Development of mix design guidelines for high performance RAP-predominant asphalt mixtures

Abstract

Incorporation of higher percentages of RAP has always been favorable since it reduces use of raw materials including bitumen and aggregates. Consequently, not only are asphalt mixtures with higher RAP cheaper compared to the ones with lower RAP amount, but they are also more environmentally friendly. This thesis deals with the asphalt mixtures in which the amount of reclaimed asphalt pavement (RAP) prevails the virgin aggregates. So far, utilization of up to 50% RAP in asphalt mixtures has been studied a lot and pavements containing RAP from 10% to 50% have been laid in all corners of the globe. As long as it is less than 50%, RAP is considered as an addition to the virgin aggregates whose gradation must comply with the standard’s recommendation. In contrast, in this study, RAP gradation remains as is in the stockpile and virgin aggregates are added in the minimal amount to correct the gradation. Concepts of Bailey method are used to design different aggregate blends with firm structures. Then, guidelines to prepare asphalt mixtures with very high RAP contents (>50%) is proposed and a mix design based upon simple tests corresponding to different aspects of performance is developed to find the optimum asphalt mixture among others. Since the proposed method is based on simple testing, which must be in order to be viable in all laboratories, it is required to further investigate the behavior and performance of the blends and verify the effectiveness of the mix design. First, behavior of asphalt mixtures and their corresponding binders were studied through dynamic complex modulus testing, 2S2P1D modeling and Shift-HomothetyShift in time-Shift (SHStS) transformation. Then, binder tests were carried out to find the best blending process representing asphalt binder inside asphalt mixtures in order to facilitate studies on effectiveness of rejuvenator that is a must in asphalt mixtures containing very high RAP. Finally, fatigue life as the main concern of the asphalt mixtures with very high RAP content was examined using classical and visco-elastic continuum damage (VECD) approaches. Results indicate the high efficiency of Bailey method concepts in improving rutting resistance. Also, the mix design was found effective though not perfect in ranking different asphalt mixtures with respect to fatigue performance. The framework of the mix design is strong but the fatigue evaluation must be according to advanced testing and analysis since it is a complicated phenomenon. VECD is a better approach compared to classical one in analyzing fatigue life of asphalt mixtures containing very high RAP. With regard to blending process, there was no single blending conditions that can represent exactly all rheological properties of extracted and recovered bitumen from mixtures with very high RAP content. Also, asphalt binder is not an indicative of the behavior of asphalt mixture with very high RAP content at all temperatures and frequencies; it is more impactful and, subsequently, more representative at high temperatures and/or low frequencies.

Date	3 Apr 2023
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Alan Carter (Supervisor) & Luis G. Loria-Salazar (Co-supervisor)