Effects of electrochemical chloride extraction on hydrated products of various cement paste systems

Abstract

The adverse effects of the long term application of electrochemical chloride extraction on binding capacity of hydrated cement products are innegligible. In this study, the influences of electrochemical chloride extraction in the microstructural properties of hydrated cement products of cement pastes were investigated in paste specimens by using a modified migration cell that was conducted with the applied current density of 4.5 A/m2 and synthesized pore solutions as electrolytes for 8 weeks. Three types of cement pastes were used with the water-to-binder ratio of 0.4 including ordinary Portland cement (OPC), fly ash cement (FC) and ground granulated blast furnace slag cement (SC) pastes. Chloride source was supplied by adding 1.5% sodium chloride. After extraction, the acid-soluble and water-soluble chloride contents significantly reduced. Portlandite content increased proportionally with the time of extraction in OPC and FC pastes although the contribution of calcium ions in transferring the current is negligible. Some unsteady gel phases was obtained after a short time the extraction was stopped. Furthermore, the alteration and decomposition of C-S-H were inevitable with different rates depending on the type of cement.