Effect of Drying Methods on Microstructural Changes in Hardened Cement Paste: an A. C. Impedance Spectroscopy Evaluation

Abstract

The effect of three pre-drying treatments on time dependent deformation due to drying of cement paste conditioned at (96 ± 2) % relative humidity and temperature of 22 ± 2 °C was investigated using a.c. impedance techniques. The treatments comprised methanol and isopropanol exchange (followed by vacuum heating at 37°C) and vacuum drying at 37°C alone. Re-saturation with synthetic pore fluid was performed prior to the drying experiment. Real-time changes in microstructure were followed using impedance spectroscopy. Cement paste specimens were in the form of “T-shaped” columns with a minimum thickness value (for the web and flanges) of less than 1.2 mm. The impedance spectra for the untreated (control) specimens and the specimens dried at 37°C indicated the presence of an intermediate arc. This is discussed in terms of interfacial phenomena associated with collapse of C-S-H structure on drying.