Cement Energy & Environment

53 0.50 (vs. 0.90–0.95 for OPC) achieves ~0.35 tonnes CO 2 reduction per tonne cement. Integrated System: Combined approach (LC3 + biochar + mineral carbonation) achieves 0.5–0.7 tonnes CO 2 sequestration per tonne, approaching carbon-negative status versus baseline OPC (0.68 kg CO 2 /tonne). 2.2 Nanomaterial-Enhanced Carbon Storage Pathways 15-20% 20-30% 30% 15-25% 8-15% Nanomaterial Improvement Percentage Nano-Silica Nano-Titanium Dioxide Graphene Oxide Nano-Calcium Carbonate Carbon Nanotubes Fig.1: Impact of Nanomaterials on Carbon Storage and Concrete Properties Nano-Silica (Nano-SiO 2 ): Increases carbon capture efficiency by 15–20% through microstructural refinement. Nano-silica reacts with calcium hydroxide during cement hydration, producing dense C–S–H gel that reduces porosity and enhances CO 2 diffusion. At 0.25–3.8% by cement weight, nano-silica improves compressive strength by 11–37% while enabling enhanced carbonation kinetics. Service life extension of 20–30% maintains carbon storage benefits over extended periods. Nano-Titanium Dioxide (Nano-TiO 2 ): Facilitates photocatalyticcarbon sequestration through light- excited charge carrier mechanisms, increasing CO 2 sequestration capacity by 20–30%. At 0.5– 1.5% addition, nano-TiO 2 improves compressive strength by 4–8% and flexural strength by up to 8%. The photocatalytic activity provides self- cleaning properties and extends service life by 15– 20%. Under Indian tropical and semi-arid climates with high solar radiation, nano-TiO 2 offers region- specific advantages. Graphene Oxide (GO): Offers 30% CO 2 uptake improvement through high surface area (~2,500 m²/g) and multiple functional groups. GO- modified systems exhibit freeze–thaw resistance improvement (weight loss: 0.8% → 0.25% after 540 cycles), enhancedchloridepermeability resistance (40–60% reduction in diffusion coefficient), and superior high-temperature performance (residual strength at 1000°C: 35% → 70%). At 0.05% addition by cement weight, CO 2 sequestration improves without compromising workability. Nano-CalciumCarbonate (Nano-CaCO 3 ): Directly contributes to carbon storage while improving durability. Nano-CaCO 2 reduces water permeability by 30–50% and chloride diffusivity by 40–70%. Combined with nano-silica in fly ash concrete, nano-CaCO 2 increases carbon storage efficiency by 15–25% while enhancing corrosion resistance—critical for India’s coastal and urban environments. CarbonNanotubes (CNTs): Provide enhanced CO 2 diffusion pathways andmechanical bridging. CNT/ nano-SiO 2 core-shell structures maintain carbon sequestration benefits at elevated temperatures