Lightweight waste-based gypsum composites for building temperature and moisture control using coal fly ash and plant fibers

Due to raw material shortages and waste management concerns, composite building materials made from industrial by-products have become a key component of tomorrow's construction sector. Herein, the synergetic effects of coal fly ash (CFA) and shot plant fibers (Alfa fibers – AF) on the thermophysical, mechanical and moisture-related properties of gypsum plaster were investigated. CFA was used as a partial gypsum substitute at a range of 0–80 wt%, while short AF were used as bio-aggregates ranging from 0 to 6 wt%. The developed composites presented bulk density, compressive strength, thermal conductivity and moisture buffering values between 934–1340 kg/m³, 1.38–6.98 MPa, 0.26–0.57 W/mK and 0.41–1.71 g/m²%RH, respectively. Experimental results proved the efficacy of CFA as hygrothermal optimizer, while AF served as hygroscopic agent and reinforcement to offset the compressive strength loss caused by generated porosity. Combining 50 wt% CFA with 6 wt% short AF resulted in a lightweight gypsum composite with enhanced hygrothermal capabilities that met compressive strength requirements (>2MPa). The proposed gypsum composite showed a good application prospect in passive thermal and humidity regulation in buildings.