Application of A.C. impedance techniques in studies of porous cementitious materials (III): ACIS behavior of very low porosity cementitious systems

The microstructure of very low porosity cement and cement-silica fume paste systems was investigated by A.C. impedance spectroscopy (ACIS). The theoretical relationship between ACIS parameters and the structure of porous materials previously proposed by authors has been confirmed for these systems. Results indicate that a delayed appearance of the high frequency semicircle, present in spectra of normal cement pastes at high water/cement ratios, does not occur in the present cases due to their lower initial porosity. The high frequency arc diameter, R₂, increases significantly with hydration time and compacting pressure; this is compatible with results from other measurements, e.g. mercury intrusion porosimetry, helium pycnometry, etc. The densification effect of silica fume in very low porosity systems has also been demonstrated. It was found that there is an optimum addition of silica fume at which R₂ has a maximum value. It is apparent that ACIS techniques are applicable to studies of the microstructure of very low porosity cementitious systems.