EXPERIMENTAL STUDY ON PROPERTIES AND MICROSTRUCTURE OF NANO MODIFIED ULTRAFINE CEMENT-BASED GROUTING MATERIAL

The traditional cement-based grouting materials commonly used for repairing cracks in highway tunnels have large particle sizes and are easy to block pipes. As such, ultrafine cement-based grouting materials were modified by adding nano-silica (NS), nano-alumina (NA), and carbon nanotubes (CNTs) to improve their grouting, stability, and strength. The results showed that after adding different nano-materials, the fluidity and setting time of the grouting slurry decreased to different degrees, and the maximum values decreased by 41.38% and 42.9%, respectively. Among them, CNTs had the most significant effect, followed by NS. At the same time, the water bleeding rate of the grouting slurry decreased. When 2% NS and 0.5% CNTs were added, water bleeding would not appear. The compressive strength of nano modified grouting materials at all stages would increase first and then decrease with the increase of dosage. The dosages of NS, NA, and CNTs were 1.0%, 1.0%, and 0.1%, respectively, and the compressive strength increased by 24.6%, 4.2%, and 9.2% in 28 days, respectively. X-ray diffraction and scanning electron microscopy tests showed that the surface effect of NS and CNTs can improve the hydration reaction efficiency and hydration products; bridging and nucleation can reduce the crack spacing and structural pores between different particles, and improve the connection between hydration products. The amorphous materials produced by NA can fill the pore structure, while the cementation performance of amorphous materials was poor and had limited contribution to the strength.