They mixed old rugs into asphalt: The result surprised everyone.

Researchers from North Carolina State University in the United States examined the effect of nylon fibers obtained from end‑of‑life tires on the durability of asphalt. The study, published in 2005 in the Textile Research Journal, showed that recycled fibers could increase asphalt's resistance to cracks that form under repeated loads.

Best Results Achieved with 12‑Millimeter Fibers

In the study, the adhesion properties of 15‑denier nylon fibers to asphalt were first evaluated. The critical embedment depth required for adequate adhesion was calculated to be 9.2 millimeters.

Subsequently, nylon fibers of 6 and 12 millimeters in length were incorporated into asphalt mixtures at volumetric proportions of 0.25 %, 0.5 %, and 1 %. The prepared specimens were subjected to laboratory tests to determine the fibers' effect on asphalt's mechanical properties.

Asphalt's Fracture Energy Increased by 85 %

The highest performance was achieved with the asphalt mix containing 12‑millimeter nylon fibers at a 1 % proportion. The fracture energy of this sample was found to be 85 % higher than that of asphalt without nylon fibers.

The findings indicate that nylon fibers recovered from carpet waste have the potential to increase resistance to fatigue cracking in asphalt. However, researchers noted that the study did not produce a directly ready‑to‑use, optimized asphalt mix. Additional evaluations are needed before the method can be applied in road construction.

Carpet Waste Is a Major Environmental Problem

According to data from the U.S. Environmental Protection Agency (EPA), the country generated about 3.4 million tons of carpet and rug waste in 2018. Only 310,000 tons of that amount were recycled. The recycling rate remained at 9.2%, while roughly 73% of the waste was sent to landfills.

The study presents a striking alternative for utilizing carpets that have reached the end of their useful life in road construction. However, the widespread adoption of this approach depends on confirming the long‑term performance of recycled fibers and their suitability for asphalt production processes.