RELUM: Innovative reflective pavements to reduce the urban heat island effect

Global warming and urban growth have intensified the phenomenon known as urban heat islands, which cause higher temperatures in cities compared to rural areas. This occurs because materials such as asphalt and concrete have a high capacity to absorb and retain heat. Urban infrastructure materials absorb more solar radiation and release heat slowly, thereby raising the ambient temperature. This phenomenon has negative consequences, as it affects thermal comfort, increases energy consumption, and deteriorates air quality in cities. This situation, together with the growing concern of public authorities to mitigate this effect, has driven research and innovation to develop solutions that foster more sustainable and healthier environments. RELUM was conceived as an innovative response to this challenge.

The project’s objectives were, firstly, to investigate how materials and their combinations in hot asphalt mixtures influence solar reflectance and the surface temperature reached by the pavement as a result of solar radiation. Secondly, to design pavements with high solar reflectance, that is, with a strong ability to reflect rather than absorb solar radiation. Higher solar reflectance reduces the accumulation of heat in buildings and pavements, thus contributing to lowering the urban heat island effect.

Within the framework of the RELUM project, the potential of reflective pavements has been demonstrated, particularly, ultrafine mixtures with different combinations of aggregates and pigments. The surface temperatures of these materials exposed to sunlight were measured at different times of the year (on very hot, very cold, and mild days) to observe their behaviour under real conditions.

The project revealed that lighter mixtures, made with limestone aggregates, synthetic bitumen, and titanium dioxide pigment, achieved the highest reflectance, reaching 57%, whereas darker mixtures, made with porphyry aggregates and conventional bitumen, showed the lowest reflectance, around 8%. A maximum temperature difference of 22.7°C was recorded between them.

Impact

The results obtained through the project have enabled progress in the development of new reflective pavements that reduce heat absorption and retention, helping to mitigate the urban heat island effect. By lowering ambient temperature, these pavements promote urban sustainability and improve citizens’ well-being.

Budget and Funding

The project received a total budget of €148,580 under the Spanish State Plan for Scientific, Technical and Innovation Research 2021–2023 (TED2021-132077B-I00). It has had a duration of two years (November 2022 – December 2024).