Large scale production of carbon nanotubes in portland cement

A process for forming carbon nanotubes/cement clinker composite by adding from 0.05% to 1% of carbon nanotubes onto cement clinker, wherein the cement clinker is used as a catalyst support for growing the carbon nanotubes by anchoring transition metals, the process comprising:

• (a) enriching and activating basic cement clinker in solid phase and/or liquid phase with transition metal oxides and/or salts both containing transition metal cations by
• (I) dissolving transition metal compounds as solute in a solvent to provide a solution mixture,
• (II) adding the solution mixture containing dopant metals to the cement clinker until a homogeneous mixture is reached, including a posterior drying stage for evaporation of the solvent, and
• (III) calcination of the homogeneous mixture at temperature from 200° C. to 800° C.;
• and
• (b) introducing enriched cement clinker into a kiln of controlled and reducing atmosphere with injection of light hydrocarbons and addition of inert gas as carrier at high temperatures effective to promote pyrolysis and to grow carbon nanotubes on the cement clinker by chemical vapor-phase deposition.