Insights into the effect of CNTs on cement hydration from the perspective of water evolution

Abstract

The addition of carbon nanotubes (CNTs) into cement can remarkably enhance the mechanical properties of concrete. To investigate the impact of CNTs addition on the early-stage hydration of cement paste, low-field nuclear magnetic resonance (NMR) was employed to monitor the water evolution and microstructure of cement paste. The relaxation signals obtained from low-field NMR can provide valuable information regarding the state and content of water molecules, thereby indirectly characterizing the microstructural change of cement. Based on the correlation of characteristic transverse relaxation T 2 and water confinement state, low-field NMR can be used to predict the setting time of cement in the early stage. The findings indicated that the addition of CNTs can expedite the initial hydration process of cement, leading to a denser microstructure and shorter setting time. The results of Vicat needle test validated the efficacy of low-field NMR in predicting the setting time of cement. The non-destructive and non-invasive nature of low-field NMR technology renders it particularly advantageous in assessing the impact of CNTs on the early-stage behavior of cement paste.