Impact of freezing conditions on the characteristics of ultra-low water binder ratio cementitious composites (ULCC): Towards to hydration mechanism and molecular migration model

This study aims to clarify the hydration kinetics and microstructure development of ultra-low water binder ratio cementitious composites (ULCC) at cryogenic temperatures based on experimental and numerical approaches. More exactly, the micro and macro properties of ULCC are firstly investigated by experiments and then the hydration mechanism is analyzed by NMR and molecular dynamics methodology. The results reveal that the hydration of ULCC can still be triggered at −20°C, while the hydration process is significantly delayed and the theoretical maximum hydration degree drops to 59.72 % of room temperature. When the temperature is further reduced to about −80°C, the hydration of ULCC is prevented, while the crystallization of the original product and the C-S-H chain length is decreased. However, in this case, the hydrogen bond stability of water between layers of C-S-H gels is improved, which can be confirmed by molecular simulation. Finally, a hydration kinetic model is constructed to quantitatively predict the development of water migration process and hydration degree in ULCC at freezing temperature.