Carbon nanotubes assisted fly ash for cement reduction on the premise of ensuring the stability of the grouting materials

Abstract

Cement-based grouting is the most used method to strengthen the fractured rock mass and reinforce the mechanical properties and impermeability of the surrounding rock. The balance among the strength, durability, workability and cost of the grout has always been the key to grouting engineering. In this study, we use carbon nanotubes (CNTs) as the nano-additive to assist fly ash in preparing high-performance cement-based grouting materials. The results show that CNTs can generate nucleation effects and pore-filling effects in cementitious composites to promote the hydration reaction of the grouting materials and optimize the pore structure of the hardened slurry. Two reinforcing roles, bridging and pulled-out role of CNTs, act in the hardened cement matrix, where the former can improve the mechanical properties of grouting materials through micro-friction toughening, and the latter can form a net-like distribution in cement matrix together to enhance the impermeability. More importantly, we found that 0.08 wt% CNTs combined with 20 wt% fly ash can be a good substitute for cement with a moderate proportion of grouting materials. Compared with plain cement slurry, the mechanical properties are basically unchanged, while the workability can be increased by about 5%, and the impermeability can be reinforced by 6%. The discovery of this research provides an excellent chance for utilizing the superior properties of CNTs to fabricate high-performance, cost-effective and environment-friendly grouting materials.