## 3 Results and Discussion  
### The Evolution of NMR Transverse Magnetization During Hydration  
Considering it is linearly proportional to proton number and thus water content, the first peak amplitude of the transverse relaxation, which is approximately regarded as fitted magnetization \(M_{0}\) of the samples under the CPMG pulse sequence was collected. For convenience, the measured signal quantity at different times is divided by the initial water content in the sample to obtain the change of the transverse magnetization of the evaporable water during hydration, as shown in Figure 1. The samples with different water-to-cement ratios have similar evolution trends. The first-order derivative curves of the magnetization under different water-to-cement ratios were obtained by fitting the signal data. It is shown that the characteristic changes of the curves agree well with the known five stages of cement hydration process in the early stages of setting: initial reaction (stage 1), induction period (stage 2), acceleration period (stage 3), deceleration period (stage 4), and slow hydration reaction (stage 5). This is because the rate of water consumption in the cement paste is consistent with the rate of chemical reaction, i.e., the rate of heat release. At the same time, the higher water-to-cement ratio in the sample results in the greater magnetization for the remaining evaporable water, indicating that the amount of water consumed by the hydration reaction is less compared to that with low \(w/c\) ratio.  
For the samples with \(w/c\) = 0.3, 0.4 and 0.5, the initial setting times conducted according to Vicat needle tests are 1.6 h, 2.2 h, and 2.5 h, respectively. The corresponding final setting times are 2.6 h, 2.9 h, and 3.7 h, respectively. Thermodynamically, the initial set is marked by a rapid temperature rise, which corresponds roughly to the beginning of the main chemical reactions. This temperature rise will reach a maximum rate after the final set. The first-order differential curves of the NMR signal intensity in Figure 1 show that the actual measured initial setting times of the cement pastes occur shortly after the start of the acceleration period; while the measured final setting times appear before the end of the acceleration period. During the acceleration period, the chemical reactions were controlled by nucleation to by chemical process. The Ca(OH)\({}_{2}\) began to crystalline after achieving supersaturating concentration. The tricalcium silicate C\({}_{3}\)S (C = CaO, S = SiO\({}_{2}\), according to the cement chemistry notation) that the main component of the cement linker, began to hydrolyze acceleratively and produced C-S-H (C = CaO, S = SiO\({}_{2}\), H = H\({}_{2}\)O, according to the cement chemistry notation). As a result of these reactions, the pastes hardened and formed strength. The water in the pastes became relatively immovable, where more and more water was constrained in the micropores of the calcium silicate hydrates gels. A lower water-to-cement ratio results in a shorter initial and final setting times, and the valley and peak positions at the first derivative curve of the corresponding NMR signal intensity are shifted to the left.