Macroscopic and microscopic characteristics of nanosilica sol-based composite grout in sealing fractured argillaceous rock: A comparative study with silica sol and cement slurry

Argillaceous surrounding rock is prone to weakening when exposed to water, which can cause significant long-term deformations and instability in roadways. This paper focuses on a high-injectability, high-strength nanosilica sol-based composite grout, characterizing its sealing patterns at both the macroscopic and microscopic levels within multilevel porous argillaceous rock bodies. It also explores the microscopic structural interactions at the grout-rock interface. Additionally, the paper compares the performance of this composite grout with traditional silica sol and cement grout, providing initial insights into the anti-seepage reinforcement mechanism of the composite grout when used in grouting argillaceous soft rock. The research results show that, for composite grouting (1) The porosity and sealing of the grout-rock cementitious body decrease with increasing particle size of the rock blocks, with a minimum permeability coefficient of 2.34 × 10⁻⁸ cm/s; (2) The presence and distribution pattern of multi-level pores of grout in rock fractures can be evaluated using the T2 spectrum of nuclear magnetic resonance (NMR). The pore volume of the cementitious body is mainly provided by large pores <100 ms, and the composite grout has a good sealing effect on the matrix system of the argillaceous rock. (3) There is a dense transition area at the grout-rock interface, formed by the accumulation of nano-materials such as aluminate cement hydration-formed aluminate gel and silica sol. On the grout-rock interface, aluminate gel nucleates on nano-SiO₂, continuously precipitating, aggregating, and cross-linking on the surface of silica particles to form a dense gel, filling the cavities at the grout-rock interface and increasing structural density. The research findings aim to provide theoretical support and experimental research basis for the practical application of composite grout in anti-seepage reinforcement engineering of argillaceous soft rock at the site.