Development of lightweight high-alumina cement mortars integrated with n-octadecane/expanded vermiculite for improving building energy efficiency

Phase change materials (PCMs) offer strong potential for reducing building energy demand. This study aims to develop lightweight structural mortars with improved indoor thermo-regulation by incorporating a form-stable PCM (FSPCM). The FSPCM was produced by impregnating expanded vermiculite (EV) with n-octadecane at a 40 wt% ratio. The reference mortar was prepared using EV as a lightweight aggregate at 25 wt% relative to cement. To obtain thermally enhanced composites, this EV fraction was replaced with FSPCM at substitution levels of 25–100 %. All mixtures were characterized to evaluate their physical, mechanical, and thermal performance. The mixture completely replaced with FSPCM showed the most significant improvements, achieving a thermal conductivity of 0.456 W/mK, density of 1.07 g/cm³ , and compressive strength of 8.81 MPa. DSC analysis of the FSPCM revealed melting and solidification temperatures of 25.76 and 25.42 °C, with latent heats of 100.4 and 99.5 J/g. Thermo-regulation tests confirmed effective reduction in indoor temperature fluctuations. A preliminary cost–performance evaluation, based on unit material prices and experimentally observed thermal benefits, indicates that FSPCM-integrated mortars may provide favorable life-cycle economics despite higher initial material costs. In conclusion, the EV/n-OC composites demonstrate strong potential as sustainable and energy-efficient building materials.