According to WPB, researchers in Iran have identified pomegranate peel extract as a promising natural antioxidant for reducing the oxidative aging of petroleum bitumen. A study published on October 7, 2026, found that incorporating the plant-derived extract into conventional bitumen could slow chemical changes associated with aging while improving resistance to high-temperature deformation. The research, conducted at Azarbaijan Shahid Madani University, also identified a 1.5% additive concentration as the most balanced formulation among the mixtures tested.
The study, authored by Mehdi Mohammadi, examined whether antioxidant compounds recovered from discarded pomegranate peels could help protect bitumen against the chemical and physical deterioration that occurs during asphalt production and pavement service. Bitumen gradually hardens as it is exposed to heat, oxygen, and environmental conditions, reducing its flexibility and ability to withstand repeated traffic loading. Over time, these changes can increase the risk of fatigue and temperature-related cracking.
The proposed additive relies on naturally occurring polyphenols found in pomegranate peel, including tannins and phenolic acids. These compounds have antioxidant properties associated with their ability to neutralize free radicals involved in oxidation reactions. By limiting these reactions, the extract may reduce the formation of oxygen-containing chemical groups that contribute to changes in bitumen composition and rheological behavior.
To prepare the additive, the researchers collected pomegranate peel waste, dried and ground the material, and extracted its antioxidant compounds using an ethanol–water solution. The resulting concentrated extract was incorporated into PG 64-16 bitumen at four concentrations: 0.5%, 1%, 1.5%, and 2% by weight of the binder. The study therefore evaluated a processed antioxidant extract rather than simply adding untreated pomegranate peel powder to asphalt.
The modified samples were tested before and after simulated short-term and long-term aging. The research combined conventional physical measurements with rotational viscosity testing, dynamic shear rheometer (DSR) analysis, bending beam rheometer (BBR) testing, chemical composition analysis, and Fourier-transform infrared spectroscopy (FTIR). Short-term aging was simulated using the Rolling Thin Film Oven Test (RTFOT), while the Pressure Aging Vessel (PAV) was used to represent longer-term oxidative aging under controlled laboratory conditions.
The results showed that the addition of pomegranate peel extract reduced bitumen penetration values by up to 18% and increased the softening point. These changes indicate a stiffer binder with improved resistance to high-temperature deformation. The high-temperature performance grade increased from PG 64 to PG 70, suggesting improved resistance to rutting under the laboratory performance-grading system.
However, the higher stiffness also introduced an important processing consideration. At the 1.5% dosage, rotational viscosity measured at 110°C increased by approximately 77%. Higher viscosity may influence binder pumping, mixing, coating, and compaction requirements, depending on the production temperature and asphalt mixture design. The researchers therefore evaluated the additive not only according to high-temperature performance but also in terms of workability and low-temperature behavior.
Among the four concentrations tested, 1.5% pomegranate peel extract provided the most balanced results. This formulation improved high-temperature performance and reduced thermal sensitivity while maintaining acceptable low-temperature characteristics under the investigated test conditions. The findings indicate that increasing additive content beyond this level does not necessarily provide a better overall balance of properties.
Chemical analysis provided further evidence of the extract's potential antioxidant effect. SARA testing, which separates bitumen into saturates, aromatics, resins, and asphaltenes, showed that extract-modified binders experienced a smaller aging-related increase in the asphaltene fraction than the untreated binder. This difference was particularly evident after simulated long-term aging using the PAV procedure.
FTIR measurements supported these findings. The modified bitumen containing 1.5% extract showed smaller increases in carbonyl and sulfoxide indices after aging compared with the conventional binder. These chemical groups are widely used as indicators of oxidative changes in bitumen. Their reduced formation suggests that the pomegranate-derived compounds helped limit some of the chemical reactions responsible for progressive binder aging.
For the bitumen industry, the study is significant because it addresses aging at the chemical level rather than relying solely on physical stiffening or conventional polymer modification. Some additives can improve rutting resistance without necessarily slowing oxidation. The pomegranate peel approach attempts to combine antioxidant activity with acceptable rheological performance, potentially creating opportunities for developing bio-based additives from agricultural processing waste.
The technology could also offer a new application for discarded pomegranate peels generated by juice and food-processing industries. However, the environmental and commercial benefits remain to be established. Extract production requires collection, drying, processing, and solvent recovery, and the study does not provide a comprehensive life-cycle assessment or industrial cost comparison with conventional commercial antioxidants.
The results are limited to laboratory testing of bitumen binder. The study does not establish how the modified binder performs in full asphalt mixtures under traffic loading, changing weather conditions, or extended field exposure. Further research would be required to assess mixture-level fatigue and cracking resistance, storage stability under industrial conditions, additive compatibility with different bitumen sources, and long-term performance in actual pavements.
The findings nevertheless provide a scientific basis for further development of pomegranate peel extract as a natural bitumen antioxidant. The combination of reduced oxidation indicators, improved high-temperature grading, and an identified dosage range suggests that agricultural waste-derived compounds could contribute to future asphalt binder technologies, provided their processing requirements and long-term performance can be demonstrated at a practical scale.
By WPB
Pomegranate Peel Extract, Bitumen Aging, Natural Bitumen Antioxidant, Bio-Based Bitumen Additives, Oxidative Aging, Bitumen Rheology, PG 64, PG 70, Polyphenols, Asphalt Binder Modification, FTIR, SARA Analysis, Sustainable Asphalt, Agricultural Waste Recycling, Azarbaijan Shahid Madani University, Bitumen Technology
