Electron-Conducting Carbon Concrete (ec³): A Multifunctional Structural Supercapacitor Material for Sustainable Smart Infrastructure

The following principal conclusions emerge from this investigation: 1.  A hybrid MWCNT-GNP-activated carbon system within a GGBS-modified Portland cement matrix can deliver simultaneous structural-grade compressive strength (up to 52.4 MPa, a 25.4% improvement over plain concrete control) and meaningful electrochemical energy storage capacity (specific capacitance up to 46.3 F/g; energy density up to 11.0 Wh/kg). 2.  The optimal formulation (ec³-3: 0.9 wt% MWCNT, 0.5 wt% GNP, 35 kg/m³ activated carbon) represents a Pareto-optimal balance, achieving the highest compressive strength (52.4 MPa) and highest cyclic durability (92.8% retention after 5,000 cycles) while delivering 83.6% of the maximum observed specific capacitance. 3.  Electrical percolation occurs at approximately 0.5 wt% combined CNT+GNP content, consistent with single-component CNT systems reported in the literature, indicating that the percolation threshold is governed by total high-aspect-ratio conductive filler volume fraction rather than specific composition — enabling cost-optimised formulation strategies. 4.  Three field-scale case studies across pavement, bridge, and facade applications confirm practical scalability, with field-measured performance within 3.9% of laboratory values, and functional payback periods of 2.1–4.0 years driven primarily by avoided sensor infrastructure and battery replacement costs. 5.  The embodied CO₂ penalty of ec³ (8–11% above conventional concrete) is modest relative to the dual structural and energy-storage functionality delivered, positioning ec³ as a technically and environmentally viable pathway toward self-powered, self-sensing smart infrastructure.

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