Carbon nanotube char from hydrogen production as binder for stabilised soft sensitive clay

To reduce the high carbon footprint of cement in deep soil mixing, this study investigates using carbon nanotubes, a byproduct of green hydrogen production, as a partial cement replacement in soft clay. The effects of 20% carbon nanotubes substitution and accelerated carbonation on the shear strength and microstructure of stabilised clay were evaluated using consolidated drained triaxial tests, thermogravimetric analysis, and scanning electron microscopy. Results show that carbon nanotube addition significantly enhanced carbon dioxide uptake. This process led to a threefold increase in calcium carbonate content; however, it also reduced the primary binding agent, calcium-silicate-hydrate, by up to 60%. Geomechanically, individual treatments of carbon nanotubes or carbonation increased the effective cohesion by over 58% (from 95 kPa to ∼150–155 kPa). However, the combined treatment proved detrimental, reducing the effective cohesion to 60 kPa and the effective friction angle to 35·7°. The findings suggest that carbon-nanotubes-amended binders can reduce cement demand and enhance carbon dioxide sequestration in deep soil mixing, offering a viable pathway towards low-carbon ground improvement in infrastructure projects.