From Waste Powder Characteristics to Geopolymer and Alkali-Activated Material Performance: Reactivity, Processing, and Circular-Economy Pathways

Waste-derived geopolymers and alkali-activated materials are often compared through bulk oxide composition and compressive strength, although precursor reactivity also depends on the physical and mineralogical characteristics of the powder. This critical review examines how phase accessibility, particle-size distribution, specific surface area, morphology, porosity, loss on ignition, and soluble or potentially harmful constituents influence processing, reaction products, and performance. The evidence compiled for nine representative waste-powder classes suggests that total SiO2 and Al2O3 contents are insufficient predictors of reactivity because powders with similar bulk compositions may differ markedly in amorphous content, accessible surface, liquid demand, and dissolution behavior. A comparative profile summarizes quantitative powder characteristics and the advantages and limitations of each precursor class. The review also identifies the functional roles of waste powders as network formers, calcium-rich hardening components, silica-rich modifiers, fillers, internal alkali sources, or contaminant-bearing constituents requiring stabilization. Based on these relationships, the review proposes a powder-centered qualification framework, a decision-gate sequence for industrial deployment, and a minimum reporting dataset linking precursor characteristics with formulation, processing, durability, and environmental evidence. Industrial translation requires performance-based acceptance windows, safer activation, long-term durability and leaching evidence, and region-specific life-cycle, exergy, and techno-economic assessments to determine whether these powder functions can create commercial value at scale.