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'Supercool' Cement Keeps Roofs About 5°C Below Air Temperature in Midday Tests

The peer-reviewed material uses microstructured crystals to reflect sunlight, emitting heat to the sky for passive cooling.

Overview

  • Researchers report roof trials where the surface stayed roughly 5.4°C below ambient at about 38.4°C air temperature, while conventional concrete reached 59°C.
  • The cement’s optical design—ettringite crystals and microcavities—yields very high solar reflectance and radiative heat loss through the atmospheric window.
  • Stress testing indicates resistance to frost–thaw cycles, extra UV exposure and corrosive liquids, according to the study.
  • Lifecycle analyses suggest about 25% lower manufacturing CO2 and lifetime savings approaching three tonnes of CO2 per tonne of material in hot regions.
  • The team says the process can scale for roofs, façades and pavements; Spanish firm PhotoKrete is pursuing similar products and reports interest from international companies, with performance depending on clear skies and raising winter-use trade‑offs in temperate climates.