Magnetic Nanoparticle Constructs for in situ Repair of Critical Cementitious Infrastructure

Abstract

Cement barriers in critical infrastructures, such as nuclear waste containment, can degrade and crack over time, enabling radionuclide release and further failure mechanisms. Repair in such hazardous scenarios is challenging, creating demand for remotely applicable solutions. This paper investigates silica-coated magnetic nanoparticles (NPs) as a novel gelling material for sealing microcracks in cement. The nanofiller is developed by coating magnetic nanoparticles with a silica shell using the water-in-oil emulsion method. The magnetic core enables targeted emplacement of the NPs within cracks, whereas the silica shell undergoes gelling through siloxane network formation upon destabilization. The developed silica-coated magnetic nanoparticle constructs exhibit high stability due to surface charge repulsion. Application of a 0.48 T magnetic field locally concentrate the NPs, overcoming electrostatic stabilization and inducing coalescence and subsequent gelation. This allows for the development of a magnetically drivable filler, that can be concentrated at the defect location and subsequently gelled.X-ray computed tomography (X-ray CT) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) demonstrated the effectiveness of this process in filling artificial crack geometries, providing insights into the 3D spatial and temporal evolution of the repair. Moreover, Scanning Electron Microscopy combined with Energy Dispersive X-ray Spectroscopy analysis provided evidence of additional calcium-silicate-hydrate formation resulting from the reaction of the nanofiller with cations present in the cement. These results show for the first time that magnetic concentration can overcome charge-based stabilization of silica-coated nanoparticles, enabling their use as highly effective material for sealing nano-and micro-cracks in physical barriers.