Early age reaction, rheological properties and pore solution chemistry of NaOH-activated slag mixtures

Abstract

In this study, the rheology and early reaction process of sodium hydroxide-activated ground granulated blast furnace slag (GGBFS) were investigated. Test results showed a strong relationship between the Vicat initial setting time and ultrasonic pulse wave for NaOH activated slag mixtures identifying the characteristic points or inflection points in the ultrasonic curves and reaching a specific value in the ultrasonic velocity. The early reaction process of the sodium hydroxide-activated slag pastes determined by ultrasonic pulse wave and calorimeter consisted of three stages: dissolution, acceleration/condensation and deceleration stages. The yield stress and apparent viscosity of the pastes increased by the addition of NaOH, and the pastes started to show shear-thickening behavior when NaOH concentration reached 8 M. It was also revealed that Si, Al and Ca ion concentrations in the pore solution increased with an increase in NaOH concentration, and the pore solution of the pastes was dominated by Na and OH−. No significant influence of NaOH concentrations upon 4 M on the compressive strength of the mortar samples was observed.