Turning waste to function: scalable fly ash-based building materials with structural, energy storage, and electrothermal capabilities

The demand for sustainable construction materials with multifunctional capabilities, including integrated energy storage, is growing as modern infrastructure evolves beyond traditional load-bearing roles. Addressing this need, we introduce a scalable and cost-effective material (GeoAsh) derived from fly ash, an industrial solid waste. The abundant silicates and aluminates in fly ash exhibit high reactivity under alkaline activation, providing promising mechanical support comparable to that of widely used Portland cement. Uniquely, the presence of approximately 9 wt.% Fe 2 O 3 content in fly ash serves as an intrinsic oxidizing agent, facilitating the polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT). This functionalization endows this construction material with superior electrothermal and electrochemical performance, while maintaining considerable mechanical strength (∼38 MPa). The resulting PEDOT-coated GeoAsh composites exhibit a rapid joule-heating response, maintaining functionality under extreme temperatures as low as -10 °C, thereby indicating significant potential for advanced de-icing applications. Additionally, the PEDOT-coated GeoAsh composites can work as electrodes in a structural supercapacitor (SSC), reaching a remarkable areal capacitance of 997 mF cm -2 under two-electrode configuration testing. It provides an excellent areal capacitance of up to ⁓926 mF cm -2 using a gel electrolyte and an exceptional energy density of ∼129 µWh cm - ² at a power density of 0.5 mW cm - ², highlighting its potential for energy storage applications in the construction sector.