This work evaluates the radiative cooling potential of cement for the use in photonic metaconcrete, capable of energy savings and reduction of CO2 emissions. In particular, we present a comparative study of the optical and radiative properties of primary clinker products (alite and belite), as well as typical sulfate additives such as CaSO4 and gypsum, across the ultraviolet, visible, and infrared ranges. The dielectric response, emissivity and reflectance were obtained using first-principles calculations, specifically density functional theory (DFT), together with the GW and the Bethe–Salpeter equation (BSE) methods. This advanced computational approach identified strongly anisotropic excitons within the electronic band gaps of the cement phases. Our findings revealed that both oxygen and silicon or oxygen and sulfur bonds play a central role in thermal emission within the atmospheric transparency window. The combination of selective emissivity and high solar reflectivity suggests that cement-based nanocomposites are promising candidates for radiative cooling applications. Furthermore, the reflectance measurements indicate an electronic band gap of 5.24 eV. Overall, this work advances our understanding of the optical and thermal behaviour of cementitious materials, and provides insights into the design of energy-efficient photonic concrete composites.