Permeable crystalline materials and nano-SiO₂ modified cement grout performance and anti-seepage mechanism

In order to improve the impermeability of tunnel synchronous grouting materials, the impacts of water-cement ratio (W/C), PCS dosage, XYPEX dosage, and NS dosage on the stone formation rate, viscosity, setting time, mechanical properties, and permeability of cement grout materials were explored based on single-factor experiments, with cementitious capillary crystalline waterproofing materials—XYPEX (CCCW-XYPEX), nano-SiO₂ (NS), and cement as the main ingredients, and polycarboxylate superplasticizer (PCS) as an additive. XRD, SEM, and MIP microtechniques were employed to analyze the hydration phases, microscopic morphology, and pore structure of the composite grouting material. The results show that after adding XYPEX and NS, the stone rate of cement slurry reaches 100%, and the setting time is shortened. The maximum decrease rates of slurry viscosity under the conditions of W/C and PCS content are 50.96% and 35.64%, respectively. When XYPEX : NS < 3 : 1, NS dominates and the slurry viscosity increases. When W/C increases from 0.4 to 0.5, the compressive strength of the specimen decreases rapidly. When the content of XYPEX is less than or equal to 3wt%, the early strength decreases and the later strength increases. When the NS content is less than or equal to 1wt%, NS mainly improves the early strength. When the PCS content increases from 0.2wt% to 0.3wt%, the strength of the specimen is improved. When W/C is 0.4 and PCS content is 0.3wt%, the relative permeability coefficient of the consolidated body is the smallest. When the content of XYPEX is more than 3wt%, it is not conducive to the early structural development of the consolidation body. When the NS content exceeds 1wt%, excessive NS will lead to a larger interface size of the gel material and an increase in water permeability. The microscopic analysis shows that the porosity of cement paste is reduced by mixing 3wt% XYPEX and 1wt% NS, single mixing 1wt% NS or 3wt% XYPEX, and the porosity of cement paste is reduced by 54.46% by mixing XYPEX and NS. XYPEX and NS improve the pore structure of the consolidated body through the catalytic-complexation-precipitation ability and nano-filling effect.