Differential analysis of AC impedance spectroscopy of cement-based materials considering CPE behavior

A differential impedance analysis method considering constant phase element (CPE) was proposed for cement-based materials. Results indicated that the method is very accurate for the identification circuit of single capacitive loop. For series circuit of double capacitive loops, the method can accurately identify all impedance parameters when ratio (q) of the two time constants is large. For series and parallel circuits of double capacitive loops, even when q is close to 1, number of the capacitive loop can be identified accurately. The method can selectively identify the variation, frequency range and frequency dependence of the impedance parameters of cement-based materials; it can also explain why when two capacitive loops exist in a Nyquist plot of cement-based materials, only one can be observed by the naked eye. The method is beneficial for establishing a reasonable equivalent circuit of impedance spectroscopy with a CPE behavior, especially when q is very small.