Fresh to hardened evolution of one-part sodium carbonate-slaked lime activated materials: Dual role of steel slag and decoupling effect of activator composition

This study clarifies the fresh to hardened mechanisms of one-part sodium carbonate-slaked lime activated material (CLAM). Fresh rheology, hydration kinetics, zeta potential, ion concentration, phase assemblage, thermal response and morphology were examined. Steel slag played a dual regulatory role: higher replacement weakened the fresh particle-gel network and reduced yield stress and thixotropic rebuilding, whereas moderate incorporation may promote sustained product formation by supplying additional Ca-bearing phases, facilitating heterogeneous nucleation, and improving interparticle filling and matrix development. This favored the balanced coexistence of C-(A)-S-H-type gel, calcite-rich products, and residual Ca-silicate phases, while excessive replacement diluted the reactive slag fraction and disrupted gel continuity. The activator composition induced rheological decoupling: it strengthened the low-shear skeleton via Ca 2+ /OH - assisted dissolution, electrostatic screening, and gel bridging, while simultaneously reducing the equivalent plastic viscosity of the paste, potentially through changes in particle interactions and post-breakdown rearrangement. The activator composition also redirected the reaction pathway: under sodium-carbonate-rich conditions, the mixture showed high Na + and dissolved Al, low dissolved Si, delayed acceleration, high cumulative heat release, preferential carbonate accumulation, and delayed continuous Ca-rich gel development. Insufficient activator mainly suppressed chemical activation and precursor dissolution, whereas excessive water caused physical dilution and weakened reaction-product connectivity. These findings reveal that the fresh to hardened mechanisms of one-part CLAM are jointly governed by rheological structuration, hydration kinetics, solution chemistry, and the competitive balance between gel formation and carbonate precipitation.