Studying the effect of alkali dosage on microstructure development of alkali-activated slag pastes by electrical impedance spectroscopy (EIS)

Abstract

In this study, electrical impedance spectroscopy (EIS) is applied to investigate the effect of alkali dosage on the microstructural evolution of the alkali-activated slag (AAS) system during the curing process. Pore solution chemistry and pore structure of the paste samples were also determined to get auxiliary interpretation of the EIS results. It is shown by equivalent circuit analysis that the resistance attributed to continuous (R1) and discontinuous pores (R2) increases with curing age due to pore structure development. The value of R1 is more affected by pore solution chemistry while the value of R2 is mainly affected by pore structure. With the increase of alkali dosage, the value of R1 decreases while R2 gradually increases. The exponent n of the constant phase element (CPE), which relates to the capillary pores (n1), decreases with the increase of alkali dosage while the exponent relating to gel pores (n2) is independent of the alkali dosage of AAS paste. The bulk conductivity of AAS paste obtained from the bulk resistance gradually increases with the alkali dosage, partially because of the enhanced conductivity of pore solution. The improvement of microstructure at early age is mainly attributed to the decreased porosity, which is more affected by the pore connectivity with the increase of curing age. These results confirm that EIS is an effective technique to determine the hydration properties and pore structure features of AAS paste.