BASIC RESEARCH ON THE NON-INVASIVE MEASUREMENT OF THE WATER CONTENT AND CHLORIDE CONCENTRATION IN CONCRETE BY MEASURING THE IMPEDANCE

For non-destructive and non-invasive inspection of water content and chloride concentration of concrete, a new electric method, by measuring the impedance between two rectangular metallic electrodes setting on the surface of the sample using the impedance meter with an AC voltage at frequencies of 10 Hz to 100 kHz was proposed. This paper describes the basic research of this easy, cheap, onsite, and non-invasive inspection system. First, the effects of water content and chloride concentration on the measured impedance dependence of frequency of small concrete samples were investigated. Secondly, the phase shift dependence of frequency was measured to estimate water content and chloride concentration individually by the peak of the phase shift and its frequency. Finally, the equivalent circuit of concrete that reproduces the curve of measured phase shift dependence of frequency by fitting the curves obtained from the equivalent circuit and measurement was proposed. It was shown that there is a possibility to estimate the water content and chloride concentration of concrete.