Influence of lead glass sludge incorporation on the microstructure and engineering properties of fired clay bricks

The fired clay brick industry is a cornerstone of the global construction sector. However, the continuous depletion of natural clay reserves threatens the industry's long-term sustainability. Utilizing industrial solid wastes as partial clay substitutes is a recommended solution. Consequently, this study explores the safe integration of hazardous lead glass sludge (LGS) as an alternative to montmorillonitic clay at replacement levels of 8, 16, 24, and 32 wt%. The results reveal that LGS introduces amorphous silica, which triggers a bloating process. This expansion compensates for the shrinkage caused by clay dehydroxylation, thereby enhancing volume stability up to 900 °C. Furthermore, this foaming creates a highly porous structure, resulting in bricks with low bulk density and reduced thermal conductivity. While these effects increase with higher LGS content, they coincide with a reduction in compressive strength. Nevertheless, bricks containing 8–24 wt% LGS fired at temperatures up to 900 °C exceed minimum standard requirements. Acetic acid leaching tests confirmed that lead concentrations remain below toxicity limits, ensuring the environmental safety of the produced bricks. Ultimately, this strategy not only conserves raw clay but also provides a sustainable disposal method for hazardous LGS within the construction industry.