Molecular-scale insights on structure-efficiency relationship of silane-based waterproofing agents

Abstract

While silane-based materials are widely used to improve the impermeability of concrete, the nano-scale interaction mechanismson the interfaces are still unclear. In this study, molecular simulations were employed to explore the inhibiting behaviors of three commonly-used alkoxysilanes(Aminopropyltriethoxysilane (APTES), ethyltriethoxysilane (ETES), and γ-(methylpropyleneoxy)propyltrimethoxysilane (MPS)) on the transport of aggressive ions and water throughout a nano-pore of calcium silicate hydrates (C-S-H). The results show that during the penetration process of silane-doped systems, both water and ions exhibit a low density state and a longitudinal stratification owing to the barrier effect of silanes, where the ranking was APTES < ETES < MPS. The order can be explained by differences in the molecular structure. MPS demonstrates the best inhibiting effect because it possesses maximum hydrophobic groups. For APTES and ETES with similar molecular weights, the drag effect of amino groups, results in water molecules being more likely to penetrate the interface area and escape, causing a weaker inhibiting effect in APTES. The mechanisms interpreted in this work may shed new light on the molecular design of silane-based waterproofing agents.