Precursor Compatibility in Multi-Source Alkali-Activated Materials: Coupled Dissolution, Elemental Competition, and Phase Selection

Combining multiple industrial waste streams as alkali-activated precursors provides compositional complementarity but also creates complex interactions that cannot be explained by bulk chemistry or final performance alone. This review examines precursor compatibility through three coupled processes: dissolution, elemental competition, and phase selection. Precursor reactivity is interpreted hierarchically in terms of bulk composition, potentially reactive composition, and the composition actually dissolved under specific reaction conditions. In multi-source systems, asynchronous release of Ca, Si, Al, Mg, and associated anions continuously modifies pore-solution chemistry, saturation states, nucleation, and interfacial transport. Dissolution therefore becomes mutually coupled, while released species compete for incorporation into binding gels and secondary phases. Their temporal availability, transport, and structural accommodation ultimately govern phase selection and spatial heterogeneity. Because increased strength or heat release alone is not a unique signature of chemical coupling, precursor compatibility should be established by linking changes in precursor-specific reaction kinetics with effective elemental supply and partitioning, phase evolution, and macroscopic response. This mechanism-based perspective reframes precursor compatibility as a conditional compatibility window, and shifts multi-source alkali-activated materials design from empirical precursor proportioning toward coordination of reaction time windows, elemental supply, and targeted phase formation under specified activator chemistry, pH, temperature, precursor proportion, curing conditions, and reaction time. Future studies should quantify time-resolved elemental balances and phase-competition boundaries and integrate them with reaction–transport models to identify robust compatibility windows under realistic precursor variability.