Improved non-contact variable-frequency AC impedance instrument for cement hydration and pore structure based on SVM calibration method.

• The instrument is used to study on pore structure of cement-based materials. • Standard resistance method is used to calibrate the modulus and phase of impedance. • SVM model is used to predict calibration value of modulus and phase of impedance. • SVM model has the best comprehensive performance among FT,ANN. The non-contact alternating current (AC) impedance method is widely used in the study of electrochemical properties of cement-based materials,the instrument of this paper provide a new way for the study of pore structure of cement-based materials. Due to the loss of magnetic materials and the parasitic capacitance of measuring circuit, the ratio difference and phase difference of current sensor inevitably exit. Traditionally the standard resistor calibration method is used to determine the ratio error and phase error under different frequencies based on polynomial fitting (FT). In this paper, a machine-learning support vector machine (SVM) model is used to predict the calibration data with a small test sample. For the accuracy assessment, SVM model has the best comprehensive performance among FT, artificial neural network (ANN). The actual impedance test of typical cement-based materials under different frequencies is given and the results verify the excellent performance of SVM. [ABSTRACT FROM AUTHOR]