Heavy industry is responsible for about a third of global emissions but lags behind in its effort to become carbon neutral. The electrification of industrial processes is a necessary step to achieve this goal. The asphalt industry is a good candidate for decarbonisation, as it currently relies on burning fossil fuels to heat and dry the aggregate used in asphalt production. Instead, aggregates could be heated electrically by using induction heating.

This thesis will investigate the design of an aggregate induction drum heater. A COMSOL model will be developed to aid the design process and predict the heater behaviour. The heater will be powered by a resonant converter, which is modelled in Simulink. A test setup is built to serve as a proof-of-concept for the design and to experimentally verify the models.

The analysis of the simulation and test results show that the model quality is dependent on the description of the material properties. The COMSOL model predicts the temperature of the middle of the heater with reasonable accuracy while the Simulink model is able to simulate the coil current and converter voltage waveforms with little error. The design of the aggregate induction heater could be improved by thermally insulating the outside surface and increasing the contact area between the aggregate and the heater.
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Asphalt pavements play a crucial role in constructing durable and sustainable road infrastructure. In recent years, with the advancement of sustainability and circular economy goals, reclaimed asphalt (RA) has been widely used in road construction. While the use of RA effectively reduces resource consumption and environmental impact, research on the fatigue and healing performance of asphalt mixtures and binders with high RA content remains relatively limited. This study aims to evaluate the healing performance of binder components from three asphalt mixtures commonly used in the base layers of Dutch pavements, employing multiple healing test protocols and healing indices. Two of these binders contain a high proportion of RA bitumen.

To achieve the research objectives, fatigue and healing tests were conducted on three different asphalt binders: Binder 1, composed entirely of fresh bitumen; Binder 2, a blend of high RA content bitumen with softer fresh bitumen; and Binder 3, which includes high RA bitumen content, fresh bitumen, and the rejuvenator. Fatigue performance was evaluated using Time Sweep (TS) and Linear Amplitude Sweep (LAS) tests to determine the fatigue life of each binder. Additionally, healing performance was assessed through single-rest period and multiple-rest period Time Sweep Healing (TS-H) tests, as well as Linear Amplitude Sweep Healing (LAS-H) tests. To evaluate healing performance, two different indices were used: the Healing Shift Factor (SFh), based on fatigue life extension, and the Healing Index (HI), based on modulus recovery.

The differences between single and multiple rest periods TS-H tests highlight the limitations of single rest period tests in fully capturing material healing capacity, indicating that more complex loading patterns should be explored for more comprehensive assessments. The variations in healing potential results across different test protocols and indices suggest that the healing performance of binders is highly sensitive to test protocol and indices selection.

Based on the described approach, a better understanding of the healing performance of different asphalt binders is achieved. Conclusions and future recommendations for research in this field were provided at the end of this research. ... Read more

The Netherlands has one of the densest road networks with over 140,000 km of roadways. Fatigue cracking is an important distress in flexible pavements. This form of distress results from the application of repeated traffic loading which causes failure. Fatigue cracking assessment on various base layer asphalt mixtures including reclaimed asphalt pavement materials and recycling agents has been addressed in this research work. This research work aims to develop a method for quantifying and assessing this fatigue characterization including the self-healing mechanism of asphalt mixtures using Visco Elastic Continuum Damage Theory. The self-healing in asphalt mixtures was assessed by incorporating group-rest healing periods in a self-developed laboratory testing method. The reliable self-healing models for asphalt mixtures with recycled asphalt materials and recycling agents based on temperature, damage state, and rest periods were predicted using the damage characteristics curve (C-S). Bottom-up cracking in base layer asphalt mixtures was modeled and studied using finite element modeling software FlexPAVE based on the Visco-Elastic Continuum Damage theory. A vivid assessment of mixtures for fatigue and healing characterization is discussed in this research work.

This research work is interrelated with an ongoing project, which aims at developing a protocol to determine the shift factors for the fatigue life of asphalt mixtures to correct healing and aging. The project runs under the umbrella of Knowledge-based Pavement Engineering (KPE), a joint program among Rijkswaterstaat, TNO, and TU Delft. Dura Vermeer is contributing partner to this MSc graduation research work as well.
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The increasing traffic load has led to the use of polymer modifiers in bituminous mixes in order to improve the performance and the durability of the pavement structures. Epoxy is a thermoset material which ensures enhanced fatigue performance and improved mechanical characteristics when used to modify bituminous materials. However, unlike conventional modification techniques, a series of experimental methods have to be conducted to evaluate the chemical- related phenomena occurring during the binder production and their effects on the performance of the epoxy modified bitumen. For this reason in this thesis, the utilization of epoxy modifiers was investigated at binder level.
Initially, the chemical hardening (curing) process of epoxy modified bitumens (EMBs) was investigated by means of Fourier Transform Infrared (FT-IR) spectrometer and Dynamic Shear Rheometer (DSR). Different combinations of hardening conditions for three epoxy modification levels were studied. Properties, such as modulus and viscosity, were utilized to determine the workability of EMB. At the same time, by using the FT-IR spectrometer, the functional groups of EMBs during the chemical reactions were identified for the understanding of polymerization in the epoxy components.
Additionally, the DSR device was utilized to determine the fatigue and tensile strength of EMBs. It was found that, with increasing the content of epoxy modifier, the fatigue life and tensile strength were increased significantly compared to an unmodified binder.
Finally, the age hardening (aging) of EMBs was evaluated at different time intervals. For the simulation of short-term aging on EMBs, a short-term oven aging method (STOA) was used. For long-term aging, simulations were performed in a pressure aging vessel (PAV) under constant pressure and temperature. The results of chemical characterization and rheological properties of the aged EMBs were obtained by using DSR and FT-IR and were compared to the unmodified bitumen.
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The use of synthetic fibres has been reported to enhance the performance of asphalt pavement materials in terms of permanent deformation, fatigue and thermal cracking. However, limited results about the benefits of synthetic fibres in the reinforced warm-mix asphaltic materials, and the exact mechanism of reinforcing the binding part in pavement structures is still unclear. This research aims firstly to examine the material at the warm mixed mortar level using a combination of two synthetic fibres (aramid and polyolefin) to conclude its fracture performance. Several laboratory tests were performed using specially designed experimental tools. Samples of three different fibre contents (0.05%, 0.1% and 0.5% of specimen weight) and two fibre lengths (19 and 38mm) were evaluated. In particular, pull-out tests, whose objective was to explore the interaction of fibre-matrix demonstrated a matrix-type of fracture; meaning that the adhesion of fibre-matrix is higher than the strength of the matrix itself, which implies a benefit of adding fibre to a mixture at high service temperature.
Summary
Moreover, direct tension tests were carried out with both monotonic and cyclic loading to measure the effect of the synthetic fibres on tensile strength, fracture energy and fatigue life of reinforced warm mixes under monotonic and cyclic tension load, respectively. These tension experiments concluded improvements on mechanical characteristics of warm mixed asphalt mortars when fibres were added, mainly applying higher dosages than the recommended by the fibres supplier. Overall, the current results elucidated that implementing dedicated material studies at micro-scales can assist on understanding the material performance and tailoring systems beyond sometimes recommended reinforcement dosages by the suppliers. Finally, a semi-circular bending test was performed as the largest scale of this research using various fibre amount composition as well as fibre length inside the bituminous mix, and the final results mainly correspond with the other examinations that have also been conducted. Therefore, the research methodology utilised in this thesis has been able to examine the reinforcement effect brought by the integration of synthetic fibre to failure performance of the warm mixed asphaltic mixture specifically regarding the cracking resistance extensively. ... Read more