Electric-field effect on ITZ refinement and HD C-(A)-S-H gel formation via electro-thermal field decoupling in cement composites

Cement hydration is traditionally viewed as a passive thermochemical process. Here, we demonstrate that it can be actively regulated by external fields. A reinforced-concrete platform was designed to decouple electric and thermal fields, enabling controlled field modulation within a realistic macrostructure. Using statistical nanoindentation, BSE-EDS mapping, and multivariate clustering, we reveal distinct pathways of field-driven hydration. Temperature primarily enhances the densification and stiffness of high-density C-(A)-S-H, whereas the electric field induces charge-guided Si-Al redistribution and gel homogenization across densities. The interfacial transition zone determined by mechanical properties narrowed, with modulus and hardness increasing by 13.6 % and 27.6 %, respectively. These insights establish a field-programmable paradigm for electro-thermal curing, where targeted electric stimuli reconfigure nanoscale hydration networks beyond conventional thermal effects. This work bridges macro-scale construction and microstructure design, offering a pathway toward intelligent, low-temperature cementitious materials.