High‐performance geopolymer from brick wastes and metakaolin: Alkali treatment optimization, phase transformation, and property analysis

This study presents a cost‐effective and eco‐friendly method to produce aluminosilicate materials using red brick waste (RBW) and metakaolin (MK) as silica and alumina precursors. RBW was subjected to alkaline fusion to increase its dissolution for geopolymerization reaction. Response surface methodology was used to investigate the effect of NaOH concentration and fusion temperature on the leaching of silica and alumina from RBW. The microstructure of the alkali‐fused RBW was analyzed using x‐ray diffraction and Fourier‐transform infrared spectroscopy. Response surface methodology confirmed and revealed that higher NaOH concentration (14 M) and a temperature of 660°C favored solubilized phase development, resulting in 85% and 50% leached silica and alumina, respectively. These optimized parameters were then employed to prepare geopolymer materials with different proportions of alkali‐fused RBW and MK, using NaOH and Na2SiO3 as the alkaline solution. The elaborated geopolymer binders were characterized using various techniques such as x‐ray diffraction (DRX), Fourier‐transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal conductivity (λ), and fire resistance. The results showed that geopolymers containing 30 wt.% of alkali‐fused RBW exerted good mechanical and thermal insulation properties compared to conventional cement materials. However, excessive RBW addition causes negative effects. In addition, it was found that the blended geopolymers exhibited an increase in heat release rate (HRR), resulting in reduced fire resistance due to the presence of unreacted NaOH. Overall, these findings confirmed the potential sustainable use of RBW to partially replace MK in geopolymer as a material for building construction.