Synergetic effects of waste ceramic powder and low-grade calcined clay as precursors for the development of sustainable geopolymer binders

The decarbonization of the cement industry necessitates the development of alternative binders that utilize waste materials in accordance with circular economy principles. This study explores the alkaline activation of binary blends composed of waste ceramic powder (WCP), obtained from end-of-life brick materials, and low-grade calcined clay (LCC) derived from quarry overburden or clay-processing residues. While WCP offers an abundance but limited reactivity due to its high crystallinity, LCC provides a more amorphous aluminosilicate phase which is currently not sufficiently utilized. The results reveal that WCP alone undergoes flash setting accompanied by intense initial heat release, while the inclusion of LCC moderates the reaction rate and sustains reactivity over extended curing. Microstructural observations confirmed that LCC incorporation promoted continuous gel formation, refining the pore structure, and enhancing cohesion, leading to improved mechanical performance. Consequently, compressive strength improved from 18 MPa for pure WCP to nearly 40 MPa for the 50:50 blend after 90 days. The findings demonstrate that WCP/LCC blends effectively balance reactivity, workability, and strength, offering a viable low-carbon route for geopolymer binders’ production.