Finding scalable, cost-effective and environmentally safe solutions for Passive Daytime Radiative Cooling (PDRC) is essential for addressing energy and climate challenges. This study demonstrates the feasibility of achieving PDRC using only cement-based compounds, without the need for additional whitening agents or other additives. Unlike previous approaches that rely on external additives, the proposed solution leverages two fundamental cement phases—portlandite and tobermorite—offering a scalable and low-impact alternative. The research evaluates the radiative cooling potential of these phases, along with two widely used cements—white cement (WC) and ordinary Portland cement (OPC), by analyzing and comparing their homogenized complex permittivities, derived using the Kramers-Kronig (KK) method. Simulations were conducted to assess the cooling power over one year across three different climates using actual meteorological data. The portlandite exhibits positive Pcool, maintaining a temperature equal to or below the ambient temperature more than 90 % of the time in dry desert and warm temperate locations. Indoor controlled measurements results reveal that portlandite (CH) may exhibit temperatures 15 °C lower than OPC and 5 °C lower than WC.

The research presented in this paper has been supported by funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 64450 (MIRACLE project, more information available at www.miracle-concrete.eu) from the EU Commission. Additionally, this work has received financial support from the projects TED2021-132074B-C31, TED2021-132074B-C32 and TED2021-132074B-C33, funded by MCIN/AEI/10.13039/501100011033, and the European Union NextGenerationEU/PRTR and from the projects PID2022-137845NB-C21, PID2022-137845NB-C22 funded by MCIN/AEI/10.13039/501100011033/and by FEDER Una manera de hacer Europa.

Peer reviewed