Characterizing thermally and physico-mechanically an eco-friendly insulating brick made from gypsum and crushed sand rose stone using RSM and ANN

Due to the high energy consumption of the building industry, improving thermal insulation is essential. The choice of construction materials directly affects thermal comfort and energy efficiency. Increasing use of gypsum (G)-based products as thermal insulation in advanced building envelopes is prompting further research into their heating properties. This project aims to develop a novel bio-composite brick using locally available materials from southeastern Algeria that can withstand local environmental and climatic conditions. Specifically, locally sourced sand obtained from crushed sand rose (CSR) and traditional gypsum (G) were combined in an innovative way. The originality of this work lies in the integration of CSR as a functional aggregate combined with local gypsum, optimized through a multi-step RSM–ANN–GA approach. Two formulations were tested: C1 with 50 % CSR and 50 % plaster, and C2 with 60 % CSR and 40 % plaster. The best composition was predicted more accurately and consistently by the ANN/GA optimization than by the RSM/DF method: 40.2 % gypsum, 4.3 % CSR (3–8 mm), 58.8 % CSR (8–15 mm), and 35 % CSR (15–25 mm). This formulation achieved the most balanced performance in terms of mechanical strength and hygrothermal behavior. Furthermore, the composite brick containing 60 % CSR and 40 % G demonstrated better thermal insulation compared to commercial red bricks. This local composite brick effectively reduced indoor temperatures in hot regions, lowering them by 19°C after 30 min, and maintained a temperature difference of 19 °C at 120 min. Both bricks cooled to room temperature within 30 min, which is beneficial for buildings in arid and hot climates. • Eco-friendly brick made from 58 % sand rose and 42 % gypsum as optimal composition. • RSM and ANN models predict compressive strength with high accuracy (R² = 0.98). • Optimal mix yields 6.2 MPa strength and 0.35 W/m·K thermal conductivity. • Composite brick has 53 % lower thermal conductivity than standard red brick.