Dissertation
Evaluation of high-RAP asphalt mixtures containing rejuvenators using image processing, binder rheological and mixture performance tests
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2019
DOI: 10.17077/etd.005166
Abstract
For many years, asphalt industry has faced an increased cost in supplying asphalt materials in paving roads. Thus, the idea of incorporating higher amount of recycled materials came into play. However, asphalt agencies have confined the use of recycled materials in asphalt mixtures up to less than 25% since recycled materials contain stiff aged binder which might cause pavement distress such as fatigue and thermal cracking.
The main purpose of this research is to investigate the feasibility of using rejuvenators to increase the RAP content in asphalt mixtures by conducting a comprehensive set of binder and mixture tests. Binder tests include Cryo-SEM, Fourier Transform Infrared (FTIR) Spectroscopy, Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR) and Block cracking tests. Mixture tests to evaluate the performance of high-RAP mixtures containing optimum dosage of rejuvenators include Hamburg Wheel Tracking (HWT) and Disk-shaped Compact Tension (DCT) tests to evaluate the rutting (along with moisture sensitivity) and thermal cracking performance, respectively. In addition, a field test section was constructed to compare high-RAP asphalt mixtures with and without rejuvenators.
The results of Cryo-SEM test showed that rejuvenators are effective in reducing the number and length of cracks in aged binder as the Fracture Index (F.I.) for rejuvenated binder were lower than the aged binder. FTIR test indicates that rejuvenators decrease the aging indexes; however, the reaction between rejuvenators and aged binder is more physical than chemical. DSR and BBR test results proved that rejuvenators soften the aged binder as their PG decreased after mixing with rejuvenators. The block cracking problem of RAP binder was solved after rejuvenating. Mixture tests showed a promising effect of rejuvenators as they did not soften high-RAP mixture excessively, so all samples passed HWT test. From the DCT test, it can be concluded that rejuvenators (except one type) enhance the low-temperature cracking properties of asphalt mixtures without sacrificing the bond between aggregate and binder. Lab-produced and core samples from the test section were tested using HWT and DCT test equipment. Rejuvenated mixtures showed similar and, in some case, better performance than control high-RAP mixtures although the percentage of RAP materials in control mixtures was 12% higher. In conclusion, incorporating rejuvenators is an effective approach to increase RAP contents in asphalt pavements.
Details
- Title: Subtitle
- Evaluation of high-RAP asphalt mixtures containing rejuvenators using image processing, binder rheological and mixture performance tests
- Creators
- Ali Mokhtari
- Contributors
- Hosin (David) Lee (Advisor) - University of Iowa, International ProgramsPaul Hanley (Committee Member)M Asghar Bhatti (Committee Member) - University of Iowa, Civil and Environmental EngineeringSalam Rahmatalla (Committee Member)Aixin Tan (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Civil and Environmental Engineering
- Date degree season
- Autumn 2019
- DOI
- 10.17077/etd.005166
- Publisher
- University of Iowa
- Number of pages
- xiii, 101 pages
- Copyright
- Copyright 2019 Ali Mokhtari
- Language
- English
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 99-101).
- Public Abstract (ETD)
Pavement recycling is a growing technology for practical and economic rehabilitation of existing paved roadways for economical and environmental reasons. Thus, there is an increasing demand to incorporate higher amounts of recycled materials in asphalt mixtures. However, recycled materials might have lost their original properties during their first service life. It could cause major problems if they are used in new asphalt pavements without applying any methods or technologies to improve their engineering properties. This study aims to use rejuvenators to restore the original properties of asphalt mixtures containing high amount of recycled material by adding a type of additives called rejuvenator. It is claimed that rejuvenators can bring back lost original components to the stiff aged binder, so the rejuvenated binder can perform as original virgin binder.
To fully investigate the effect of rejuvenators in high-recycled asphalt mixtures, a variety of binder and mixture tests were considered. A pavement test section was also constructed to evaluate the real performance of rejuvenators when implemented on roads.
The results of this study showed a promising effect of adding rejuvenators to high-recycled asphalt mixtures as the rejuvenated binders were softer and less aged. Less number of thermal cracks was observed from crack-detected images and rejuvenators solved the problem of block cracking existent in aged binder. Mixture performance tests were also conducted to evaluate the strength, moisture sensitivity and low-temperature cracking of high-recycled asphalt mixtures. Results of mixture tests from lab-compacted and field samples indicated that high-recycled mixtures perform better when rejuvenator are added when constructed. In conclusion, the dosage and type of rejuvenators are two key factors affecting the performance of rejuvenated mixtures.
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9983779799402771
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