Mechanical, microstructural, and chloride ion penetration data of metakaolin specimens

This investigation reveals a critical “performance window” for NaOH molarity (8–16 M) in metakaolin-based geopolymer concrete (MKGC) through an integrated analysis of mechanical properties, chloride transport, and multi-scale microstructure. Within this window, an optimal concentration of 14 M facilitates a synergistic regime in which geopolymerization produces a gel that is both dense (enhancing physical protection) and chemically active for chloride binding. This results in a significantly reduced chloride diffusion coefficient of 4.19 × 10⁻¹² m²/s. Deviations from this window lead to a decoupling of the synergistic effect: lower alkalinity yields a porous microstructure, whereas higher alkalinity inhibits effective chemical binding despite ongoing pore refinement.