Rational application of nano-SiO2 in cement paste incorporated with silane: Counterbalancing and synergistic effects

Application of silane in cement-based materials has attracted increasing attentions due to positive benefits from the view of particle dispersion, wettability and durability. However, the accompanying negative problem of hydration retarding and strength reducing of silane remained unsolved. In this paper, starting from the enhancement effect of nano-silica, the influences of nano-silica and silane on flowability, setting time, strength development, wettability and water absorption of cement paste were studied systematically, and the hydration process, chemical composition and microstructure were evaluated by isothermal calorimetry, XRD, FT-IR, SEM and profilometer, respectively. Results shows that: nano-silica (NS) counterbalances the retarding effect of silane (IBTEO) on cement hydration and early age strength development, while the flowability of NS-cement paste was improved due to the dispersing effect of silane on NS; the synergistic enhancement effects of NS and IBTEO on water resistance of cement paste are well estimated by the remarkable 3D superhydrophobic behavior (water contact angle 153.5°) and lower water absorption rate (reduced by 70%); the hydrophobic mechanism of this hydrophobic cement specimen was summarized as the combination of lower surface free energy provided by IBTEO and more micro and nano roughness caused by NS.