Gradient cementitious composites with durable radiative cooling and liquid-repellent surfaces for building envelopes

Passive daytime radiative cooling (PDRC) offers an energy-free approach to cut building cooling demands, yet conventional coating-based systems suffer from interfacial instability, mechanical damage, and contamination-triggered performance degradation. Herein we propose a phase-separation-assisted strategy to build continuous functional gradients intrinsically inside cementitious bodies via one-step casting-and-curing. The gradient originates from coupled influences: density-driven redistribution, hydrophilic-hydrophobic incompatibility, polycarboxylate-superplasticizer-modulated particle dispersion and slurry rheology, plus gradual immobilization during cement hydration and setting. Such effects concentrate PVDF-HFP and hydrophobic fumed silica within the porous upper layer, with a denser cement-rich supporting region formed beneath. This one-step route avoids sequential deposition/lamination and removes the failure-prone discrete coating-substrate interface, yielding a monolithic material (GCRM) integrating radiative-cooling, liquid-repellent, and mechanical performances. GCRM delivers a solar reflectance of 90.28 ± 0.14% and an infrared emissivity of 97.94 ± 0.27%. Outdoor rooftop-model tests yield a maximum daytime internal-air-temperature reduction of 2.6 °C versus bare wooden roofs, verifying its solar-heat-suppressing capacity. Owing to depth-distributed functional components, surface abrasion induces gradual rather than abrupt decay of water repellency; GCRM maintains superhydrophobicity after 300 abrasion cycles and preserves favourable optical properties after 28-week liquid immersion and 1-month UV exposure. Crushed end-of-life GCRM can serve as functional fillers for cascade reuse. Nevertheless, a full life-cycle assessment is absent. Its net environmental benefit still requires comprehensive evaluation covering material production, operational energy savings, reprocessing, fluorinated-constituent release, and final disposal.