Pore reduced cements (PRC) are used as a high resistance matrix for ac impedance studies on cement systems with impedance data being collected over a range of temperatures (-60 to ca. 20 degrees C) and electrode contact pressures (up to 72 MPa). The results show the presence of two arcs in the complex impedance plots, Z*, at all measured temperatures. The low frequency (LF) arc is attributed to an ineffective electrical contact at the sample/electrode interface and although the high frequency (HF) arc is associated with the cement, its characteristics are also influenced by the contact resistance. Arrhenius plots show the activation energy for conductivity associated with the LF and HF elements to be the same indicating similar conduction mechanisms. Low and high frequency arcs are resolved only by the different geometric factors (conductive volumes) associated with the ineffective contact and the bulk cement specimen. (C) 2000 Kluwer Academic Publishers.