Novel Nano-Chemical Additives for Reducing Carbon Emissions During Cement Mixing and Hydration

Abstract

The cement industry is one of the largest industrial sources of anthropogenic carbondioxide emissions. The principal sources of these emissions are limestone calcination, fuel combustion during clinker production, electricity consumption during grinding, and the large quantity of Portland cement required to achieve the required mechanical and durability performance.This research investigates advanced nano-chemical additives capable of reducing thecement and clinker content required in cement-based materials while maintaining or improving mechanical strength, durability, hydration efficiency, and service life. The investigated additives include nano-silica, graphene oxide, nano-calcium carbonate, nano-alumina,nano-clay, carbon nanotubes, and nano-biochar.The behavior of these additives is interpreted using cement hydration thermodynamics, nucleation and growth theory, diffusion-controlled kinetics, colloidal stability, capillaryporosity theory, fracture mechanics, and life-cycle carbon accounting. Nano-silica operatesprincipally through heterogeneous nucleation, pozzolanic reaction, calcium hydroxide consumption, and pore refinement. Graphene oxide provides additional nucleation surfaces,calcium-ion adsorption, crack bridging, and interfacial reinforcement. Nano-calcium carbonate promotes early hydration and carboaluminate formation, while nano-alumina and nano-clay modify the formation of alumina-bearing and aluminosilicate hydration products.The environmental benefit of nanotechnology does not result simply from adding nanoparticles to cement. It results when the nanoparticles reduce clinker demand, increase the degree of hydration, refine the pore system, reduce structural dimensions, extend service life,or enable a greater replacement of Portland cement by supplementary cementitious materials. Therefore, the net carbon benefit must be evaluated by comparing avoided cement emissions with the embodied carbon of the nano-additive and its production process.