Improving Asphalt Recycling Using FT-IR Spectroscopy

Fact checked by" Jerome Workman, Jr.

Reclaimed asphalt (RA) is often used in many road maintenance and construction projects. A recent study demonstrated how Fourier transform infrared spectroscopy (FT-IR) can be used to analyze RA to ensure its efficacy for new asphalt mixtures.

According to a recent study published in Transportation Engineering, Fourier transform infrared (FT-IR) spectroscopy can be used to analyze the composition of reclaimed asphalt (RA) to ensure that it can be used in new asphalt mixtures (1).

RA is widely used in new asphalt mixes, boasting an impressive reuse rate of 85% (1). However, the variability in the aged and modified bitumen found in RA, along with potential hazardous polycyclic-aromatic hydrocarbon (PAH) contamination, poses significant challenges (1). Historically, PAH contamination has been a concern in Germany (1–3). This necessitates rigorous testing to ensure that recycled materials are safe and environmentally friendly.

black asphalt yellow markings | Image Credit: © Vitaly Krivosheev -

black asphalt yellow markings | Image Credit: © Vitaly Krivosheev -

Recently, a research team at the University of Kassel made a breakthrough in the recycling of RA, which is a crucial material in road maintenance and construction. Led by Jens Wetekam, the team developed a modified Fourier transform infrared spectroscopy (FT-IR) method, providing a rapid, efficient, and reliable way to analyze the composition of RA and ensure its safety and usability in new asphalt mixtures (1).

The traditional methods of analyzing RA, which include assessing bitumen content and grain size distribution, are insufficient for detecting many modern additives like waxes, rejuvenators, and rubber granulates. Moreover, they fail to identify hazardous PAHs adequately (1).

The newly developed FT-IR method developed by the research team overcomes these deficiencies. The study demonstrated that the FT-IR method developed significantly enhanced the ability to screen RA for various contaminants and additives (1). This technique involved a rapid extraction process that recovers the binder from a sample of granulated road construction material in approximately 20 min (1). Once that process is complete, the sample was then measured using attenuated total reflectance (ATR) FT-IR spectroscopy. The resulting absorption spectra allow for the identification of PAH contamination, with the method distinguishing between samples with PAH contents above and below the critical threshold of 25 mg/kg (1).

One of the key benefits of the FT-IR method was its ability to detect the presence of styrene-butadiene-styrene (SBS) modification and viscosity-changing organic additives. These components are increasingly used in modern asphalt mixtures, but identifying and managing them is paramount because they can complicate the recycling process if not properly identified and managed (1).

This research comes at a time when road maintenance is essential for economies to flourish. As road infrastructure ages, the efficient and safe recycling of materials becomes more critical, and not caring for it can result in damaging economic losses (1). The ability to quickly and accurately identify harmful substances and ensure the quality of RA directly impacts the sustainability and cost-effectiveness of road maintenance projects (1).

The potential of this method extends beyond Germany. As other countries grapple with similar issues related to road maintenance and recycling, the FT-IR technique could become a standard tool globally.

By leveraging FT-IR spectroscopy in this way, Wetekam and the team have opened new avenues for safer, more efficient road construction practices. The ongoing validation and potential regulatory integration of this method will be closely watched by industry experts and environmentalists alike as its impact on future infrastructure projects is monitored.


(1) Wetekam, J.; Mollenhauer, K. FTIR Spectroscopy Analysis Assessment of Reclaimed Asphalt at Asphalt Mixing Plants to Optimize the Recycling. Trans. Eng. 2024, 16, 100242. DOI: 10.1016/j.treng.2024.100242

(2) Taeger, D.; Koslitz, S.; Kafferlein, H. U.; et al. Exposure to Polycyclic Aromatic Hydrocarbons Assessed by Biomonitoring of Firefighters During Fire Operations in Germany. Int. J. Hyg. Environ. Health 2023, 248, 114110. DOI: 10.1016/j.ijheh.2023.114110

(3) Grmasha, R. A.; Stenger-Kovacs, C.; Al-sareji, O. J.; et al. Temporal and Spatial Distribution of Polycyclic Aromatic Hydrocarbons (PAHs) in the Danube River in Hungary. Sci. Rep. 2024, 14, 8318. DOI: 10.1038/s41598-024-58793-2

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