Cement paint coupling radiation and evaporation against urban heat island

As urban heat island (UHI) effects intensify, radiative cooling (RC) and evaporative cooling are emerging as highly promising strategies for building-scale thermal management, yet durable, self-curing, cementitious systems that integrate multiple cooling modes remain in the early stage. Recent research published in Science by Li and his colleagues provides an innovative solution. They report a cementitious cooling paint, cement-cooling paint (CCP)-30, that ingeniously integrates radiative and evaporative cooling mechanisms within a durable cementitious matrix. Compared to commercial paints, this paint effectively overcomes the limitations of conventional technologies in hot-humid climates and building facade applications. This work presents a highly promising and practical solution for mitigating UHIs in megacities, holding significant importance for global architectural energy conservation.

With the continuous advancement of urbanization, a large number of buildings and roads have replaced the natural surface. Due to high solar absorption and low reflectance, common urban building materials such as concrete and asphalt absorb a large amount of solar heat, intensifying the UHI effect. Superimposed climate warming aggravates the UHI effect, leading to serious thermal stress of buildings and outdoor facilities1 and ultimately compromising human health.2 Transformative passive cooling has therefore become imperative to curb the increasingly serious UHI phenomenon.

Although radiative passive cooling technology, which dissipates heat through the atmospheric window, shows obvious cooling performance in dry and clear climatic conditions, it degrades significantly in high-humidity and cloudy environments (e.g., Singapore). Furthermore, its directional nature significantly limits cooling efficiency on surfaces such as vertical building facades.3 Evaporative cooling, utilizing water’s high latent heat (∼2,256 J/g), provides a non-directional cooling mechanism that can overcome the limitations of RC. However, the current multilayer hydrogels used for evaporation suffer from swelling, poor adhesion, and structural degradation during wet-dry cycles, hindering long-term reliability. Recent metagel designs integrate multiple cooling strategies but still face challenges with scalability and strength.4 Thus, developing a paintable, durable, and scalable fabricating synergistic material that integrates radiative and evaporative cooling is desirable to overcome their complementary limitations, yet it remains an enormous challenge and significant goal.

In a milestone work recently published in Science,5 Professor Hong Li’s group from Nanyang Technological University and his colleagues designed a CCP with advanced thermal-optical and mass transfer properties, significantly enhancing the passive cooling performance (Figures 1A and 1B). In detail, a calcium silicate hydrate (C-S-H) network is generated by taking advantage of the hydration of cement powder, yielding a uniform and interconnected micrometer-sized porous structure.