Effects of microstructure and pore water on electrical conductivity of cement slurry during early hydration

Abstract

In this study, inductance-type electrical conductivity measurement (IECM) was performed to study the electrical conductivity of different formulations of cement slurry. Low-field nuclear magnetic resonance, in situ X-ray micro-tomography, and environmental scanning electron microscopy were used to investigate the effects of the microstructure, pore characteristics, and pore water of cement slurry on its electrical conductivity. Experimental results showed that the pore characteristics and ion concentration governed the initial electrical conductivity of fresh cement slurries. The sedimentation stability of fresh cement slurries increased the number of interconnected pores, and the initial electrical conductivity increased from 16.8 mS/cm to 19.4 mS/cm. When the CaCl2 accelerator content was 2 wt%, the initial electrical conductivity of the fresh cement slurry increased to 26.9 mS/cm, while the electrical conductivity rapidly decreased with the formation of hydration products. With increasing hydration time, large amounts of hydration products were formed in the pores, which changed the microstructure and pores of the cement slurry from connected large volume pores to many small volume pores and subsequently changed the distribution of pore water. The experimental results revealed that the connected porosity of the cement slurry was proportional to the electrical conductivity. An exponential relationship was found between the electrical conductivity and the evaporable water content, whereas a linear relationship was found between the electrical conductivity and the free water content.