Revealing the role of Fe particle size in soft magnetic geopolymer for enhancing energy conversion in airport pavement induction heating

In this study, a soft magnetic geopolymer (SMG) co-modified with nanomagnetic fluid and spherical micron-sized Fe powders was developed for enhancing the energy conversion in airport pavement induction heating. The effects of Fe particle size on the microstructure, electromagnetic behavior, and mechanical performance of SMG were systematically investigated, with a focus on the size-dependent coupling mechanisms. Results show that Fe powder with a particle size no less than 150 μm provides pore-filling and skeletal reinforcement, leading to improved compressive strength and stable magnetic permeability. In contrast, finer particles significantly increase the specific surface area, which intensifies internal demagnetizing fields and magnetic flux pinning, thereby reducing saturation magnetization and coercivity. Simultaneously, excessive water demand caused by fine particles suppresses geopolymer gel formation, resulting in increased porosity and decreased mechanical strength. COMSOL simulations confirm the development of localized demagnetizing fields around smaller Fe particles. Indoor induction heating tests further reveal that the incorporation of SMG improved the energy conversion efficiency during induction heating by 19.4 % when the Fe powder particle size was not less than 150 μm, demonstrating its potential for energy-responsive, structure-integrated infrastructure.