Investigation of hydration and setting process in nanosilica-cement blended pastes: In situ characterization using low field nuclear magnetic resonance

Abstract In order to characterize the effect of nano-SiO2 addition on early properties of Portland cement paste, low-field nuclear magnetic resonance (NMR) was used to monitor the hydration process and microstructure evolution. The relaxation signals of low-field NMR can provide the information about the water molecules status and corresponding content, thus indirectly revealing the microstructure evolution of cement paste. Based on the relaxation signals, new applications of low-field NMR in predicting the strength and setting time of cement were developed. The results indicate that the increasing nano-SiO2 addition as well as decreasing water-to-cement ratio can accelerate the early hydration process of cement and densify its microstructure, thus shortening the setting time and enhancing the early compressive strength. The effectiveness of low-field NMR in predicting the strength and setting time of cement was confirmed by the results of compression test and Vicat needle test, respectively. Due to the non-destructive and non-invasive characteristics of low-field nuclear magnetic resonance technology, this method shows special advantages in characterizing the influence of nano-silica on the early performance of cement paste.