Chemical and physical effects of the addition of thermochromic VO₂ particles to cement

This work aims to deepen the knowledge of systems formed by cement and thermochromic vanadium dioxide particles. Cement paste specimens with 9 % addition of monoclinic VO₂ particles show a significant delay of the hydration at early ages with respect to plain cement specimens, seemingly due to the partial inhibition of hydrates precipitation during the first 24 h of reaction. Upon further hydration, a re-activation of the hydration reactions gives rise to a higher mechanical strength and a more refined pore structure in the paste with VO₂ addition at 28 days, attributed to the enhanced formation of C–S–H. The stability of the VO₂ particles within the matrix is confirmed along the hydration process and provides the cement paste with the associated thermochromic behavior that is demonstrated by a change in the reflection in the near infrared wavelength range upon cooling from 70 °C. The results confirm the viability of producing VO₂-based thermochromic cementitious materials for building envelopes. The next steps in their development should target the enhancement of the solar reflectance modulation in order to produce a significant impact in the energy efficiency of buildings and the urban overheating effect.