Mortar composites incorporating VO2/MWCNT solid–solid nanophase change material for passive indoor temperature regulation

Abstract

Phase change materials (PCMs) have emerged as promising materials for improving the thermal performance of building envelopes. In this study, a solid–solid nanophase change material (nanoPCM) composed of vanadium dioxide (VO 2 ) and multiwalled carbon nanotubes (MWCNTs) was synthesized and incorporated into cement mortar at contents ranging from 0.5 to 3 wt%. The effects of nanoPCM incorporation on hydration behavior, microstructure, compressive strength, thermophysical properties (specific heat capacity, thermal conductivity, diffusivity and effusivity), thermal regulation capacity and energy saving were investigated. The results revealed a synergistic interaction between VO 2 and MWCNTs, reducing the phase transition temperature (Tc) from 72.41 °C to 63.73 °C while increasing thermal conductivity by approximately 3.5 times. The incorporation of nanoPCM slightly increased mortar density and improved long-term compressive strength, with a maximum increase of 24.5% observed at 1 wt% nanoPCM addition. Hydration calorimetry revealed that nanoPCM delayed early-age hydration kinetics without suppressing the overall hydration process. In the mortar composites, nanoPCM incorporation reduced thermal conductivity, diffusivity and effusivity with a slight decrease in the specific heat capacity, resulting in enhanced thermal inertia and delayed heat transfer. Thermal regulation tests confirmed a reduction in temperature fluctuations, while building energy simulations demonstrated annual energy savings of up to 2.23%, depending on climatic conditions. These findings demonstrate that tailoring the thermophysical properties of cementitious materials through VO 2 /MWCNT solid–solid nanoPCM represents an effective strategy for improving passive indoor temperature regulation and reducing building energy demand without compromising mechanical performance.