Chloride diffusivity in hardened cement paste from microscale analyses and accounting for binding effects

Area of Science:

• Civil and Materials Science
• Chemical Engineering
• Computational Mechanics

Background:

• Hardened cement paste (HCP) exhibits complex microstructural heterogeneity.
• Understanding chloride ion diffusion is critical for predicting concrete durability.
• Chloride binding significantly influences the effective diffusion process.

Purpose of the Study:

• To investigate chloride ion diffusion in HCP under steady-state conditions.
• To account for material heterogeneity and ion-binding interactions.
• To derive a homogenized diffusivity for HCP.

Main Methods:

• Utilizing X-ray imaging and CEMHYD3D simulations for microstructure analysis.
• Incorporating physical and chemical interactions of chloride ions with HCP phases.
• Applying a least squares homogenization technique to derive diffusivity.

Main Results:

• Numerical simulations successfully captured chloride diffusion dynamics.
• Homogenized diffusivity values were derived based on microstructural features.
• Model predictions showed good agreement with existing experimental data.

Conclusions:

• The developed model accurately represents chloride diffusion in heterogeneous HCP.
• Accounting for ion binding and microstructure is essential for reliable predictions.
• This approach enhances the assessment of concrete service life.