The temporal change in electrical properties is used to study the hydration kinetics of chemically activated fly-ash systems at room temperature. Four low-lime ashes and one high-lime ash were used in the experimental programme and the electrical response was measured in terms of the in-phase (i.e. conductance) and quadrature (i.e. capacitance) components of the sample admittance. The low-lime ash and high-lime ash exhibited markedly different electrical response. The work highlights the applicability of the testing methodology as a non-invasive, non-destructive technique in the assessment of the efficacy of a particular activator or combination of activators. © 2005 Springer Science + Business Media, Inc.