According to WPB, researchers from Iran University of Science and Technology and Khayyam University have achieved a 295% increase in the laboratory fatigue life of hot mix asphalt by replacing part of its natural aggregates with recycled polyethylene terephthalate (PET) obtained from discarded plastic bottles. The findings, published on November 9, 2026, also showed a 57% improvement in creep resistance under a different mixture formulation, highlighting the potential of recycled plastic aggregates to improve asphalt performance.
The research introduces an alternative approach to incorporating plastic waste into asphalt mixtures. Rather than using PET to modify petroleum bitumen directly, the researchers processed discarded plastic bottles into aggregate-like particles and used them to replace selected portions of natural stone aggregates. This method preserves the distinction between the bitumen binder and the aggregate structure of the asphalt mixture.
The study focused on the effects of PET particle size and replacement percentage on the mechanical performance of hot mix asphalt. Recycled PET particles were processed and separated into standardized size fractions to allow comparisons with natural limestone aggregates. The researchers used a dry mixing process, incorporating the recycled particles into the asphalt mixture as a partial aggregate substitute.
The experimental program initially replaced 10% of natural aggregates by volume with recycled PET across five particle-size ranges, extending from 0.3 millimeters or smaller to 19 millimeters. The results were then used to identify the most effective size range and determine suitable replacement levels for further testing.
The strongest overall performance was obtained with PET particles measuring between 4.75 and 12.5 millimeters. Within this range, replacing 16% of natural aggregates by volume increased the fatigue life of the asphalt mixture by 295% compared with the reference mixture. This represents a laboratory fatigue life approximately 3.95 times that of the conventional mixture under the tested conditions.
Fatigue resistance is a critical property of asphalt pavement because repeated vehicle loading gradually damages the material and contributes to the formation of cracks. The substantial increase recorded in the study indicates that an appropriately designed PET-containing mixture can withstand considerably more repeated loading cycles before reaching the laboratory fatigue failure criterion.
A separate mixture containing 18% recycled PET aggregate by volume achieved a 57% increase in creep resistance. The same replacement level also reduced moisture susceptibility by 7%, demonstrating improvements in resistance to deformation and moisture-related deterioration under the investigated test conditions.
These results are particularly significant because the optimum replacement percentage was not identical for every performance indicator. The 295% fatigue-life improvement was recorded at 16% PET replacement, while the 57% creep-resistance increase was associated with 18% replacement. Both results were obtained using the selected 4.75–12.5 millimeter particle-size range.
To examine resistance to deformation under repeated loading, the researchers conducted dynamic creep tests at 40°C, measuring flow number and permanent deformation. Moisture susceptibility and indirect tensile fatigue performance were evaluated at 25°C. These laboratory procedures provided a basis for comparing the behavior of conventional asphalt mixtures with those containing different proportions of recycled PET.
The researchers also evaluated the interaction between PET particles and the bitumen binder. At moderate to elevated temperatures, recycled PET demonstrated stronger interfacial adhesion with bitumen than the limestone aggregates used for comparison. This finding is relevant to the mechanical behavior of asphalt mixtures because the interface between binder and aggregates plays an important role in distributing stresses and maintaining structural integrity.
Additional aggregate tests, including Los Angeles abrasion and aggregate impact value assessments, indicated favorable mechanical characteristics for the processed PET particles compared with the limestone materials examined. The findings support the use of suitably prepared recycled PET as a functional component within the aggregate skeleton rather than simply as a waste material added to asphalt.
Particle size emerged as a major factor influencing performance. The study demonstrated that the behavior of recycled PET aggregates depends on both their dimensions and the proportion used in the mixture. Selecting an appropriate particle-size distribution is therefore important for achieving improvements in fatigue resistance, deformation resistance, and moisture performance simultaneously.
The environmental relevance of the research lies in creating an additional application for post-consumer plastic bottles and reducing the quantity of newly extracted natural aggregates required in asphalt production. By partially replacing stone aggregates, the technology could contribute to more efficient use of recycled materials in road construction. The study's reported percentage improvements concern mechanical performance and should not be interpreted as quantified reductions in carbon emissions.
For the bitumen industry, this development represents an important distinction from conventional polymer modification technologies. Petroleum bitumen remains the binder in the asphalt mixture, while recycled PET replaces part of the mineral aggregates. The approach therefore introduces a potential innovation in asphalt mixture design without requiring the complete replacement of petroleum-derived bitumen.
The findings are also relevant to asphalt producers and road construction companies seeking to incorporate recycled materials while maintaining suitable engineering properties. The reported improvements in fatigue life and creep resistance demonstrate the importance of selecting appropriate particle sizes and replacement percentages rather than treating recycled plastic as a uniform additive.
The results were obtained through controlled laboratory experiments, not through long-term monitoring of an operating road. Consequently, the 295% increase in fatigue life describes the performance of the tested asphalt specimens and does not represent a demonstrated 295% extension of pavement service life in real traffic conditions. Field evaluation remains the next important step in assessing the technology's practical performance.
The research highlights a promising application for recycled PET in asphalt engineering. By replacing a carefully selected portion of natural aggregates with particles produced from discarded plastic bottles, Iranian researchers have demonstrated substantial improvements in laboratory fatigue and deformation resistance. The findings provide a technical foundation for developing recycled-aggregate asphalt mixtures and expanding the use of plastic waste in future road construction projects.
By WPB
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