Preliminary electrochemical cementation of high volume fly ash mortars

Abstract

This paper summarizes a research about the electrochemical activation of the cementitious properties of fly ash. Taking into account that in recent years there have been various environmental issues associated with the production of Portland cement (PC), the use of Fly Ash (FA) has been promoted in the production of concrete. Traditionally, the use of fly ash has been possible through its blending with Portland cement and as a geopolymeric cementitious material. In this research, a third technique for fly ash activation, known as electro-mutagenesis, was investigated. This treatment consisted in the late hydration of fly ash after the migration of ions from an external alkaline solution, by applying an electric field across the hardened mortar. Solutions of sodium hydroxide and sodium silicate with different molar concentrations were used as a source of alkaline ions. The electrical treatment was applied in many mortar samples using high volume proportions of fly ash, a constant water to binder ratio, and a fixed aggregate content. After treatment, the compressive strength, the ultrasonic pulse velocity, and the microstructure of the mortar matrices were investigated. Results showed that the alkaline ions migrated into the hardened mortar through the permeable capillary pores, reacted with the un-hydrated fly ash and mutated in new hydration phases, producing an improvement in the physical properties of mortar.