Interaction between microstructure and hygrothermal behavior of lightweight mortars containing glass waste powder.

Heat and moisture transfer through roof-layer materials strongly affect building energy use, yet conventional cementitious roof layers provide limited insulation and minimal vapor regulation. This study develops lightweight mortars incorporating recycled glass powder (RWGP) as a supplementary cementitious material and hydrogen peroxide (H 2 O 2 ) as a controlled foaming agent, and assesses how their engineered pore architecture governs coupled heat–moisture transport. Sixteen mixes were prepared under identical conditions and tested for thermal conductivity, thermal diffusivity, thermal effusivity, vapor-diffusion resistance, vapor permeability, and moisture-buffering value (MBV), together with porosity, effective porosity, and tortuosity. RWGP-driven pore refinement and H 2 O 2 -induced macrovoid formation generated stimuli-responsive pore networks that concurrently influenced thermal and hydric pathways. Thermal conductivity was significantly decreased relative to the reference mortar, while μ, WVTR, and MBV varied systematically with effective porosity and tortuosity, confirming that heat and vapor are governed by shared air-phase connectivity. A balanced composition was identified near 30% RWGP and 5% H 2 O 2 . These results provide a mechanistic basis for designing multifunctional, lower-carbon roof-layer mortars capable of improving insulation and moisture regulation within energy-efficient building envelopes.