Tailoring Water-Resistant Hybrid Geopolymers with triethoxyvinylsilane and Hexadecyl-trimethoxy-silane: A Comparative Study

The development of water-resistant geopolymer systems is crucial for extending the durability of alkali-activated binders in humid and aggressive environments. In this study, metakaolin-based geopolymers were modified with triethoxyvinylsilane (TEVS) and hexadecyltrimethoxysilane (HTS) to impart hydrophobic functionality at the matrix level. The reference geopolymer exhibited a low contact angle of 30°, confirming its hydrophilic surface. Incorporation of TEVS and HTS significantly improved wettability resistance, producing contact angles of 135° and 128%, respectively, attributable to vinyl-silane grafting and long-chain alkyl silane functionality. FTIR spectra confirmed reduced O-H stretching intensity (3430 cm⁻¹) alongside the emergence of Si-C and C-H vibrational bands, validating the successful incorporation of hydrophobic groups. SEM micrographs revealed improved matrix densification and reduced pore connectivity, particularly in TEVS-modified samples, while EDX spectra indicated carbon enrichment from 2.7% in the control to 28% and 25% in TEVS and HTS composites, respectively. Water absorption testing further highlighted the durability enhancement, with TEVS- and HTS-modified specimens restricting uptake to 0.34% and 0.40% after 28 days, compared to 1.5% in the control. The comparative analysis demonstrates that TEVS yields slightly superior hydrophobic performance due to stronger interfacial crosslinking, whereas HTS provides long-chain barrier effects. These findings establish silane-modified geopolymers as multifunctional composites with enhanced moisture durability, suitable for applications in marine infrastructure, wastewater systems, and chemically aggressive service environments.