Grantee Research Project Results
2023 Progress Report: Recycling of Asphalt Pavements Using Environmentally Benign Recycling Agents
EPA Grant Number: SU840414Title: Recycling of Asphalt Pavements Using Environmentally Benign Recycling Agents
Investigators: Hochstein, Daniel , El-Hakim, Mohab , Hangun-Balkir, Yelda , Dano, Christian , Casale, Angelo , Cooke, Kaitlyn
Institution: Manhattan College
EPA Project Officer: Harper, Jacquelyn
Phase: I
Project Period: July 1, 2022 through June 30, 2023 (Extended to June 30, 2025)
Project Period Covered by this Report: July 1, 2022 through June 30,2023
Project Amount: $25,000
RFA: 18th Annual P3 Awards: A National Student Design Competition Focusing on People, Prosperity and the Planet (2021) RFA Text | Recipients Lists
Research Category: P3 Awards , P3 Challenge Area - Sustainable and Healthy Communities
Objective:
The purpose of this project is to investigate the feasibility of using environmentally benign plant-based oils as rejuvenators (recycling agents) to assist in the recycling of asphalt pavements. When asphalt pavement reaches the end of its service life, it is milled into small fragments known as reclaimed asphalt pavement (RAP). RAP is composed of both aggregate (stone or sand) and a thin surface layer of asphalt binder. The asphalt binder on the surface is harder and less durable than virgin asphalt binder due to oxidation that takes place during its service life. RAP is routinely recycled into new asphalt pavements, along with virgin aggregate and asphalt binder. A typical RAP content is around 20%, because larger quantities tend to decrease the strength and durability of the resulting asphalt pavement. This decrease in material properties is attributed to the aged/oxidized asphalt binder on the surface of the RAP.
In order to increase the amount of RAP that can be recycled into new asphalt pavements, oils known as recycling agents or rejuvenators are added. The purpose of these rejuvenating oils is to mix with the aged asphalt binder and restore its physical and mechanical properties to its unaged condition. Current rejuvenators include petroleum-based and environmentally harmful materials. The oils investigated in this study are both environmentally benign and plant-based. The effectiveness of the rejuvenating oils was assessed by:
- Measuring the viscosity of unaged, aged, and rejuvenated asphalt binder.
- Conducting performance testing on unaged, aged, and rejuvenated asphalt binder.
- Conducting strength tests on hot-mixed asphalt (HMA) specimens prepared using RAP and environmentally benign rejuvenators.
Additional testing will be performed during the following one year no-cost extension, this includes:
- Additional performance testing of unaged, aged, and rejuvenated asphalt binder.
- Additional strength tests of hot-mixed asphalt (HMA) specimens prepared using RAP and environmentally benign rejuvenators.
Progress Summary:
- Selection of Oils
The three environmentally benign oils selected were camelina sativa oil, mustard oil, and algae oil. They were chosen based on the following criteria:
- Plant-based.
- Non-toxic to the environment.
- Can be economically produced in the United States.
- Low fertilizer requirements.
- Non-edible (do not compete with a food source).
Camelina oil grows quickly in areas that are not used for farming; is tolerant of cold weather, drought, and low-fertility soils; and has lower water, pesticide, and fertilizer requirements than other traditional oilseed crops. The production cost for camelina oil is substantially lower than other crop oils like soybean or corn oils and in recent years, camelina oil was utilized in biodiesel production.
The mustard plant has a high adaptability, can compete strongly against weeds, and has drought-resistance features. It is also able to thrive in soils polluted with heavy metals due. Mustard oil is non-edible because it contains high levels of erucic acid which can be detrimental to human health. Mustard oil is currently used in the production of biodiesel or soap.
Currently, open ponds and enclosed photobioreactors are commonly used for microalgae production. After which, the microalgae biomass needs to be harvested and the oil is removed through solvent extraction. Currently, algae oil is utilized for food and beverages, personal care and cosmetics, pharmaceuticals, animal feed, nutraceuticals, and biofuels.
- Viscosity of Rejuvenated Asphalt Binder
Asphalt binder was aged using the Universal Simple Aging Test (USAT). This procedure uses thermal oxidation to accelerate the aging process of asphalt binder so that after 40 hours and 45 minutes of exposure to elevated temperatures, the asphalt binder has similar properties as the asphalt binder contained on the surface of RAP. The USAT procedure involves using a convection oven to subject an 8.76g film of asphalt binder with a thickness of 300 mm to a temperature of 150oC for 45 minutes followed by 100oC for 40 hours. Fourier Transform Infrared Spectroscopy (FTIR) was used to measure the chemical changes that took place during the USAT procedure. The asphalt binder was analyzed using FTIR before USAT, after the initial 45 minutes at 150oC, and after the USAT procedure was complete. The FTIR analysis showed that there was an increase in the both sulfoxide and carbonyl function groups, which are indicators of asphalt binder oxidation.
The viscosity of the unaged, aged, and rejuvenated asphalt binder was measured at 135oC using a rotational viscometer. The rejuvenated asphalt binder was prepared by using an overhead mixer to blend the aged asphalt binder with various doses (5%, 10%, and 15%) of the three rejuvenating oils at 120 RPM for 3 minutes. The USAT procedure caused the viscosity of the asphalt to increase from 442.5 mPa-s to 1467 mPa-s. All three of the rejuvenating oils were able to reduce the viscosity of the aged asphalt to its unaged value. By fitting a log-linear trendline through the data, the doses of rejuvenating oil necessary to restore the unaged viscosity were calculated to be 10.5% for camelina oil, 12.2% for mustard oil, and 12.6% for algae oil.
- Performance Testing of Rejuvenated Asphalt Binder
The ability of the rejuvenated asphalt binder to have the necessary mechanical properties to satisfactorily perform as part of an asphalt pavement was assessed through the use of a dynamic shear rheometer (DSR). Testing was performed using a 25mm plate, with a 1 mm gap, at a temperature of 64oC, and a strain rate of 10 rad/sec (1.59 Hz) in order to calculate the rutting parameter. The AASHTO material specification for asphalt binder states that the value of the rutting parameter cannot be less than 1 kPa. If it is less than 1 kPa, then the resulting asphalt pavement is in danger of failure due to permanent long-term deformations known as rutting.
Asphalt binder was first aged using a rolling thin-film oven and then subsequently aged using a pressure aging vessel. The aged binder was then blended using an overhead mixer with various doses (5%, 10%, and 15%) of the three rejuvenating oils at 120 RPM for 3 minutes. The aging procedure caused the rutting parameter to increase from 1.65 kPa to 16.82 kPa. As the dose of the different rejuvenating oils was increased, the resulting value of the rutting parameter decreased. At a dose of 15%, the rutting parameter for each of the oils was less than 1 kPa, indicating that this dose was too high. By fitting a log-linear trendline through the data, the maximum doses of rejuvenating oil so that the rutting parameter does not drop below 1 kPa were calculated to be 12.2% for camelina oil, 13.4% for mustard oil, and 13.7% for algae oil.
- Performance Testing of Asphalt Mixtures with RAP
The strength of the resulting asphalt pavement was assessed by measuring the tensile strength of hot-mixed asphalt (HMA) specimens prepared using RAP and various doses (5%, 10%, and 15%) of the three rejuvenating oils. The HMA specimens were prepared by heating the materials to 165oC in a convection oven, blending them in a 5-gallon mixer, and compacting them using a gyratory compactor. The cylindrical specimens had a diameter of 150mm and a height of 80mm. The strength of the mixtures was determined using the indirect tension (IDT) test. The specimens were loaded at a rate of 50 mm/min and the test was terminated when the load dropped below 1kN. The IDT strength of the control mixture with no rejuvenating oil was measured to be 627 kPa. For each of the three rejuvenating oils, the doses with the largest IDT strengths were a 5% dose of mustard oil with a strength of 716 kPa, a 10% dose of camelina oil with a strength of 618 kPa, and a 5% dose of algae oil with a strength of 604 kPa. For each of the oils, a dose of 15% resulted in the lowest IDT strength.
Future Activities:
The results of this project demonstrate that it is feasible to use environmentally benign plant-based oils as asphalt rejuvenators. The main conclusions are:
- All three oils have shown the ability to restore the viscosity of asphalt binder that has undergone thermal oxidation. This demonstrates that the oils are able to soften the oxidized surface of RAP. Camelina oil proved to be the most effective by requiring the lowest dose.
- Through DSR testing, it was demonstrated that the doses required to soften the aged asphalt binder will not have adverse effects on the long-term durability of the resulting asphalt pavements with respect to rutting.
- Mustard oil was the only oil that was able to increase the strength of the asphalt pavement compared to a mixture prepared without any rejuvenating oils. However, low doses of camelina and mustard oil did not produce a significant decrease in the strength.
Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
sustainable infrastructure, recycled materials, sustainable construction materials, environmentally benign substitute, green chemistryRelevant Websites:
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.