# Experiment and Analytical Model for Pore Structure of Early-Age Composite Cement Pastes by LF-NMR
## 3 Results and Discussion  
### Pore Characteristics of Neat Cement Pastes  
Figure 3 illustrates the pore size distribution (PSD) of neat cement pastes with varying w/c ratios cured under standard conditions for 3, 7, 14, and 28 days. The PSD curves of WC30, WC35, and WC40 contain two peaks, and the height and area of the left peaks are bigger than the ones of the right peak. According to the research of [PERSON] et al. [30], the larger peak indicates the gel pores, whereas the smaller peak signifies the capillary pores. As w/c increases, the curves of the PSD shift to the right, and the area of the gel pore decreases. This is because larger w/c causes larger water content and much less cementitious materials in unit volume, leading to the generation of sparse structure and larger pores. Moreover, the changes in gel pores are more significant at 3 and 7 days than those of 14 and 28 days.  
Figure 3: Distribution of porosity in cement slurries with different w/c ratios.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Sequence** & **TD** & **SW** & **RFD** & **RG1** & **DRG1** & **PRG** & **TW** & **NS** & **NECH** & **TE** & **DL1** \\ \hline FID & 1024 & 200 & 0.005 & 20 & 3 & 2 & 2000 & 4 & — & — & — \\ \hline CPMG & AUTO & 333.33 & 0.005 & 10 & 3 & 2 & 200 & 4 & 4000 & 0.36 & 500 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Configuration of low-field nuclear magnetic resonance parameters.  
Figure 4 illustrates the most probable pore diameter (MPPD, corresponding to the left peak) under different w/c ratios. The MPPD grows as the w/c ratio rises. Furthermore, higher w/c ratios result in more pronounced changes in the MPPD. For example, in the case of WC30, the MPPD decreases by 0.8 nm from 3 to 28 days, while for WC35 and WC40, the reductions are 1.0 nm and 2.0 nm, respectively. A higher w/c ratio may lead to a coarser pore size distribution in the paste, reflected in more significant changes in pore diameter trends. This trend highlights that controlling the w/c ratio is not only crucial for optimizing the early-stage performance of cement-based materials but also plays a vital role in enhancing their long-term durability and density.  
Figure 5 illustrates the variation in the MPPD over time. As shown in the figure, the MPPD increases with a higher w/c ratio at the same age. However, as the curing age progresses, the MPPD generally decreases for all neat cement paste samples. This change is primarily attributed to the ongoing hydration reaction, which generates more hydration products and results in a denser pore structure. Moreover, the difference in the MPPD between samples with different w/c ratios gradually diminishes as the curing age increases. For example, at 3 days and 28 days, the difference in the MPPD between WC40 and WC30 is 2.5 nm and 1.1 nm, respectively. Additionally, the rate of decrease in pore diameter varies significantly between different w/c ratios. The decrease rate of WC40 from 3 days to 28 days is 0.08 nm/day, whereas the decrease rate of WC35 and WC30 are 0.04 nm/day and 0.02 nm/day, respectively.