Investigation of the rejuvenator content effect on the mechanical characteristics of cold recycled asphalt mixes

Abstract

Asphalt pavements usually lose their essential bituminous components by the time (as they age) which leads to cracking, brittleness and in general low mechanical properties of the pavement. Therefore, pavements need a partial or full treating (recycling) to prevent its deterioration. Nowadays, aside from the conventional hot recycling methods, cold recycling pavement technologies due to the energy source's limitation and also environmental concerns (eliminating of fume and particle emission to the atmosphere) are highly in demand. Maintenance activities of old pavements (that need rehabilitation) using secondary and waste materials (Reclaimed Asphalt Pavement (RAP) produced by crunching old bituminous pavement) is of important manifestations of the construction potential share in the sustainability goals. Cold Recycled Mixes (CRM) can be made of 100% of recycled materials. However, one of the major challenges in this process is that, the bitumen included in the recycled materials is not usable in the new mix. Therefore, adding a high amount of new bitumen to the base pavement increases the process cost. The use of a rejuvenator could potentially mobilize the aged binder included in the recycled material, and it would change the behaviour of the mix and asphalt binder leading to higher possible amount of RAP usage in the mixture, enhanced cracking and rutting resistance. The positive effect of rejuvenators in the hot asphalt recycling has been approved in the literature. The main objective of the present research was to evaluate the feasibility of using a rejuvenator with cold recycled materials. The specific objectives were to assess the physical and chemical interaction between the RAP and its bitumen content with the additive rejuvenator. This was aimed to quantify the impact of the rejuvenator addition in cold recycled mixes (CRM) rehabilitation (such as new cluster creation) and RAP rheological properties (tensile strength), and its corresponding rehabilitated bitumen properties. The secondary objective was then to optimize the amount of added bitumen to those mixes using effective employment of rejuvenators in different cold mix preparation scenarios. To do so the effect of rejuvenator content in different aspects of asphalt rehabilitation including clustering effect, and rheological characterization of the cold mixes were examined in different conditions of specimen preparation. Several specimen characteristics and specimen preparation parameters such as RAP size, RAP content in the mixture, specimen preparation temperature, curing time, compaction were analyzed in parallel to the rejuvenator content percentage in the mix. Besides, FTIR tests were conducted to find out the whether the rejuvenator effect had a chemical reaction (new chemical bonding) nature or it comes with some physical property modification in the mixture. The studied RAP was collected from the metropolitan area of the Montreal, and SYLVAROAD PR1000 commercial rejuvenator was used for the investigations. Results indicated that although the rejuvenator content could significantly affect the clustering formation in the cold mix, the RAP content and its corresponding size as well as mixture preparation process (compaction and preparation temperature) had significant effect both on the cluster formation and rheological properties of the RAP such as tensile strength in IDT tests. In the case of new cluster formation in the rehabilitated materials, results showed that an increase in the rejuvenator content would result in an increase in the cluster formation. However, this effect was significantly increased when it was combined with the compaction. The same RAP IDT tests revealed that the optimum additive content is significantly affected by the preparation temperature where an increase in the specimen preparation temperature resulted in reduction in the required optimum content of rejuvenator (4% for specimen preparation at 40 ℃ and 7% for preparation at 60 ℃). Furthermore, rehabilitated extracted bitumen analysis showed that an increase in the rejuvenator content in the initial RAP could increase the low temperature and high temperature performance of the bitumen, however, the shear complex modulus suggested 7% additive percentage as the optimum content in this setup of materials. Finally, the chemical bonding analysis in the Fourier Transform Infrared Spectroscopy (FTIR) test could not reveal any effective chemical alteration/production in chemical functional groups of the tested materials as a result of rejuvenator addition in the rehabilitated extracted bitumen. In other words, results suggest that the rejuvenator effects are mostly controlled by the physical modification of the mix such as viscosity reduction, etc).

Date	19 Dec 2022
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Alan Carter (Supervisor) & Sara Bressi (Co-supervisor)