Results show that CRMB binders have superior rutting and thermal cracking resistance due to rubber modification. The improvement of high- or low-temperature performance is more prominent at higher rubber concentrations. The effects of warm-mix additives on the rutting and thermal cracking performance are different. Generally, the wax-based additive improves the rutting resistance but negatively affects the low-temperature performance. In contrast, the chemical-based additive has an opposite effect except for the high-temperature performance of neat bitumen. The stiffening of the bitumen phase and the contribution of swollen rubber particles in the bitumen matrix together contribute to the peculiar viscoelastic response of CRMB, i.e., stiffer/softer and more elastic at high/low temperatures. This modification mechanism explains the superior rutting and thermal cracking performance of CRMB.

The pore-water pressure generated by intermittent dynamic vehicle loading under various saturation states is recognized as a critical factor influencing the behaviour of permeable pavement structures, especially the behaviour of UGB layer. However, the underlying mechanisms of hydro-mechanical interaction in the UGB layer and the influence on the pavement structure are still unclear. This study aims to characterize the changes in dynamic response in permeable pavement structures under various saturation conditions by considering the hydro-mechanical interaction within the UGB layer. To achieve this objective, a full-scale test track with a PUPM wearing course was constructed. Pressures and water distribution were characterized by embedded sensors within different layers of the test track when subjected to the accelerating pavement test. Based on the coupled SAME model, the water distribution and the dynamic response of UGB in the rainfall events were both characterised and solved by FEM. The results predicted by the proposed SAME model correspond to the field measurements, and the influence of the water content on the resilient modulus distribution within the UGB layer was then estimated. Based on the predictions for the stress state of the UGB layer, the sensitivity analysis was also proposed.

Porous asphalt (PA) pavements are widely employed in areas with wet climates. As particle enhancement inclusions in asphalt mastic, mineral fillers play essential roles in improving the performance of PA pavements. This study developed a coupled multiscale finite element (FE) model, involving the mesostructure of PA mixture and PA pavement. Four types of mastic properties were employed with four mineral fillers (Granodiorite, Limestone, Dolomite, and Rhyolite) in the mesoscale portion of the pavement model to analyse the effects of filler types on the performance of pavements. The performances (load-bearing capacity, rutting resistance, and ravelling resistance) of pavements with different fillers were identified and ranked, and their correlations with the chemical components of the four fillers were analysed. The computational results showed that pavements with Rhyolite and Granodiorite fillers have higher load-bearing capacities and rutting resistance, while the Limestone and Dolomite fillers can improve the ravelling resistance of the PA pavements. In the correlation analysis, the chemical components Al₂O₃ and SiO₂ play dominant roles in improving the load-bearing capacities and rutting resistance of the PA pavements, and the fillers with high percentages of CaO can improve the ravelling resistance of the PA pavements.

One of the main drawbacks of crumb rubber modified bitumen (CRMB) is the storage stability issue. The storage instability of CRMB impedes its further application. This study aims to develop a robust methodology to evaluate the storage stability of CRMB binders using both mechanical and morphological tests. The effects of rubber contents (0, 5%, 10%, 15%, 22% by weight of bitumen) and different non-foaming warm-mix additives (wax-based and chemical-based additives) on the storage stability of CRMB were investigated. Laboratory tests were also performed on the constituents of CRMB to have a deep understanding of the mechanism of storage instability. Standard tube separation tests were conducted on different binders. Both rheological tests and X-ray computed tomography (CT) scan tests were performed on the binder samples collected from different parts of the tube test. Separation indices were developed based on the difference in mechanical property and rubber content from the tube samples respectively. Results show that CRMB with a higher rubber content is more storage stable than that with a lower rubber content. The addition of warm-mix additives is detrimental to the storage stability of the studied CRMB. Rheological tests were performed on the individual constituents of CRMB (i.e., bitumen phase and rubber phase) to understand better the dynamic asymmetry potentially existing within the unstable CRMB binder. Results show that the residual bitumen becomes stiffer while the swollen rubber becomes softer after interaction because of the preferential absorption of light components of bitumen by rubber. The dynamic asymmetry existing between the bitumen phase and the rubber phase of CRMB results in storage instability. When the bitumen phase has similar dynamic properties as the rubber phase, the resulted binder system will be stable. It is possible to manipulate raw material properties and interaction conditions to achieve the desired crossover between two phases of CRMB and hence obtain a storage-stable CRMB blend.

To reduce the thermal-oxidative aging of asphalt and the release amount of harmful volatiles during the construction of asphalt pavement, a new composite anti-aging agent was developed. Since the volatiles were mainly released from saturates and aromatics during the thermal-oxidative aging of asphalt, expanded graphite (EG) was selected as a stabilizing agent to load magnesium hydroxide (MH) and calcium carbonate (CaCO₃) nanoparticles for preparing the anti-aging agents of saturates and aromatics, respectively. Thermal stability and volatile constituents released from saturates and aromatics before and after the thermal-oxidative aging were characterized using the isothermal Thermogravimetry/Differential Scanning Calorimetry-Fourier Transform Infrared Spectrometer test (TG/DSC-FTIR test). Test results indicate that anti-aging agents of EG/MH and EG/CaCO₃ effectively inhibit the volatilization of light components in asphalt and improve the thermal stability of saturates and aromatics. Then, the proportions of EG, MH, and CaCO₃ added in the developed composite anti-aging agent of EG/MH/CaCO₃ are 2:1:3 by weight. EG/MH/CaCO₃ plays a synergetic effect on inhibiting the thermal-oxidative aging of asphalt, and reduces the release amount of harmful volatiles during the thermal-oxidative aging after EG/MH/CaCO₃ is added into asphalt at the proposed content of 10 wt. %. EG plays a synergistic role with MH and CaCO₃ nanoparticles to prevent the chain reactions, inhibiting the thermal-oxidative aging of asphalt.

Waste tire rubber has been incorporated into asphalt modification for decades due to its various benefits. There are two main mechanisms during bitumen–rubber interaction: rubber swelling and chemical degradation. This study surveys these two processes from the viewpoint of polymer science. The kinetics of rubber dissolution and thermodynamics of rubber swelling are discussed to provide a fundamental understanding of the interaction process and to demonstrate how optimisation of material selection and processing procedures can lead to the desired binder properties. Factors including the interaction conditions and raw material characteristics are analysed based on the previous theories and compared with experimental results.