Dielectric properties of the pore solution in cement-based materials

Composition changes in the pore solution affect significantly the dielectric response of porous materials? The presence of ions is recognized to affect the dielectric response of electrolytes in a complex way that depends on the ion-water and ion-ion interactions and respective concentrations. Pore solutions in cement-based materials are complex and age-dependent exhibiting different ion-pair states, which make them an interesting candidate for the study of the complex pore solution found in geomaterials in general. In cement-based materials, the measurement of dielectric properties is used for non-destructive monitoring and assessment of concrete structures conditions and to unravel details of the hierarchical pore structure of the material, notably at early-age when the microstructure of the material changes significantly. Here, we study the dielectric properties of bulk aqueous solutions representative of the pore solution found in cement-based materials using molecular dynamics simulations. Broadband dielectric spectra and frequency-dependent conductivities are provided. We show that the changes in the ionic composition of the pore solution due to the aging of the material translate in significant changes in the dielectric response: the static dielectric constant varies from 55.2 to 73.9. A mean-field upscaling strategy is deployed to compute the dielectric response at the cement-paste scale. Our results can be used in the interpretation of high frequency electromagnetic methods, such as ground-penetrating radar, enhancing the quality of interpretation and improving the confidence in the corresponding results