Frequency- and Time- Domain Dependency of Electrical Properties of Cement-Based Materials During Early Hydration

The electrical properties of Portland cement, and cements containing supplementary cementitious materials (SCM), were obtained over the frequency range 1kHz-10MHz during the initial 24-hours after gauging with water. The response was measured in terms of conductivity and permittivity with both parameters exhibiting significant temporal changes during this period. It was also evident that whilst the conductivity increased only marginally with increasing frequency of applied electrical field, the permittivity decreased by several orders of magnitude over this frequency range. Moreover, certain features of the permittivity response – which are related to bulk polarization processes – only revealed themselves in the higher frequency range (100kHz-1MHz), and went undetected at lower frequencies. The detailed frequency- and time- domain measurements allowed identification of several stages in the early hydration of cement-based materials and the response can be interpreted in terms of hydration kinetics, physico-chemical processes and microstructural development. It is shown that the methodology can be equally applied to cement-pastes and concretes.