Intrinsic Sulfuric Acid Resistance of C-(N)-A-S-H and N-A-S-H Gels Produced by Alkali-Activation of Synthetic Calcium Aluminosilicate Precursors

This study investigates the decomposition of alkali-activated materials (AAMs) in sulfuric acid solution. Four sodium-containing calcium aluminium-substituted silicate hydrate (C-(N)-A-S-H) and aluminosilicate hydrate (N-A-S-H) gels with designed Ca/Si and Si/Al ratios are produced with synthetic calcium aluminosilicate powders. The formation of additional calcium products in Ca-rich and Al-sufficient sample is likely helpful to retard the attack of sulfuric acid on the C-(N)-A-S-H/N-A-S-H gels. The SiO bond strength of N-A-S-H gel appears weaker than that of C-(N)-A-S-H gel. The calcium in the gels prevents the leaching of silicon from gels. The length of silicon chains in the C-(N)-A-S-H gel increases with increased Si/Al ratio while exposure to acid solution. The chain length of the N-A-S-H gel increases with reduced Si/Al ratio. C-(N)-A-S-H gels show a higher resistance to leaching than N-A-S-H gel, while the latter has a high resistance to depolymerization under acid attack. This study provides a basic route to understand the effect of AAMs composition on acid resistance.