Structuring lightweight concrete with core–shell Fe₃O₄@DFNS nanoparticles: a path to smart and durable cementitious materials

The integration of functional nanostructures into lightweight concrete (LC) offers a promising solution to address its inherent drawbacks, including high porosity, shrinkage, and limited durability under aggressive environmental conditions. This study evaluates the effect of Fe₃O₄@DFNS nanoparticles on the workability, ultrasonic pulse velocity (UPV), and durability of lightweight concrete. Experimental results show significant improvements in compressive strength, resistance to chloride ion penetration, and thermal conductivity, while maintaining the lightweight properties of the concrete. In this study, a novel core-shell nanocomposite comprising magnetic Fe₃O₄ nanoparticles encapsulated within dendritic fibrous nanosilica (Fe₃O₄@DFNS) was shown to enhance the performance of LC, particularly for marine applications. The Fe₃O₄@DFNS system was synthesized <i>via</i> a co-precipitation-sol-gel approach, combining magnetic dispersibility with high surface area and hierarchical porosity. Various dosages (0.05-0.35 wt%) were incorporated into LC mixes and evaluated through rheological, mechanical, thermal, and microstructural analyses. The optimal dosage (0.25 wt%) significantly improved workability and compressive strength by 30%, while reducing water absorption, porosity, and drying shrinkage. Durability assessments revealed a substantial enhancement in resistance to chloride ion ingress. Rapid chloride penetration test (RCPT), Fick's second law diffusion modeling, and chloride profiling confirmed over 45% reduction in penetration depth. Additional cyclic wetting-drying in artificial seawater showed 71% lower mass loss. Coupled FEM simulations validated improved stress distribution and delayed cracking, while X-ray CT revealed macro/micro void distribution and TEM confirmed the nanostructural features, together evidencing microstructural refinement. Furthermore, Fe₃O₄@DFNS reduced thermal conductivity by ∼20%, indicating potential for energy-efficient construction. The multifunctional behavior of this nanocomposite demonstrates its effectiveness as an intelligent additive for long-term durability and structural performance in coastal and marine-grade concrete.