Date of Award
Doctor of Philosophy
Civil, Construction, and Environmental Engineering
R. C. Williams
Over the past decades, reclaimed asphalt pavement (RAP) materials have been increasingly used in asphalt pavements due to their significant contribution in reducing asphalt production costs and energy consumption. The main drawback associated with using RAP materials is the excessive amount of stiffness which the aged RAP binder introduces to the mixtures, thus reducing the resistance of mixtures to rutting, stripping, fatigue, and thermal cracking. In response to these limitations, researchers have suggested different techniques to avoid such distresses. The most common technique which is widely being practiced recently, is to use rejuvenators in the mix designs.
Currently, there are many rejuvenators available in the market with many variations in their origins and description. A successful rejuvenator is one that can be applied to the mix design in low dosages while restoring the chemical and rheological properties of the aged RAP binder as well as improving the performance of mixtures to adequate levels. Several petroleum-based rejuvenators have been used in the asphalt mix designs successfully, and recently, bio-based rejuvenators have attracted the attention of researchers due to the value they add to the sustainability of infrastructures.
In this research, two bio-based rejuvenators, one a by-product of the paper industry, and one derived from soybean oil, are introduced to enhance the properties of asphalt mixtures containing 50% RAP materials, and their respective binders. The first bio-rejuvenator is recommended by the manufacturer to be applied directly to the RAP, and then to the mixture, while the second bio-rejuvenator is recommended to be blended with the virgin binder, and then the blend added to the mixture.
In the first phase of the study, the alternative binders were produced based on the proportions in the mix design. First, the RAP binders were recovered from the coarse-graded and the fine-graded RAP mixtures in accordance with ASTM standards. A control binder containing 62.4% virgin binder and 37.6% RAP binder was compared with the two rejuvenated binders containing same amount of RAP binder, smaller amount of virgin binder, and a low dosage of the rejuvenators. The initial screening of the binders in terms of their density, viscosity, and performance grade was done according to the AASHTO standards. For the rheological properties evaluation, binders were tested in three aging conditions: unaged, RTFO aged, and RTFO+PAV aged, using a dynamic shear rheometer (DSR) and a bending beam rheometer (BBR). The complex modulus master curves of the binders were constructed based on the two common models: Sigmoidal and Christensen-Anderson- Marasteanu (CAM). The compatibility of the rejuvenators with the RAP and virgin binder was also assessed using a differential scanning calorimetry (DSC) equipment. The results of this phase proved that the rejuvenators can effectively improve the low and intermediate-temperature properties of the control binder, as well as reducing the complex modulus and viscosity, and decreasing the critical high-temperature performance grade. Statistical analysis on the two master curve models indicated no significant differences between the measured and predicted complex modulus data, and no significant differences between the two models at unaged and RTFO-aged conditions. At PAV-aged conditions, a greater R2 value was observed for the Sigmoidal model. Viscosity measurements with the conventional method using a viscometer revealed a decrease in the viscosity of the control binder with the use of rejuvenator. Further study on the complex viscosity of the binders using the DSR equipment indicated statistically significant decrease in the zero shear viscosity (ZSV) values when using the two rejuvenators. From the DSC results the compatibility of the rejuvenators with the binder was validated and possible disaggregation of some of the asphaltenes was observed.
In the second phase of the research, because the effectiveness of the rejuvenators was of interest at different mixing locations, asphalt mixtures were mixed in two locations: in the lab, and at the asphalt plant where the large-scale phase of the project was being handled. The plant-produced mixtures where then transported to the laboratory and both the plant-produced mixtures and lab-produced mixtures where compacted in the lab using a gyratory shear compactor (GSC). The specimens were then tested for their dynamic modulus, rutting and stripping resistance, and thermal cracking resistance. For the fatigue resistance, asphalt mixtures were compacted in the shape of slabs using a linear kneading compactor. Testing on the specimens was conducted in accordance with the ASTM/AASHTO standards. The dynamic modulus results indicated lower stiffness of the mixtures at low, intermediate, and high temperatures with the use of rejuvenators. The flow number of the mixtures as a measure of rutting resistance was also decreased with the use of rejuvenators due to the lower stiffness at high temperatures. Using the Hamburg wheel tracking test (HWT), no stripping inflection point (SIP) was identified before 20,000 wheel passes for the control mixture and both the rejuvenated mixtures and it was an indication of excellent stripping resistance in the mixtures and proved that the positive effect of high RAP content was not diminished by using the rejuvenators. The results from DCT testing on the mixtures revealed significant improvement in the fracture energy of the control mixtures after being rejuvenated. Although a significant improvement was observed in the fatigue resistance of the control binder after rejuvenation, however, no significant improvement was detected for the fatigue life of the rejuvenated mixtures, indicating that the existing beam fatigue procedure needs revision to integrate the effect of high RAP contents on the mix performance.
Sotoodeh-Nia, Zahra, "Effect of mix scale and rejuvenators on the performance of asphalt binders and asphalt mixtures containing 50% RAP materials- a statistical investigation" (2019). Graduate Theses and Dissertations. 17786.
Available for download on Saturday, December 05, 2020