Researchers from the University of Salamanca have presented a prototype road surface that can reduce the risk of icing by using the natural heat of the ground. Unlike systems in which the surface is heated by electric cables or pipes circulating hot water, this prototype does not use an external energy source, relying solely on the temperature difference between the warmer soil layers and the cooled asphalt. In regions with moderately cold climates, this could become a practical alternative to chemicals and energy-intensive heating technologies.
Pilot sections with this road surface were built at a test site in the Province of Ávila, one of the coldest regions in central Spain. For the purposes of the experiment, two identical sections, a control section and an experimental section, were built, each measuring 2×1 m. The experimental section featured five vertical copper heat exchangers about 1 m long and a horizontal distribution grid about 5 cm below the surface. Copper was chosen for its high thermal conductivity (up to 385 W/m·K) and corrosion resistance.
The temperature was monitored over three winter months by DS18B20 IoT sensors placed at three depths: at the base of the heat exchangers, in the base layer and right under the asphalt. Data were transmitted via LoRaWAN every 10 minutes, with an average packet loss of less than 1.2%. The readings were compared to measurements from contact thermometers and thermal imagers, which made it possible to control accuracy and eliminate the influence of external factors, including solar radiation and local humidity.
The experiment showed a consistent increase in temperature in the geothermal section compared to the control section. At night, the difference averaged 1.5–2°C. In the most typical cases, the surface temperature of the control section dropped to –3°C, whereas temperatures in the experimental section remained between –0.8 and –1.2°C. This difference proves crucial in conditions when a thin ice film forms during minimal temperature deviations from zero. Thermal imaging data confirmed uniform heating across the entire area, indicating that the copper distribution grid operated properly.
A parallel simulation of heat transfer showed that the thermal front from the deep layer stabilizes within 10–12 hours. This time scale is consistent with theoretical estimates: with a depth of about 1 m and the typical thermal conductivity of wet soil, the characteristic time of heat diffusion is approximately half a day. Even with a low heat flux density (a few watts per square meter), this is enough to ensure a positive temperature gradient between the soil and the surface throughout the night.
According to preliminary calculations, the installation cost of this road surface totals about €75 per square meter, with virtually no operating costs: the system consumes no energy and requires no maintenance. With a service life of about 20 years, annual costs would amount to roughly €3.7 per square meter. It would be unproductive to compare this directly to the costs of road salt, since the use of reagents varies greatly depending on climatic conditions and the intensity of application. However, several studies have shown that the cumulative damage from salt application (infrastructure corrosion, vehicle damage and degradation of soil and water bodies) can reach $680–3,900 per ton. These figures reflect the general scale of the hidden costs involved in conventional winter maintenance.
The next stage of the researchers’ work involves full-scale testing: analyzing the corrosion resistance of copper in various soil types, simulating heat loss under traffic loads and evaluating the system’s effectiveness in harsher climatic conditions. It should be noted that the pilot section was not exposed to prolonged severe frosts or real-world traffic, and these factors remain key to transitioning from experimental development to a practical engineering solution.
