Study of adhesion properties and mechanism of sodium silicate binder reinforced with silicate fume

In this study, the effect of different amounts of silica fume additive on the bonding strength of sodium silicate binder, over time, was studied. It has been concluded that silica fume can improve the bonding strength and humidity resistance of sodium silicate bonded sand. The microscopic morphology of the adhesive film was examined by scanning electron microscopy, and the functional group changes of the polymerised adhesive were analysed by Fourier-transform infrared (FT-IR) spectroscopy. In addition, the hardening mechanism, between the sodium silicate binder and silica fume on the sand surface, and the hydration reaction mechanism, after polymerisation, were investigated using first-principles calculations in the CASTEP program based on density functional theory (DFT). It was found that silica fume enhances the binding energy of the binder by enhancing the degree of polymerisation, while subsequent hydration of the hardened binder is a spontaneous reaction. After the sodium silicate binder hardens, the water molecules are adsorbed by unpolymerised –OH and Na+; these water molecules destroy the -Si-O-Si bonds to depolymerise the sodium silicate bonded network. This research provides important theoretical support for improving or even eliminating the hygroscopic properties of sodium-silicate-bonded sand during casting.