Correlating the Chloride Diffusion Coefficient and Pore Structure of Cement-Based Materials Using Modified Noncontact Electrical Resistivity Measurement

The electrical resistivity of hardened cement-based materials was measured in this work by a modified noncontact electrical resistivity measurement (MN-CM). The resistivity was further processed to compute the chloride diffusion coefficient ($D_{\rho }$) using the Nernst-Einstein equation. Also, the rapid chloride migration test (RCM) was carried out to obtain the chloride migration coefficient ($D_{\mathrm{RCM}}$), and the relationship between $D_{\rho }$ and $D_{\mathrm{RCM}}$ has been established. The obtained $D_{\rho }$ was further correlated to the pore structure parameters characterized by low-field nuclear magnetic resonance (NMR) spectroscopy. The results show that the $D_{\mathrm{RCM}}$ is more sensitive to the change of pore connectivity, while $D_{\rho }$ is more sensitive to the change of porosity. The $D_{\rho }$ is smaller than $D_{\mathrm{RCM}}$ since it strictly follows the Nernst-Einstein equation while RCM neglects the other driving forces such as capillary sorption and concentration gradient. It is concluded that the proposed MN-CM can obtain the chloride diffusion coefficient of saturated cement-based materials in a quick, stable, and reliable manner.