Evolution of chloride binding and mechanical behavior in metakaolin-based geopolymer: Role of MgO-induced phase changes

Abstract

This work investigated the evolution patterns of amorphous phase and Mg-Al LDH crystals within MgO-modified metakaolin-based geopolymer (MMG) material from the perspectives of lattice structure interactions and chemical state evolution of oxygen atoms. Based on this, the role of MgO-induced phase changes in the chloride binding behavior and mechanical performance of MMG is revealed, thereby providing theoretical guidance for the design and application of geopolymer composites in marine environments. Results show that an increased LDH/amorphous phase ratio improves the chloride binding capacity of MMG material through the interlayer anion exchange and surface adsorption of Mg-Al LDH. Moreover, increasing LDH/amorphous phase ratio also contributes to the mechanical behavior of MMG via nano-nucleation, filling effect and Si-O-Mg bond formation. However, when this ratio surpasses 0.219, the pore structure development caused by the weakened binding effect of NASH gel becomes the dominant factor affecting the mechanical behavior, leading to a gradual decline in the compressive strength as the ratio increases. At an LDH/amorphous phase ratio of 0.306, MMG material achieves an optimal balance, exhibiting both excellent mechanical performance and chloride binding behavior.