Effect of CNT-FA hybrid on the mechanical, permeability and microstructure properties of gangue cemented rockfill

Solid waste resource reuse, such as fabricating cemented rockfill material, plays a central role in underground reinforcement projects and construction waste recycling. However, the cement applied in the cemented rockfill material still brings massive CO₂ emissions and energy consumption. Hence, we take the 0.009 wt% carbon nanotubes (CNTs) combining fly ash(FA) to replace 20% cement to explore a more sustainable improvement for cemented rockfill material. The results demonstrated that CNTs modified specimens exhibited a 17.6% reinforcement in elastic modulus, while the compressive strength remains almost unchanged. The modified specimen also shows fewer and sparser acoustic emission activities, indicating lower destruction intensity. Furthermore, with the help of CNTs filling the pores, water sorptivity and gas permeability tests showed that the impermeability improved by 8.4%-19.7%. By calculating the fractal dimension of the fracture surface SEM images, the CNTs reinforced specimens show better integrity and less structural damage. Metal intrusion measurements indicated that CNTs minify the ITZ width, split micropores in ITZ to reduce porosity under all equalized diameters significantly, especially at 65–70 μm, and form a network skeleton in the pores at the edge of the ITZ to prevent pores from connecting with microscopic defects in the cement matrix. The findings of this work can enhance the understanding of CNTs in composites fabrication and guide the application of CNTs in construction, transportation and mineral engineering in the future.