## 3 Results  
### Mechanical Properties  
Figure 3 presents the results of the UCS tests, indicating a positive correlation between sample strength, curing time, and cement content and a negative correlation with IFC. For PCPB samples with cement-to-sand ratios of 1:6 and 1:8, the strength at various IFCs was significantly higher than that of samples with a cement-to-sand ratio of 1:10. Among these, the C8F20 sample achieved the highest strength, reaching 1.41 MPa after 28 days of curing. In the early curing stages, the samples with a cement-to-sand ratio of 1:6 exhibited the highest strength, while those with a 1:10 ratio showed the lowest strength due to lower cement content. This lower content leads to slower hydraulic reactions, more internal free  
Figure 3: The UCS results for samples with varying cement-to-sand ratios: (**a**) 1:6, (**b**) 1:8, and (**c**) 1:10.  
water, and fewer hydration products, hindering early strength development [52]. However, after 28 days of curing, the strength differences between samples with the same IFC but different cement contents became negligible. This suggests that the negative impact of fluorine on strength is most pronounced during early hydration. Conversely, differences in strength between samples with the same cement content but different IFCs increased after 28 days, with higher fluorine content resulting in lower strength. Thus, higher IFCs directly reduce strength, regardless of the cement-to-sand ratio. Figure 4a shows the poor strength of PCPB samples at 7 days of curing, where samples with different cement-to-sand ratios exhibited relatively similar strengths. This suggests that fluorine significantly hinders early hydration, likely due to the inhibition of C3A and C3S dissolution by gypsum in the silicate-based PG cementation system, leading to poor binding ability [53]. At 14 days of curing, as depicted in Figure 4b, samples with a cement-to-sand ratio of 1:6 performed better. By 28 days, as shown in Figure 4c, samples with IFCs of 20 mg and 40 mg and a cement-to-sand ratio of 1:8 performed better. The UCS results indicate that lower IFCs lead to better strength, but in later curing stages, higher cement content does not necessarily correlate with better strength. However, samples with higher fluoride content consistently showed lower strength, even during the later stages of curing. Previous studies have also demonstrated that soluble NaF results in decreased strength after 28 days of curing [23]. In summary, while higher cement content enhances early strength, its benefits diminish over time, particularly in the presence of higher fluoride content. Lower IFCs are critical for achieving better strength in PCPB samples, emphasizing the need for controlling fluoride content in these applications. The latter stages of the reaction of the PCPB cementitious system are the main object of study, and the fitting treatments are centered around 14 days of curing and 28 days of curing; the derived equations describing the relationship between strength, IFC, and cement content were obtained using the IBM(r) SPSS2(r) Statistics software. This study focuses on the later stages of the reaction in the PCPB system, specifically evaluating curing periods of 14 and 28 days. The analysis was conducted using IBM(r) SPSS2(r) Statistics software to derive fitting formula that describes the relationships between strength, IFC, and cement content. The formula describing the behavior of samples after 14 days and 28 days of curing:  
\[U_{14}=0.503-0.251C-0.002I+17.817C^{2}+5.105\times 10^{-6}I^{2}-0.009 CI,\ \text{R}^{2}=0.976 \tag{1}\]  
\[U_{28}=-0.894+32.256C-0.01I-108.074C^{2}+4.546\times 10^{-5}I^{2}+0.007 CI,\ \text{R}^{2}=0.955 \tag{2}\]  
where \(U_{14}\) and \(U_{28}\) are the UCS of PCPB curing in 14 and 28 days, respectively (MPa). \(C\) is the cement-to-sand ratio (wt%), and \(I\) is the IFC (\(1\times 10^{5}\) wt%). Figure 5a presents the response surface curve and contour graph of the UCS results for samples for 14 days of curing.