# pH Measurement of Cement-Based Materials: The Effect of Particle Size
## 3 Results and Discussion
### Possibility of Using Samples with Large Particle Sizes in Measuring pH
#### 3.2.1 Effect of Solid-to-Solvent Ratio on pH  
The effect of solid-to-solvent ratio for large particles was determined. Large particle sizes refer to particles larger than 600 \(\upmu\)m, while fine particle sizes refer to particles smaller than 600 \(\upmu\)m. The solid-to-solvent ratio was changed from 1:2 to 1:1, where 20 g of solid was mixed with 20 g of fresh distilled water. On the same day, and with the same batch of specimens, samples with a size of 300-600 \(\upmu\)m were tested according to the benchmark methodology for reference (Figure 2). The measured pH of 12.35 \(\pm\) 0.02 matched the results reported in Section 3.1.  
Figure 5: Effect of particle size.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Particle Size**} & \multicolumn{3}{c}{**pH Value**} \\ \cline{2-4}  & **In This Study** & **[PERSON] et al. [25]** & **[PERSON] and [PERSON] [19]** \\  & **(Mortar)** & **(Paste)** & **(Concrete)** \\ \hline
2.36–4.75 mm & 12.16 \(\pm\) 0.04 & N.A. & 12.53 \\
1.18–2.36 mm & 12.24 \(\pm\) 0.02 & N.A. & 12.64 \\
600 \(\upmu\)m-1.18 mm & 12.27 \(\pm\) 0.05 & N.A. & 12.72 \\
300–600 \(\upmu\)m & 12.37 \(\pm\) 0.02 & 12.73 & 12.74 \\
150–300 \(\upmu\)m & 12.35 \(\pm\) 0.02 & 12.73 & 12.77 \\ \textless{150} \(\upmu\)m & 12.37 \(\pm\) 0.04 & 12.77 & 12.79 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison for pH among mortar, paste and concrete samples with similar particle sizes.  
Table 4 shows the pH test results of three different ranges of large particle sizes (large particle sizes in ranges I, II and III) with the solid-to-solvent ratio of 1:1 in comparison with the pH value of fine particle sizes with the solid-to-solvent ratio of 1:2. With increasing solid-to-solvent ratio of the large particle sizes, the pH value of the range III particle size is similar to the reference, whereas that of the range II particle size differs from the reference. A meaningful difference was found between the range I particle size and the reference. By increasing the quantity of solid in the same amount of solvent, the total surface area increases, and a higher pH value (equal or close) than the reference could be achieved.  
Figure 6 shows the pH values of the three ranges of large particle size with different solid-to-solvent ratios. The pH increased by about 0.07 units when the quantity of the solid samples was doubled for all the three ranges of the large particle size. [PERSON] et al. (2013) reported that when the solid-to-solvent ratio of ground cement paste was changed from 1:2 to 1:1 (with 20 g of water), the pH increased by about 0.05 units. [PERSON] and [PERSON] (2019) tested the solid-to-solvent ratio for 7-day-old normal-strength concrete (NSC-7) and 180-day-old high-strength concrete (HSC-180), which were ground into powder. When the solid-to-solvent ratio was increased from 1:2 to 1:1, the pH value increased by approximately 0.04 units for NSC-7 and 0.12 units for HSC-180. The change in the solid-to-solvent ratio from 1:2 to 1:1 did not contribute much to the pH increment compared with the large particle sizes tested.