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

• The 29Si longitudinal relaxation time (T1) for the anhydrous C3S was studied.
• The T1 for the remnant C3S in hydrated pastes and C–S–H was also studied.
• The anhydrous C3S has considerably long T1.
• The remnant C3S in hydrated pastes has considerably shorter 29Si T1 than the anhydrous C3S.
• The T1 of the signals of the remnant C3S and C–S–H gel in hydrated pastes are considerably similar.

29Si magic angle spinning nuclear magnetic resonance (29Si MAS NMR) has been commonly used to monitor the hydration degree of tricalcium silicate (C3S) 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 (T1) for the different types of Si in the structure of anhydrous triclinic C3S, the remnant C3S 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 29Si signals of C3S remaining after hydration are considerably shorter than the anhydrous C3S phase of the starting material; an effect that was interpreted as an extra contribution of 29Si–1H dipolar relaxation provided by the surrounding water molecules. Interestingly, the shorter T1 of the remaining non-hydrated C3S which is comparable to the C–S–H gel permits a much faster acquisition of quantitative 29Si MAS spectra.