Molecular investigation on interfacial toughening between silane coupling agent treated glass fiber and cement

Abstract

Silane coupling agents (SCAs) are widely used as adhesion promoters to tightly bond glass fiber (GF) and cement matrix (CM) for developing sustainable and high-performance glass fiber-reinforced cementitious (GFRC) composites. This study uses molecular dynamics (MD) simulation to examine the effect of 3-aminopropyltriethoxysilane (APS) on CM/GF interfacial properties. Pure cement and nine cement models bonded to APS-modified GF with APS concentrations of 0.00%, 12.50%, 25.00%, 37.50%, 50.00%, 62.50%, 75.00%, 87.50%, and 100.00% are constructed. It is shown that pure CSH system experiences interfacial delamination. With increasing APS from 0.00% to 37.50%, the failure mode transits from interfacial delamination to CSH delamination, and with increasing APS to 100.00%, it transits to interfacial delamination. Meanwhile, it is measured that with increasing APS from 0.00% to 37.50%, the tensile strength increases from 0.48 to 0.58 GPa and the adhesion energy increases from 0.71 to 0.90 J⋅m−2. Comparatively, with increasing APS to 100.00%, the tensile strength decreases to 0.26 GPa, and the adhesion energy decreases to 0.23 J⋅m−2. Moreover, the interfacial structure and chemical bond analysis demonstrate that with increasing APS from 0.00% to 37.50%, the peak of H2O molecules decreases, which denotes stronger interfacial bonding. With increasing APS from 37.50% to 100.00%, the peak of the H2O molecules increases, which induces low interfacial bonding. These findings provide a basis for optimizing APS concentrations for specific performance enhancements of GFRC materials.