Study on the workability and early mechanical properties of carbon nanotube-coated fly ash modified cement-based grouting materials

Abstract

Carbon nanotube (CNTs) reinforced cementitious composites have obvious advantages over traditional building materials in strength and impermeable durability. However, the material in question has not been widely employed in grouting engineering due to the limitations posed by dispersion issues. This study introduces a novel method of using amino functional groups to coat carbon nanotubes on the surface of fly ash to improve dispersion. The objective is to produce high-quality industrial-grade slurry and facilitate the transition of carbon nanotubes from small-scale research to large-scale engineering applications. The results show that mixing 14.3 wt% fly ash and 0.023 wt% CNTs in cementitious composites can replace an equivalent proportion of cement. Compared to traditional cement-based grouting material, the modified composites exhibit a 21.6 % increase in fluidity, a 7.9 % increase in the 7-day consolidation strength, and an 11.9 % reduction in the porosity of the slurry consolidation. The CNTs with large specific surface area on the fly ash surface provide sites for cement hydration reaction, accelerate cement hydration, and form dense hydration products. Additionally, the interaction between hydration products and CNTs within the microcracks of the cement matrix forms a 'bridging role' that enhances mechanical properties. The effectiveness of incorporating CNTs in reducing micro-damage during the loading process of slurry consolidation, enhancing integrity, and improving the grouting material's resistance to loading was further proved by acoustic emission, scanning electron microscopy, and fractal analysis of the fracture surface.