Durability of alkali-activated materials with different C–S–H and N-A-S-H gels in acid and alkaline environment

This work explores the durability of alkali-activated materials exposed to acidic and alkaline environments to analyze and evaluate their applications. The alkali-activated materials of metakaolin and metakaolin-mine tailings were immersed in solutions of different pH values for 90 days, in which the durability of materials was studied. Characterizations include pH, FTIR, XRD, SEM and 29Si NMR measurements. It was found that the alkali-excited materials have good durability in an alkaline environment. A small amount of lye was diluted in the neutral solution, leading to a decrease in the amount of gel and a slight deterioration of the durability of the materials. Moreover, alkali-activated materials were corroded in acidic environments, leading to poor durability because hydrogen ions (H+) attacked N-A-S-H and C-A-S-H gels, and production of new sinjarite (CaCl2) mineral phases. This work provides a scientific reference value for the application of alkali-activated materials in daily environment.