Retardation mechanism of alkali-activated slag by organo-silanes: From surface interaction to gel evolution

Abstract

The rapid setting of alkali-activated slag (AAS) poses a major barrier to its practical adoption. This study introduces a novel regulation strategy for the reaction of AAS by an organo-silane methyl trimethoxysilane (MTS). Comprehensive investigations reveal MTS achieves exceptional retardation through dual mechanisms: inhibiting slag dissolution and interfering with C-(N)-A-S-H gel formation. Calorimetry and in-situ LF-NMR confirm prolonged induction periods and delayed gel formation in AAS. Hydrolyzed MTS forms a hydrophobic siloxane layer on slag particles, acting as a barrier against alkaline attack and inhibiting the slag dissolution. Simultaneously, MTS incorporates into the gel structure, confirmed by FTIR and TG analysis, lowering gel hydrophilicity and elevating solution supersaturation, thereby hindering nucleation/growth of C-(N)-A-S-H. MTS outperforms conventional retarders (e.g., borax, ZnO) in efficiency at low dosages (≤4%), enabling tailored workability without compromising long-term performance. This work establishes organo-silanes as versatile molecular tools for reaction control in alkali-activated materials.