Title:
Mitigating Chloride Ion Ingress in Cement Composite using Nanosilica (Prepublished)
Author(s):
Fulin Qu, Hanbing Zhao, Qiao Wang, Kejin Wang, Wengui Li
Publication:
Materials Journal
Volume:
Issue:
Appears on pages(s):
Keywords:
chloride ingress; durability; nanosilica; pozzolanic activity; quantified hypermaps; sulfate-chloride dynamics
DOI:
10.14359/51749257
Date:
10/8/2025
Abstract:
Building resilient infrastructure in chloride-rich environments presents significant challenges. This study examines the impact of nanosilica (NS) and ground granulated blast furnace slag (GGBFS) on chloride ingress in cement composites exposed to seawater, NaCl solution, and a combined NaCl-Na₂SO₄ solution. Analysis using microcharacterisation, BSE-EDS hypermaps, and thermodynamic modelling reveals that GGBFS enhances chloride binding by forming Friedel's salt (FSS) across all environments, effectively immobilizing chloride ions. NS further refines the cement matrix by densifying the calcium silicate hydrate (C-S-H) structure and generating additional C-S-H gels, improving physical chloride binding. This combined effect reduces porosity and strengthens resistance to chloride diffusion. Sulfate ions significantly influence hydration products and chloride binding, with excessive sulfate reducing FSS formation, thereby weakening chloride resistance. Sulfate may also convert FSS into monosulphate (AFm) and ettringite (AFt), altering chloride immobilization. Cement composites containing both GGBFS and NS demonstrated superior resistance to chloride and sulfate exposure, as confirmed by thermodynamic modelling. These findings provide insights into sulfate-chloride interactions and offer guidance for developing durable cementitious materials in aggressive environments.