Alkali-activated cementitious materials for multifunctional structural capacitors: Multi-scale architectures, structure–property relationships and engineering applications

Smart infrastructure requires materials that simultaneously provide mechanical load-bearing capacity and active energy management functions. This article systematically analyzes alkali-activated cementitious materials as matrices for multifunctional structural capacitors, integrating strain sensing, Joule heating, electromagnetic shielding and absorption, and thermoelectric energy harvesting with in-situ storage. The review classifies existing concepts into four archetypes and elucidates the roles of three-dimensional conductive networks, hierarchical pores and interfaces, and ion-electron co-conduction across multiple scales. Design guidelines linking precursor chemistry, filler systems, and multi-scale architectures to specific functional targets are proposed, and cross-cutting structure-property relationships are synthesized. Key challenges including long-term multi-field durability, multifunctional interference, scale-up, and standardization are discussed. This work provides a framework for developing low-carbon, high-performance structural capacitors from industrial by-products.