Characterization of organic–inorganic interfaces in silanized cementitious thin spray-on liners

Thin spray film formed by cementitious thin spray-on liner (TSL) has a wide range of applications in tunnel support. In order to improve the compatibility of the organic–inorganic interface in cementitious TSLs, silane coupling agents were used to modify the TSLs. In this study, four cementitious TSLs were configured, which were based on styrene-acrylic emulsions and vinyl acetate-ethylene copolymerized adhesive powders (EVA powders), respectively, and silanized with silane coupling agent of type KH-550. Macroscopically, the fresh flowability, compressive strength and flexural strength of TSLs were measured. Microscopic experiments were carried out with the aid of Leica microscope and scanning electron microscope. Thermogravimetric analysis (TGA), X-ray diffraction test (XRD) and low-field nuclear magnetic resonance test (NMR) were also carried out. The macroscopic results revealed that silanization decreased the fresh flowability of TSLs, but improved their compressive and flexural strengths. Microscopically, silanization significantly reduced polymer flocculation and improved the densification of the material. The silane and its derivatives bonded to the inorganic interface and captured polymer molecules, thereby promoting polymer film formation and inhibiting polymer agglomeration. The organic–inorganic interface after silanization exhibited higher strength. TGA showed that in styrene-acrylic emulsions modified cementitious TSL (STSL), silanization led to an increase in CH content, which enhanced the self-repair potential of STSL. In vinyl acetate-ethylene copolymerized adhesive powders modified cementitious TSL (VTSL), silanization consumed additional CH, which was attributed to the fact that the SiO₂ structure formed by polycondensation of silanes could pass through the polymer membrane in VTSL and react with the CH.

Graphical abstract