What if part of the answer to cleaner roads came from things we usually throw away—or sweep off the ground? This study finds that the source of that waste may matter more than expected. Road construction is moving toward replacing conventional asphalt binders with materials made from plants and waste.

Some alternatives have shown potential to cut greenhouse gas emissions by up to eighty percent, and some plant-based binders have even reported net-negative emissions. But changing the material inside asphalt can also change how the road behaves.

Pyrolysis turns biomass and non-recyclable waste into an oil with chemical similarities to fossil-fuel oils, yet its performance depends strongly on what was used to make it. The study compares oils made from pine needles, sawdust, rice straw, and municipal solid waste as distinct feedstock sources.

The central idea is like choosing a cooking oil for a recipe: oils may look interchangeable, but their ingredients can change the final result. Earlier studies often looked at one source at a time. Here, the comparison puts three plant sources and one municipal-waste source under the same conditions and at the same dosage, so the source itself can be compared more fairly.

The study compares different feedstocks under identical conditions and connects their characterization with the analysis of the resulting asphalt binders, rather than treating every waste-derived oil as identical. The binders were examined for their chemical makeup, heat behavior, ability to flow, stability while stored, and changes caused by aging.

Together, these checks connect the original material to the road binder it produces. Each modified binder replaced five percent of the base material with pyrolysis oil. Using the same amount for every source allowed the comparison to focus on differences in the oils, rather than differences in how much oil was added.

The five-percent level was chosen as a cautious starting point, because early binder tests commonly use low replacement levels to avoid making the material too soft before full road mixtures are studied. All of the modified binders became less stiff than the base binder, and they shifted toward more viscous behavior.

That could make them easier to work with and more flexible, but it can also reduce resistance to permanent deformation, especially at higher temperatures. The softening was greatest for the municipal-waste binder. The pine-needle binder stayed closest to the base material, making it the strongest match among the alternatives in this test.

A road binder also changes as it ages. The pine-needle binder showed the most favorable aging behavior, with slower hardening and better retention of its balance between stiffness and flow during service. Rice-straw binder showed the greatest tendency toward oxidation and hardening, with aging linked to greater stiffness, reduced mobility, and embrittlement.

Sawdust binder also showed greater aging-related deterioration, with accelerated hardening, increased viscosity, and greater risk of fatigue and thermal cracking as aging progresses. The study therefore identifies pine-needle bio-bitumen as the most promising modification for long-term performance, while noting that actual road mixtures still need further testing.

Pine-needle oil is identified as the most technically promising candidate for modifying asphalt and is recommended for further investigation in full road mixtures. Future work should test replacement levels from five percent upward to find the balance between workability, road behavior, and resistance to aging.

Across the comparison, performance depended strongly on the source material. Pine-needle bio-bitumen stayed closest to the base binder in chemical makeup, heat stability, flow behavior, storage stability, and resistance to aging.

The municipal-waste binder performed acceptably, but its contaminants need more checking before practical use. Rice-straw and sawdust oils showed more oxygen-related changes and greater sensitivity to aging. For someone driving on a future road, the message is simple: waste-derived asphalt may be possible, but the right waste matters.

Pine needles produced the most promising candidate here, offering a focused path toward more sustainable road materials. Not every waste-derived oil improves asphalt in the same way. Pine-needle oil stayed closest to ordinary asphalt across strength, heat, flexibility, and aging, pointing toward a more targeted route to lower-impact roads.