Extensive transportation infrastructure is crucial for enabling efficient transportation and fostering economic development. However, the operation of roadways contributes to escalating environmental and societal issues, including noise pollution and carbon emissions. To achieve a balance between economy, environment, and society, growing focus is being placed on enhancing the durability and sustainability of asphalt pavement in all aspects. A pivotal factor contributing to the deterioration of asphalt pavement performance is the degradation of bitumen properties, significantly affected traffic and climate conditions. The latter is primarily related to two key processes: oxidative aging and moisture in bitumen. Extensive studies have been undertaken to investigate the moisture and ageing behavior while large variations have been reported due to the complexity of these behavior, the diversity of bitumen types, and the variability of environmental conditions. Such discrepancies complicate the formulation of bituminous binders and mixtures that mitigates these issues. The objectives of this thesis are centered on gaining a thorough understanding of the mechanisms behind moisture and ageing behavior in bitumen, working towards a fully coupled moisture and ageing behavior in bitumen and their impact on bituminous materials. To figure out the complex moisture and aging effects in bitumen, it is essential to initiate from a simpler scenario without involving too many variables and then gradually take into consideration more factors affecting the moisture and ageing processes. Guided by this principle, the moisture diffusion behavior in bitumen and its effects on bitumen properties are initially investigated. To obtain fundamental insights into the moisture mechanisms, both experiments and molecular dynamics simulations are conducted for mutual interpretation and corroboration. Results show that the moisture in bitumen consists of three states: free water characterized by a constant diffusion coefficient and a saturated concentration, immobile water bonded to polar functional groups with a maximum concentration dependent on the number of these available groups, and water clusters, whose diffusion coefficient is significantly lower compared to free water and varies with cluster size. The effects of ageing on the physicochemical and rheological properties of bitumen derived from diverse crude oil sources are evaluated and the physicochemicalrheological relationship is elucidated. The direct analysis of specific parameters and the chemometric analysis of full curves obtained from various chemical, physical, and rheological tests are combined for more accurate and extensive characterization. Results provide new insights into the chemo-mechanical relationship of bitumen, demonstrate the high capability of comprehensive information embedded in FTIR spectra and GPC curve in characterizing various rheological properties, and guide the selection of key physicochemical and rheological parameters for the evaluation of bitumen degradation. To characterize the impact of ageing on the moisture diffusion behavior in bitumen including moisture diffusion coefficient and absorption amount, the moisture transport in aged bitumen is measured through dynamic vapor sorption. The key factors determining moisture diffusion coefficient and moisture absorption are fractional free volume and polarity of bitumen. The changes of these two factors with increasing ageing level integratedly lead to increased activation energy for the diffusion of free water and reduced enthalpy of its adsorption. Simultaneously, the ageing kinetics of bitumen films are affected by the presence of moisture. The presence of moisture can inhibit oxidative reaction through the competitive diffusion between oxygen and moisture while the removal of moisture accelerates it due to additional diffusing pathways created by the diffusion of water molecules, especially water clusters. In conclusion, this thesis provides in-depth insights into the understanding and evaluation of moisture diffusion and oxidative reaction in bitumen, as well as their respective effects on bitumen properties. The effects of moisture on the ageing process and that of ageing on the moisture behavior elucidated in this thesis establish a robust foundation for the modelling of fully coupled moisture-ageing effects in bituminous binders. These findings provide valuable guidance for the design, construction, and maintenance of porous asphalt pavement aiming at improved pavement durability and sustainability.@en

Moisture in bitumen and at the bitumen-aggregate interface affects the cohesive and adhesive properties of asphalt mixtures, which are critical for the service performance and durability of pavements. This paper aims to investigate the kinetics and thermodynamics of moisture transport in bitumen at various temperatures and relative humidity for different bitumen types. Transport models are introduced to study the moisture transport mechanisms. A parameter optimization approach combined with the finite element method is applied to simulate moisture transport behavior. Results show salient sorption increase at higher relative humidity levels (more than 70%), indicating the occurrence of clustering of water molecules in bitumen, which can lead to a significant decrease of the diffusion coefficient. Transport models show great quality in simulating experimental results, in which the S-Cluster model provides a detailed explanation of the moisture transport mechanisms and describes better the performance at high sorption levels. The diffusion coefficient, cluster size and activation energy were determined and were found to be linked to the bitumen chemical and structural properties. The transport kinetics and thermodynamics are expected to contribute to a comprehensive understanding of moisture transport behavior in bitumen and further of pavement moisture damage at complex and interacting environmental conditions.@en

Water transport is one of the major factors responsible for moisture damage in asphalt pavements. To study the thermodynamics and kinetics of water transport in bitumen and to uncover microscale mechanisms of moisture-induced damage, molecular dynamics simulations were performed for up to 600 ns for water–bitumen systems with realistic water contents that varied from 0 to 1.76 wt%. Hydrogen bonding interactions and clustering of water molecules at various combinations of temperature and water content were investigated, and their effects on the self-diffusion coefficient of water and bitumen properties are computed and discussed. It is shown that the saturated water concentration in bitumen is small, especially at low temperatures, and additional water molecules tend to form large water clusters via hydrogen bonding, indicating micro-phase separation of the water and bitumen phases inside the simulation box. Hydrogen bonding and water clustering play a crucial role on the magnitude of the self-diffusion coefficient of water. Physical properties of bitumen that include viscosity and cohesive energy are affected by water. The presence of large water clusters is indicative of how degradation in cohesion is observed on the microscale.@en

The chemical characterization of bitumen type and ageing state are fundamental in determining structural and mechanical properties of bitumen. This work aims to classify various bitumen types at different ageing states and to identify the primary chemical differences relevant to the classification. Fourier transform infrared (FTIR) spectral data of eight bitumen types at five ageing states were analyzed using a chemometric procedure that incorporates principal component analysis (PCA), linear discriminant analysis (LDA) models, variable selection methods. The models presented results of high accuracy in differentiating bitumen type and ageing state. The results show that the spectral regions that describe the aliphatic and aromatic bonds are critical to the identification of bitumen types. The chemical changes due to bitumen ageing are mainly revealed at the region of 1800–900 cm-1. This chemometric method is instructive for the characterization of chemical bitumen properties.@en

Oxidative ageing and moisture damage are key factors in bitumen degradation and asphalt pavement deterioration. The effects of oxygen and moisture on bitumen are governed by their transport and reaction processes. This paper provides an overview of theories and concepts developed to describe the kinetics, thermodynamics and mechanisms of transport and reaction of moisture and oxygen within bitumen. The moisture- and oxygen-induced changes of the physicochemical and mechanical properties of bitumen are also discussed. The aim is to summarize literature findings and conclusions and discuss the possibilities of establishing coupled moisture-oxygen models to be used for long-term pavement performance predictions.@en