Radiative cooling potential of cementitious composites: Physical and chemical origins

Passive radiative cooling includes spontaneously cooling a structure by reflecting and emitting light through atmospheric window (8 μm–13 μm) into the cold universe. This paper involves a systematical study on maximizing the radiative properties of cementitious composites by optimizing constituents and microstructures. Relatively high hemispherical solar reflectance (82 ± 2) % and middle infrared (MIR) emissivity (87 ± 2) % were achieved simultaneously, allowing for an inner temperature drop of 12 °C in field test. Whiter surface, micro-magnitude pore size and TiO2 particle diameter all lead to higher reflectance in visible and near-infrared (VIS- NIR, 0.4 μm–2.5 μm) region. From the hydration products, complex infrared absorbance of O–H bonds yields low reflectance, while O–H, Si–O, Si–O–Si bonds stretching vibrations guarantee high emissivity. CaCO3, whether added as admixture or formed by carbonation, significantly increases the VIS reflectance. Both numerical simulation and field test demonstrate great potential of utilizing radiative cooling cementitious composites for building energy saving.