Winter months reopen the same question anew every year: why do roadways and sidewalks "crack" so quickly during colder periods, so that potholes and unevenness appear on the asphalt after just a few cycles of ice and thawing? The problem is not merely aesthetic. Cracks and damage increase the risk of accidents for drivers, cyclists, and pedestrians, accelerate the deterioration of the base, and bring cities high bills for repairs that are often repeated from season to season.

Precisely at this intersection of safety, durability, and maintenance costs, a new idea appears that, at least according to laboratory results, could change the way asphalt "behaves" when temperatures drop below zero. A research team led by Prof. Elham Fini has developed an asphalt binder obtained from algae oil. In tests at temperatures below the freezing point, samples with algae showed less cracking compared to conventional petroleum-based binders.

Winter physics of asphalt: where the damage occurs

Most road surfaces are based on the same principle: a mixture of stone aggregate and sand is "held" together thanks to bitumen – a thick, sticky substance obtained by processing crude oil. Bitumen in asphalt has a dual role. On one hand, it binds aggregate particles and ensures strength, and on the other, it enables a certain elasticity, that is, the ability of the pavement to expand and contract as the temperature changes.

The problem arises when the temperature drops very quickly deep below zero. In such conditions, the bituminous binder can become more brittle and lose part of its flexibility, which increases the likelihood of micro-cracks under traffic load or under the influence of repeated freezing and thawing. Once cracks occur, water penetrates the pavement structure more easily. The water that subsequently freezes expands and further destroys the material, so damages over time turn into holes and upheavals – typical winter "breaking points" on roadways.

Binder from algae: a "rubberier" and more sustainable alternative

In a paper published in the journal ACS Sustainable Chemistry & Engineering, researchers present a so-called biobinder made from algae oil, conceived as a more sustainable and elastic alternative to part of the classic bituminous binder. According to the team's explanation, compounds obtained from algae could improve asphalt's resistance to moisture, increase flexibility, and encourage behavior resembling self-healing. In practice, this could mean a longer pavement lifespan and less need for expensive and frequent repairs.

This approach relies on earlier results from the same research direction: oil extracted from algae can be processed into a product that behaves "similarly to bitumen," but is more resistant and functional in certain temperature regimes. In the newer paper, researchers focused on a concrete question: which types of algae yield oils with the most favorable properties for asphalt, especially when it comes to low temperatures and rapid cooling.

Computer models and choice between four types of algae

To narrow down the choice, the team applied computer models to evaluate oil from four types of algae. The goal was to identify oils that can be processed into a binder compatible with the solid part of the asphalt mixture, while retaining functionality in freezing conditions. The oil of the freshwater green microalgae Haematococcus pluvialis stood out as the most promising candidate.

In simulations and assessments, oil of that species showed better resistance to permanent deformations under load similar to what happens on roads under the influence of traffic, as well as greater resistance to damage caused by the presence of moisture. For road construction, this is not a minor item: water and moisture, especially in combination with low temperatures, often accelerate asphalt degradation. If the binder tolerates moisture better and retains more elastic behavior, the pavement can remain in a state that is safer for traffic and more favorable for maintenance for longer.

Laboratory tests: traffic load and freezing cycles

After computer assessments, the researchers checked the formulations in laboratory demonstrations that mimicked a combination of traffic load and freezing cycles. In these tests, asphalt samples with a binder based on H. pluvialis showed, according to the authors, up to 70% better recovery from deformation compared to samples with a common binder obtained from crude oil.

Translated into everyday language, such a result suggests that the material could better "bounce back" after a load, i.e., more easily avoid permanent sagging and damage that over time become cracks. Behavior at low temperatures is precisely crucial for climates where winter brings sudden temperature drops and multiple consecutive episodes of freezing and thawing.

Climate impact: small replacement, large percentage in estimation

The paper also deals with the potential climate impact of replacing part of the petroleum binder with biobinder. Researchers estimate that replacing 1% of conventional, petroleum binder with an algae-based binder could reduce net carbon emissions associated with asphalt by 4.5%. In a scenario where the share of biobinder reached about 22%, asphalt could – according to their estimate – potentially become carbon neutral.

It is important to point out that these are estimates that depend on the assumptions of net emission calculations and the way carbon is calculated through the material's life cycle. However, the numbers clearly point to the logic of the research: even a partial replacement of material originating from fossil sources with a biomass-based alternative can have a measurable effect, especially if the technology were applied in large infrastructure projects where total binder consumption is substantial.

What the technology could mean for roads and sidewalks

Although these are laboratory results, the goal of the innovation is practical: to extend the lifespan of asphalt in conditions where frost and moisture accelerate degradation. In cities with pronounced winters, damage often does not appear gradually, but in waves – after sudden cold snaps and repeated ice cycles. Any reduction in cracks and permanent deformations could mean fewer emergency interventions, fewer temporary patches, and a more stable standard of maintenance.

Such a shift would also have a safety dimension. A pothole is not just an inconvenience that shakes the vehicle; it can cause damage to tires and suspension, loss of control, and falls for cyclists or pedestrians. If the binder proves more resistant in critical temperature conditions, it is reasonable to expect a lower risk associated with sudden surface deterioration – provided the results are confirmed outside the laboratory and in different types of asphalt mixtures.

From scientific paper to construction site: what still needs to be proven

For the innovation to cross the path from scientific paper to standard practice, it is customary that it must pass a series of additional checks: behavior in large batches and different asphalt mixture recipes, long-term exposure to UV radiation and oxidation, resistance to chemical influences (e.g., salts), and compatibility with existing industrial processes of mixing and installing asphalt.

There is also the economic aspect. Researchers describe the approach as a potential path toward high-efficiency, cost-acceptable, and sustainable infrastructure. However, the actual cost-benefit ratio largely depends on the costs of raw materials, processing, and logistics, as well as the pavement life cycle. In practice, "cheaper" is often not just the price of the material, but the total cost of maintenance over the years. If it were proven that biobinder reduces the need for repairs, the initial cost could be more easily justified.

Who is behind the research and how it was presented to the public

The paper on the algae-based biobinder was published on November 17, 2025, in the journal ACS Sustainable Chemistry & Engineering, and a broader summary of the results was publicly presented in a press release by the American Chemical Society (ACS) on December 15, 2025. The release highlights the focus on improving the durability of road and pedestrian surfaces in colder conditions, while simultaneously seeking more sustainable material solutions for infrastructure.

In the same context, it is stated that the authors of the research thanked the U.S. Department of Energy for funding, which is a common framework for projects linking material innovations, energy transition, and reducing environmental footprint.

ACS and the role of scientific journals in verifying claims

The American Chemical Society (ACS) operates as a non-profit organization founded in 1876 and chartered by the U.S. Congress. The role of the ACS in such topics is not conducting the research itself, but publishing and disseminating scientific results through peer-reviewed journals and communication channels like PressPacs releases. For the public, it is important to understand the difference: the press release is the entry point, while key details, methodology, and data are found in the scientific paper itself.

For now, the message the authors highlight comes down to two points: a biobinder obtained from algae oil shows potential for asphalt to become more resistant to cracking and permanent deformations in sub-zero conditions, while opening space for reducing net carbon emissions if part of the petroleum binder were replaced long-term with biomass-based material.