Alkali–thermal activation and physicochemical analysis of granite waste powder for one-part hybrid geopolymer cements

Alkali activation of granite waste is a sustainable route for low-cost powder-based binders, but low reactivity limits its use. This study enhances Completely Decomposed Granite (CDG) reactivity via alkali–thermal fusion to synthesize one-part Hybrid Geopolymer Powder (HGP). Raw CDG exhibited highly crystalline phases with Si, Al, and Ca concentrations of 3149.95, 501.48, and 9.26 ppb, respectively. Alkali fusion with minimal OPC improved dissolution to Si: 11026.71 ppb, Al: 2040.30 ppb, and Ca: 74.80 ppb, indicating effective activation. XRF analysis showed increased CaO and Na 2 O contents, promoting alkaline reaction pathways. XRD and FTIR confirmed partial amorphization and gel formation consistent with N–A–S–H and C–A–S–H networks, governing microstructure evolution. The activator type critically influenced performance; tap-water activation yielded limited geopolymerization and 16.75 MPa compressive strength at 28 days, whereas diluted water glass enhanced dissolution, gel formation, and matrix densification, reaching 48.82 MPa. Despite minor curing microcracks, the water–glass system was more cohesive. Environmental and sustainability considerations indicate that using CDG as precursor, reducing OPC content, and employing diluted alkali activators can improve resource efficiency and lower environmental impact. This study highlights powder activation, activator design, and sustainable valorization of granite waste in hybrid geopolymer binders.