Synergistic Utilization of Porous Coral Sand and Fly Ash for Multifunctional Engineered Cementitious Composites with Polyethylene Fibers: Intensified Electromagnetic Wave Absorption and Mechanism

The large-scale consumption of industrial solid waste for fly ash is imperative for clean material production. Among these, abundant coral sand is a potential alternative to river silica sand in construction materials. This study proposes an environmentally friendly synergistic utilization of coral sand as a natural porous aggregate that can be incorporated with fly ash and polyethylene (PE) fibers to prepare multifunctional engineered cementitious composites (ECCs) with good electromagnetic (EM) wave absorption and mechanical properties. The effects of porous coral sand, PE fibers, and fly ash on the EM parameters, hydration products, pore distribution, microstructure, and reflection loss of the ECCs were systematically investigated. The mechanical properties and environmental impact were also examined. The results showed that the synergistic integration of porous coral sand, PE fibers, and fly ash optimized the pore distribution, attenuation paths, impedance matching, multiscattering effect, nanoscale effect, and interfacial polarization of the ECCs, which were conducive to the intensification of EM wave absorption. In particular, the appropriate use of natural coral sand as porous aggregates increased the EM wave absorption, while retaining the mechanical strength and excellent tensile properties of the ECCs. Environmental impact assessment showed that the alkalis of the prepared multifunctional ECCs were solidified in the C–S–H gels, which cannot be easily ionized, thereby inhibiting environmental pollution.