Application of Bio-Binders as Sustainable Alternative to Conventional Asphalt Binders
Open Access
- Author:
- Barzegari, Saman
- Graduate Program:
- Civil Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 04, 2019
- Committee Members:
- Mansour Solaimanian, Dissertation Advisor/Co-Advisor
Mansour Solaimanian, Committee Chair/Co-Chair
Shelley Marie Stoffels, Committee Member
Aleksandra Z Radlinska, Committee Member
Stephen C Chmely, Outside Member
Patrick Joseph Fox, Program Head/Chair - Keywords:
- bio-binder
asphalt binder
rheology
sustainability
alternate binders
asphalt pavements - Abstract:
- Construction of asphalt pavements, which are the most common type of pavements in the world, is heavily reliant on various non-renewable resources such as aggregates and petroleum-based asphalt binders. A crucial step toward developing a sustainable transportation infrastructure is reducing this dependency and shrinking the environmental footprint of the industry by replacing asphalt binders with alternative sustainable materials. Production of asphalt binders is known as the most energy demanding process involved in asphalt pavement construction, consuming over 40% of the energy in the industry. This results in release of substantial quantities of greenhouse gases, the main contributor toward climate change. This, along with steady increase in the price of asphalt binder due to higher demand, lower production and diminishing resources, warranted various studies to find sustainable alternatives for asphalt binders. One potential group of materials for this purpose are bio-binders. Bio-binders are made through processing of bio-oils, which are produced through thermochemical liquefaction of various biomass feedstocks. Due to variability of the source biomass, these bio-binders have varying properties, and require in-depth investigations. Majority of studies in this field have reported that bio-binders and their blends with asphalt binders (bio-asphalts) suffer from severe aging, hence, recommended limiting the replacement ratio of these materials to minimize the impact of this problem. This study was aimed toward evaluating the possibility of replacing substantial quantities of asphalt binder with bio-binders, and involved conducting thorough physical, rheological, chemical and performance evaluation of bio-binders and bio-asphalts. Four different bio-binders sourced from switchgrass, oakwood, and two blends of pine wood were used in this study. Results confirmed that all bio-asphalts are experiencing severe aging, which results in deterioration of the low-temperature properties of bio-asphalts. Hence, a practical method was sought for improving the low-temperature properties of bio-asphalts. This method, which was based on adjusting the properties of the aged bio-asphalts to match with the properties of aged base asphalt binder, involved addition of small quantities of rejuvenator to the bio-asphalts, and was found to be able to successfully offset the changes in properties of the bio-asphalts due to severe aging of the bio-binders. While having comparable long-term aged properties, the rejuvenator-modified bio-asphalts were found to be significantly softer than the base binder, which could be translated to lower construction and compaction temperatures, further reducing the energy demand of the asphalt pavement construction. Chemical experiments revealed that the upgrading process reduced the water and light-weight components content of the bio-oil significantly. Bio-binders were found to have significantly different chemical composition compared with conventional asphalt binders, having high water, low weight and polar molecule content. This significant difference between the chemical properties resulted in lack of chemical interaction between the two materials, hence, bio-asphalts were found to be a two-phased material, consisting of small droplets of bio-binders physically dispersed within the asphalt binder medium. Existence of free bio-binder particles can be problematic, as the bio-binders and asphalt binders have significantly different aging susceptibility. As the aged bio-binders were found to have highly different properties compared with asphalt binders, these aged droplets of bio-binder can affect the performance of mixtures made with bio-asphalts. Hence, a comprehensive mixture study was conducted to evaluate the performance of bio-asphalts in mixtures. Results of the study showed that bio-asphalt mixtures were in general showing less desirable properties at the same temperatures compared with the mixture made with conventional asphalt binders. This inferior performance was partly due to the softer nature of bio-asphalts compared with the base asphalt binder at the same temperatures. The softer nature of the bio-asphalt was caused by inclusion of rejuvenator to enhance the low-temperature properties of bio-asphalts. However, it was found that the mixtures made with bio-asphalts with no rejuvenator were less flexible compared with the control mixtures. This loss of flexibility can be due to the presence of severely aged bio-binder droplets in bio-asphalts, weakening the bond between aggregates and the bio-asphalts. Additional steps are required to facilitate the chemical interaction between asphalt binder and bio-binders, to eliminate the two-phase nature of bio-asphalts, which in turn can result in bio-asphalts with higher resistance to aging and better mixture performance.