Electrically Induced Microstructural Changes in Portland Cement Pastes

Portland cement pastes 1 day to 1 month old were each subjected to a single cycle of 1250 V/m electric field (15 s forward, 15 s off, 15 s reverse) and analyzed for microstructural/transport changes by impedance spectroscopy. All samples experienced an irreversible increase in resistance, as much as 20–25%, which decreased with increasing age of the paste. Subsequent applications of field produced no additional changes. The resistance increases were shown to be attributable to decreases in pore network connectivity rather than to changes in overall degree of hydration, capillary porosity, or pore fluid conductivity. It is proposed that electro-osmotic swelling of product near “bottleneck” pores results in the decreased connectivity. Ramifications for electrocuring, electromigration, electrochemical chloride treatment, and permeability studies of cement based products and structures are also discussed.