Effect of silanization on mechanical properties and microstructure of thin spray-on liners with different polymer-cement ratios

Thin spray-on liner (TSL) is a polymer-modified cementitious composite. To enhance the compatibility of the organic-inorganic interface in TSLs and improve their performance, TSLs with three polymer-cement ratio gradients were treated with a silane coupling agent (SCA). We evaluated the impact of the polymer-cement ratio and silanization on the mechanical properties of TSLs. Additionally, we used a range of analytical techniques—nuclear magnetic resonance (NMR), Leica microscope, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD)—to assess the pore characteristics and hydration properties of the treated TSLs. The results indicated that silanization increased the compressive and flexural strength of TSLs, but the effect on toughness was not obvious. The excess polymer agglomerated into floccules, which were prone to plastic deformation, thus increasing the porosity of TSLs. Silanization facilitated the formation of a compact organic-inorganic interface transition zone. This prevented adhesion failure between the polymer and the cement material, and prevented plastic deformation of the floccules, resulting in a denser TSL. The newly formed polymer membrane-cement material composite bearing structure provided higher strength for TSL. Silanization inhibited the formation of pore throats, which increased resistance to the flow of CO2, H2O, and other substances. This restrained the growth of hydration products such as Ca(OH)2, CaCO3, and reduced the CH particle size. However, the formation of nanoparticles by silane polycondensation promoted the generation of calcium silicate hydrate.