Quantitative analysis of pure triclinic tricalcium silicate and C-S-H gels by 29Si NMR longitudinal relaxation time

Si magic angle spinning nuclear magnetic resonance (Si MAS NMR) has been commonly used to monitor the hydration degree of tricalcium silicate (CS) and the structure of the calcium silicate hydrate known as C-S-H gel generated during their hydration, which is responsible for the strength and durability of cement pastes. The present study is aimed to measure the longitudinal relaxation times (T) for the different types of Si in the structure of anhydrous triclinic CS, the remnant CS in pastes after a number of hydration days and the hydrated product (C-S-H gel). Results showed that the longitudinal relaxation times of the Si signals of CS remaining after hydration are considerably shorter than the anhydrous CS phase of the starting material; an effect that was interpreted as an extra contribution of Si-H dipolar relaxation provided by the surrounding water molecules. Interestingly, the shorter T of the remaining non-hydrated CS which is comparable to the C-S-H gel permits a much faster acquisition of quantitative Si MAS spectra.Peer Reviewe