The Faculty of Applied Engineering has a new doctor! Dr. Alexandros Margaritis defended his doctoral thesis on the 9th of December, with professor Wim Van den berg and professor Johan Blom as promotors. The doctoral thesis is titled 'Maximising Asphalt Recycling: challenges and variability in fatigue and healing'.

Most roads worldwide consist of asphalt, a mixture of stones and bitumen, a petroleum product which acts as a binder. The thesis deals with the recycling of asphalt, one of the most recyclable materials. The material milled from a deteriorated road is called reclaimed asphalt (RA). In Belgium, new asphalt mixtures are produced containing in average 40% RA.

Road authorities, contractors and research institutions admit to the economic and environmental benefits of recycling asphalt. Consequently maximising the use of RA captures the strategy and the vision a country must follow for the sustainable growth of asphalt pavements. Adding more RA is not always beneficial in terms of mechanical performance. Therefore achieving acceptable durability standards has particular challenges. Many factors are expected to influence the maximum use of RA. In this thesis, four main aspects were isolated and studied to reveal the impact of incorporating RA on the mechanical performance of asphalt mixtures.

The first two aspects are associated with the two main factors affecting the asphalt mix properties. The first is the ageing state of reclaimed asphalt binder (RAB), which means how aged the RAB is. This aspect is essential for the mechanical performance of the asphalt mix. A new methodology has been proposed, using more advanced techniques, able to provide a more accurate ranking compared to the current methods. Another crucial phenomenon in mixtures with RA is the blending between the old bitumen (the RAB) and the new bitumen. Until now, it was assumed that the two parts are 100% blended. A novel microscopic technique was introduced in this research, able to provide information on how well the two bitumen parts were blended.

Aspects three and four are related to the service life of asphalt mixtures. This is typically measured by the resistance of the asphalt material to cracking, resulted under the repeated traffic loading, also referred to as fatigue resistance. Additionally, asphalt has been identified as a material with self-healing capabilities, meaning that non-traffic loading and higher temperatures allow the material to recover part of its strength. Mixtures with 0%, 40% and 70% RA were tested to evaluate how well they will perform in terms of the two mechanical properties: fatigue and healing.

The proposed methods cover some of the most important aspects a practitioner must take into account when designing and evaluating an asphalt mixture with RA. The results show that the proposed techniques can be effectively applied, providing first with a better understanding on the ageing level and the blending efficiency and then on the impact of RA on the fatigue and the healing properties of asphalt mixtures with RA.