Impact of synthetic C-S-H seeds on early hydration and pore structure evolution of cement pastes: A study by 1H low-field NMR and path analysis

C-S-H seeds are highly-efficient in promoting hydration but not compromising the long-term performances of cement. Unfortunately, mechanisms of the C-S-H seeds properties affecting the early-age performances of cement are not very well understood. In this study, the influence of hydrothermal synthetic conditions on the C-S-H seeds properties is firstly investigated, followed by revealing the correlations of C-S-H seeds properties, hydration kinetics, and pastes performances by using in situ 1H LF-NMR and path analysis. It is found that low reactant concentrations and calcium-to-silicon ratios facilitate the production of C-S-H seeds with small size and high purity. Using C-S-H seeds with high effective surface area, i.e. nano-sized and high purity, the acceleration period of cement starts within 2 h and ends after 6 h, which in turn results in a refined pore structure and an enhanced strength, particularly at 12 h. An increased CH content leads to a decreased C-S-H growth rate.