High-fidelity models in computational mechanics, applied in structural engineering and material research, are developed to be accurate, detailed and robust. These models enable new ways of research, such as developing highly-tailored microstructures in materials. To bypass excessive computational times needed to execute these models, Reduced Order Models (ROMs) can be implemented, which reduce the dimensionality of a problem by projecting it onto a reduced-order latent space. While projection-based ROM usually makes use of Proper Orthogonal Decomposition (POD) to obtain a linear basis needed for Galerkin projections, this thesis describes the development of a Variational Autoencoder-based (VAE) approach, which allows for learning a nonlinear latent space. POD-based and a VAE-based techniques are developed and applied for a case study of a simply supported beam, loaded into plasticity by a single movable point load. The ROM results are compared to the Full Order Model (FOM) results. Results are analysed and compared between the POD- and VAE-based techniques, and for different (hyper)parameters within the VAE-ROM results. The results show the VAE-based ROM outperforms POD-counterparts, especially in extrapolation and with the condition that a large enough dataset was used for training the VAE. Of the analysed parameters used for training the VAEs, the influence of dataset size and latent space dimensionality is observed to be significant, while the degree of regularization in the VAE and the activation function are of limited influence. Furthermore, this study shows that the validation loss of a VAE during training is not a good indicator for the performance of the VAE-based ROM, and suggests to consider the VAE-ROM error already during training of the VAE.

This research investigates the co-liquefaction of Arundo donax and PET plastic to assess their potential as feedstocks for producing bio-oil suitable for bio-pavement applications. The study demonstrates the feasibility of using an invasive species like Arundo donax combined with plastic waste for hydrothermal liquefaction (HTL) to generate bio-oil. The experimental design varied three critical parameters— temperature, residence time, and biomass-to-plastic ratio—to optimize oil yield and gross calorific value (GCV). By employing Response Surface Methodology (RSM) and a Rotatable Central Composite Design (RCCD), the study achieved robust statistical modeling, enabling the identification of optimal conditions across 15 experimental runs and two blank experiments. The results indicated that the char produced from both biomass and PET dominated the product distribution, albeit due to different decomposition mechanisms. PET decomposition primarily yielded solid terephthalic acid (TPA), while biomass char resulted from incomplete lignin and cellulose breakdown. The highest oil yield was obtained under severe conditions, highlighting the significant impact of process parameters on product distribution. Analytical techniques such as FTIR and GC-MS revealed the presence of diverse functional groups and confirmed the decomposition of PET into its monomers. XRD and XRF analyses further characterized the char, identifying key structural components and elemental composition. Statistical analysis showed a significant quadratic relationship between oil yield and GCV, with minimal prediction error, indicating the model’s reliability. The optimized bio-oil exhibited a higher benzene content, suggesting enhanced decarboxylation of PET, which was supported by FTIR data. Rheological testing demonstrated the potential of the bio-oil as a rejuvenator for bio-pavements, with bio-char showing promising properties as a filler. Rheological testing using Dynamic Shear Rheometry (DSR) was conducted to evaluate the bio-oil’s potential as a rejuvenator in bio-pavements. The DSR tests revealed that the bio-rejuvenators effectively reduced the stiffness of aged materials, restoring some of the original flexibility and viscous properties lost due to aging. While the oil derived from pure biomass performed slightly better in this regard, the co-liquefied oil still showed promise, particularly in applications requiring a balance between flexibility and stiffness. Additionally, when bio-char was used as a filler in mastic formulations, it exhibited superior stiffness and rutting resistance compared to conventional fillers, although it was less effective in resisting fatigue cracking. Despite the bio-oil’s lower GCV compared to traditional fuels, the process offers a promising pathway toward sustainable energy production. Continued optimization, particularly of the biomass-to-PET ratio and process conditions, could further enhance the fuel properties of the bio-oil, making it a viable alternative for energy and material applications.

The construction industry is a major contributor to waste generation, with construction and demolition waste (CDW) constituting a significant portion of it. This research is centered on developing a technology to separate and recycle two types of plastics, EPS and PU, from cement matrices, along with recycling the cement itself. The goal is to recover high-quality materials for reuse within the construction sector, thereby promoting sustainable practices and enhancing the circularity of construction materials.
The research involved two classes of samples: samples containing cement and PU foam (Class
A) and samples containing cement and EPS foam beads (Class B). Different separation methodologies were employed for each class.
Class A samples underwent mechanical crushing and sieving, followed by electrostatic separation using a vertical triboelectrostatic separator.
Class B samples were successfully separated using mechanical milling and sieving.
The separated PU foam, due to a reduction in particle size during separation, could not be directly reused as insulation. Therefore, it was analyzed using Fourier-transform infrared spectroscopy (FTIR) to assess its quality for recycling into new polyurethane foam products. The FTIR results confirmed the effectiveness of the separation process, yielding clean polymer suitable for reintroduction into the market as a secondary raw material, particularly for particles smaller than 500 μm.
The separated EPS foam beads were reused to cast new insulating cement, and its thermal conductivity was tested. The results demonstrated that the separation process did not compromise the insulation properties of the EPS beads, allowing for their reuse in their original application.
The recycling potential of the separated cement powder was also analyzed. Chemical composition analysis, particle size distribution, and loss on ignition tests indicated its suitability for reuse as a partial cement replacement in new mortar samples. Mechanical tests on mortar samples with varying percentages of recycled cement powder (15% and 30%) and different reactivation temperatures (650°C and 750°C) showed a slight decrease in compressive and flexural strength compared to the reference mortar, particularly for the 650°C reactivation temperature. However, the recycled cement powder reactivated at 750°C and used at a 15% replacement ratio resulted in a 2.75% increase in compressive strength, highlighting the potential for optimizing the recycling process to achieve comparable or even enhanced performance in construction applications.

This experimental thesis explored the technical feasibility of a temperature-controlled dissolution-precipitation process for recycling polyolefin household wastes. An extensive literature review defines the experiment's feed composition and experimental setup. Additionally, it inspects the potential for the process to become a sustainable addition to the existing plastic recycling system along with a basic analysis of the major costs of a commercial plant.
The study involved 5 experiments with the characterization of its outputs. The results demonstrate that the technique can handle common organic contaminates and non-target polymers in the feed without compromising the quality of the polymer product. The polymer products present characteristics that are comparable to the feed, which mostly consist of food-grade packaging. Suggesting the potential application of polymer products in the food and beverage industry, closing the loop for plastic use.

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

Ageing of bitumen has been long-recognized as one of the major reasons responsible for the gradual deterioration of asphalt pavements. Age-hardening of the binder leads to the embrittlement of the overall asphalt mixture, which entails its increased susceptibility to traffic and environmental induced damage. As a result, high maintenance efforts as well as increased expenses are required to allow for an asphalt pavement to reach its expected service-life.
Past research efforts have established a solid background with respect to the implications of bitumen ageing on the overall response of an asphalt mixture as well as on the binder’s physico-chemical properties. In the same framework, studies have demonstrated that the ageing process of bitumen in the field is not solely a function of the bitumen type itself, but rather, added effects have been identified attributed to the mineral matter and the asphalt mixture design parameters.
This thesis attempts to provide a deeper understanding of the effect of mineral aggregates on the ageing of bitumen, and more specifically, the effect of a special fraction of the solid phase in asphalt mixtures, the mineral fillers. Six different mineral fillers were employed in this research, covering a wide range of physical and composition-related (i.e. elemental/mineralogical) properties. Bitumen-mineral filler blends were prepared, according to a single design protocol, and the resulting mastics along with neat bitumen were subjected to accelerated laboratory ageing by means of the Pressure Ageing Vessel.
The rheological (i.e. Dynamic Shear Rheometer) evaluation of the resulting materials and the derivation of ageing indices revealed the overall ability of the mineral fillers, regardless of their individual properties, to mitigate the ageing of bitumen incorporated in the mastics. The chemical (i.e. Fourier Transform-Infrared Spectroscopy) investigation of the materials showed that, in fact, the chemically active mineral fillers catalysed the oxidation of bitumen incorporated in the mastics. These results allowed for the identification of two mechanisms through which the effect of the mineral fillers on the ageing of bitumen occurs. The first one is related to the physical presence of the mineral matter in the mastics, whereas the second one to the developed physico-chemical interactions between the mineral fillers’ particles and the bitumen. Basic mineral fillers were found to be more efficient in reducing the age-hardening of mastics, compared to acidic ones, by allowing for more intensive interactions between the mastics’ constituent materials. Moreover, there are indications that the mineral fillers’ specific surface area also has a primary role to the developed interactions, and, by extension, to the ageing behavior of the mastics.
Finally, in addition to the aforementioned main findings, binders were extracted and recovered from the aged mastics, in an effort to derive further information on the effect of mineral fillers on ageing of bituminous mixtures by investigating the aged mastics’ constituent materials on their individual level. The rheological and chemical examination of the recovered materials did not lead to any further insight regarding the research questions of this study. Instead, features were revealed which manifest that the extraction and recovery of bitumen may not be a suitable approach for the investigation of the research problem addressed in this thesis.

Nowadays, there is a need to reduce noise pollution due to the tyre-pavement interaction, especially in densely-populated areas, such as the Netherlands, where noise pollution is a major concern. A solution to this problem is the development of pavement surfaces with improved noise reduction characteristics. Previous attempts to develop low-noise pavement surfaces were not successful, mainly due to their poor mechanical performance and low durability. In this research the mechanical performance of three different low-noise pavement surface materials is investigated. The study was part of the Ultrastil Wegdek (USW) project in the Netherlands. The materials were evaluated with respect to their moisture susceptibility, stiffness, cohesive strength and bonding with the underlying layer. For three different low-noise road surfaces (LNRS), the stiffness was evaluated by means of dynamic modulus tests. Furthermore, indirect and direct tensile tests were carried out after long- and short-term moisture conditioning to estimate strength degradation. The interlayer bond strength was determined using uniaxial tension tests at dry and wet conditions. To evaluate the bond characteristics, also two-layer porous asphalt systems were tested as reference materials. The results show high difference in their properties as a result of the mixture composition. Especially, considering the effect of moisture is of paramount importance for these highly open-graded mixtures.