# Experiment and Analytical Model for Pore Structure of Early-Age Composite Cement Pastes by LF-NMR
## 2 Experimental Materials and Methodology  
### Experimental Materials  
PII 52.5 Anhui Wuhu Conch-brand Portland cement was used. The specific surface area of the cement was determined by the gas adsorption method to be 373 m\({}^{2}\)/kg, with a density of 3180 kg/m\({}^{3}\). Additionally, fly ash, silica fume, and slag were incorporated as supplementary cementitious materials, with densities of 2160 kg/m\({}^{3}\), 2200 kg/m\({}^{3}\), and 3056 kg/m\({}^{3}\), respectively. The chemical compositions of the cement and the materials containing cement are summarized in Table 1, highlighting their key chemical characteristics and their potential influence on the performance of cement-based materials. To further characterize the particle properties of these materials, Figure 1 presents scanning electron microscope (SEM) images showing the particle morphology of cement, fly ash, slag, and silica fume. These images clearly illustrate the shape and surface characteristics of the different materials.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Sample** & **CaO** & **SiO2** & **Al2O3** & **Fe2O3** & **MgO** & **K2O** & **Na2O** & **TiO2** & **SO3** \\ \hline Cement & 64.7 & 19.6 & 4.5 & 3.1 & 0.8 & 0.6 & 0.07 & — & — \\ Fly ash & 2.13 & 54.0 & 35.1 & 3.90 & 0.512 & 1.26 & 0.47 & 1.29 & 0.45 \\ Slag & 39.9 & 30.8 & 14.6 & 0.61 & 8.65 & 0.576 & 0.40 & 1.22 & 2.19 \\ Silica fume & 1.40 & 91.4 & 0.61 & 0.88 & 2.37 & 1.68 & 0.43 & — & 0.48 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The chemical makeup of the cement and binder materials (%).  
Figure 1: Raw materials.  
In this study, in order to study the influence of different water-to-cement (w/c) ratios on the pore size distribution (PSD) curve and the most probable pore diameter of cement slurry, the w/c ratios of the neat cement pastes were set to 0.3, 0.35, and 0.4, while the water-to-binder (w/b) ratio for the composite cement pastes was uniformly set to 0.4. The fly ash content was 15% and 30%. The slag content was 15% and 30%, and the silica fume content was 5% and 10%. Table 2 presents the mixture proportions of both neat and composite cement pastes. In this table, WC represents the neat cement pastes, while FA, SL, and SI represent the composite cement pastes blended with fly ash, slag, and silica fume, respectively. For example, WC30 refers to a paste with a w/c ratio of 0.3, while FA15 refers to a composite paste with a w/b ratio of 0.4 and 15% fly ash content.  
The specific steps of this experiment were as follows. The required amounts of cement, water, and additives were accurately measured. After the cement and additives were thoroughly mixed in the planetary mixer, water was gradually added to the cementitious materials in the mixer. Subsequently, the mixture was stirred at a speed of 140 revolutions per minute (rpm) for 1 min to ensure uniform mixing of the materials. Then, the mixing procedure was paused for 30 s to scrape the adhered paste on the sidewall of the mixing container. The paste was cast into a 2 cm \(\times\) 2 cm square mold after another mixing at 285 rpm for 2.5 min. The specimens were sealed for 24 h at room temperature (approximately 20 \({}^{\circ}\)C) before being molded. After being molded, the specimens were sealed for instant curing. Subsequently, the specimens were cured under standard conditions for the prescribed durations of 3, 7, 14, and 28 days.