Analysis of impedance data of silane-treated concrete obtained by four-probe method

Electrochemical impedance spectroscopy (EIS) using the four-probe method was investigated as a non-destructive testing technique for quantitatively evaluating the protective effect of silane-treated concrete. Silane-treated concrete exhibits distinct electrical characteristics between the surface silane-modified layer and the internal unmodified layer, and the impact of these characteristics on four-probe measurements had previously been unclear. To address this, four-probe EIS measurements were conducted on silane-treated concrete, followed by finite-element (FE) analysis to simulate the results and parametric studies to clarify the effects of silane penetration depth and the distribution of electrical properties. The actual silane-treated specimens exhibited an oval capacitive loop, attributed to the non-uniform thickness of the silane-treated layer. Furthermore, it was found that when the electrode spacing in four-probe EIS was reduced beyond a certain threshold, the measured electrical resistance significantly increased compared with larger electrode spacing. FE analysis suggested that this was due to the smaller electrode spacing causing the current to concentrate in the surface silane-modified layer, which has a higher resistivity.