Performance of eco-friendly geopolymer loadbearing bricks for thermally comfortable structures

Load-bearing masonry offers an eco-friendly alternative by reducing the use of cement and steel in the construction industry. However, bricks that satisfy structural requirements (high compressive strength and low water absorption) usually have high density and thermal conductivity, leading to greater energy demand for indoor heating and cooling. This study addresses that challenge by developing sustainable load-bearing bricks with improved thermal insulation. Bricks were fabricated and tested using ordinary concrete and geopolymer mixes based on industrial waste (fly ash and slag), incorporating lightweight coarse aggregate and air-entraining admixtures in various combinations. The compressive strength, water absorption, and thermal conductivity of each brick type were evaluated, and microstructural analysis (SEM/EDX) was performed. The results show that a fly ash-based geopolymer brick incorporating an air-entraining additive achieved the best balance between structural and thermal performance, exhibiting a compressive strength of 43 MPa, water absorption of 4%, and thermal conductivity of 0.7 W/m·K. These values satisfy load-bearing masonry requirements while providing lower thermal conductivity compared with typical conventional concrete bricks reported in the literature. The improved performance is attributed to the combined effect of geopolymer binder formation and the presence of distributed air pores that reduce heat transfer. These findings demonstrate that waste-derived geopolymer binders combined with lightweight aggregates and air-entraining admixtures provide a promising approach for producing high-performance, energy-efficient masonry units.