Physical hardening (PH) significantly affects bitumen's low-temperature performance. This paper investigates the effect of oxidative aging and wax structure on PH using 4-mm dynamic shear rheometer (4-mm DSR) and differential scanning calorimetry (DSC) tests. The results show that the wax chain length has a pronounced effect on the PH. Short-chain waxes, such as C18 and C24 affect the PH while longer-chain n-paraffins like C40 or Sasobit have almost no effect. In addition, the physical hardening index (PHI) is not linearly increasing with wax content but shows a maximum at a particular wax percentage. Wax-doped samples that crystallize before reaching the hardening temperatures typically show a reduced PHI compared to those with crystallization temperatures just below the hardening temperature. When crystallization and melting temperatures are not close to the hardening temperatures, the PHIs are typically reduced. Oxidative aging also influenced the PHI and in most cases the hardening decreased after aging. The highest PHI of almost all investigated samples occurs at 0 °C among the four typical temperatures. This investigation provides insights in the mechanism of PH and in the relations between wax contents, the hardening temperature, and the PHI. It also shows that while long-chain waxes used as warm mix additives, will not cause a PH risk, short-chain waxes present in pyrolyzed waste plastic, for example, should be handled with care. In addition, PH is also crucial for the intermediate service temperatures and not exclusively for thermal cracking at low temperatures.

An increasing number of researchers and industrial partners have turned towards biomasses as promising materials for bitumen substitution. This exploration has led so far to a number of patented bio-binders from different stream sources, as well as test tracks and small-scale applications. Considering the relatively short period of research behind these materials, the research community has not yet optimised the design and production of a bio-binder that can completely or partially substitute bitumen in a successful and efficient way. This short review provides an overview of the approach and results of the most significant bio-binder patents and applications thus far. The overview covers a range of materials like natural resin, microalgae and lignin, and innovations like coloured pavements and test tracks with combined bio-materials. It highlights that some materials resulted in good cracking and rutting resistance, while others reported viscoelastic properties similar to bitumen. Finally, this short review stresses the need for a deeper understanding of the fundamental principles and the interaction mechanisms of the materials, which are essential for future research and applications of bio-sourced materials in the asphalt field.

The road infrastructures allow different type mobilities, and social and economic interactions and activities. However, current road infrastructure systems are rarely imagined and designed to overcome the main societal and environmental challenges such as the GHG emissions or the lack of finite and sometimes critical raw resources. Therefore, troubles due to their construction and lifetime cannot be ignored. It is thus central to identify methods to mitigate their overall undesired impact and make them more sustainable over the years. The valorisation of biomaterials, mainly from wastage of different industries, has emerged as a way to make the current transport infrastructure more sustainable. Toward the use of biomaterials as alternative pavement materials it is hence central to identify current barriers and encouraging opportunities to their implementation in the current research and practices ecosystem. Using a literature review and meta-analysis methodology, the goal of the study is to raise awareness and consciousness on the likely limitations in the development of pavement with biomaterials, the changes opportunities and the required areas of research to consider to overcome the identified barriers, and propose a roadmap allowing to reach a cutting-edge development toward sustainable pavement research during the full cycle of the materials.

Physical hardening (PH) is an important factor affecting the low-temperature performance of bitumen. At present, most PH characterizations are performed by the bending beam rheometer. To present an alternative method based on the Dynamic Shear Rheometer (DSR) equipment, this paper explores the possibilities of the 4 mm plate-plate test to investigate PH in bitumen. A variety of binders was selected, differing in their content of natural waxes, in crude origin, and production procedure. An aged sample was also included. The results show that a 20 min equilibrium period is sufficient to stabilize the sample temperature. To evaluate the PH, a time follow-up of 4 h was selected, as after 4 h the change in slope of complex modulus versus time drops below 1%. Further conclusions show that the physical hardening index (PHI) of bitumen is temperature- and frequency-dependent. This PHI is largest at 0 °C and increases when tested at lower frequencies. The non-waxy binder had almost no hardening, while the waxy binders showed evident hardening. Although the presence of wax is an important factor, the PHI of these binders is not directly related to the total wax content, which was determined by differential scanning calorimetry. In conclusion, the findings show that 4 mm DSR tests provide an effective approach to characterize PH of bitumen.

Fibres have been introduced in the asphalt industry to improve the tensile strength and cracking resistance of pavement. In parallel, ageing is considered one of the causes of asphalt’s deterioration. However, little research has described the effect of ageing when different types of fibres are incorporated into bitumen. Accordingly, this paper utilises different combinations of polypropylene, glass and basalt fibres in a conventional bituminous binder. Next, the fibre-reinforced binders are exposed to typical short- and long-term ageing protocols. A systematic evaluation of meaningful rheological indicators via a Dynamic Shear Rheometer (DSR) gives a more clear view of the role of each fibre type and the balance between the reinforcement potential and bitumen’s degradation due to ageing. In parallel, the assessment of ageing-related indices by Fourier Transform Infrared (FTIR) spectrometer contributes to a better understanding of their rheological evaluation.