## 3 Results and Discussion  
### Strengths Characteristics  
Figure 3(a),b represent the results of the compressive and flexural strength tests for each specimen ID, respectively, including statistical analysis results such as average (Avg. ), standard deviation (Std. ), and \(p\)-values from \(t\)-test results. It was observed that specimens additionally cured in the 30% strontium nitrate solution exhibited improved compressive and flexural strengths compared to those cured in water for the same period. For compressive strength, the H1 specimen showed 24.25 MPa, while S1 exhibited a higher value of 27.98 MPa, which is approximately 15.4% greater. The compressive strength of S3 was 28.67 MPa, which is about 13.3% higher than the 25.31 MPa of H3. After 7 days of treatment with the strontium nitrate solution, S7 showed a compressive strength of 29.13 MPa, which is about 9.3% higher than H7 (26.66 MPa). Based on the results of the F-test for H groups and S groups, the two groups were assumed to have equal variances, and a \(t\)-test was conducted accordingly. For the results of the compressive strength tests, in the case of H3 and S3, the \(p\)-value was 0.0785, indicating a confidence level of approximately 92%. However, for 'H1 and S1' as well as 'H7' and S7', the \(p\)-values were significantly lower, suggesting that the differences in mean values are highly significant. The strength increase due to the strontium nitrate solution treatment was more pronounced in flexural strength than in compressive strength. The flexural strength of S1 was 7.932 MPa, which is approximately 73.0% higher than the 4.584 MPa of H1. For S3, a value of 8.684 MPa was measured, which is about 73.8% greater than the 4.824 MPa of H3. The flexural strength of S7 was 8.683 MPa, which is about 65.7% higher than the 5.240 MPa of H7. For the flexural strength tests, the \(t\)-test analysis results indicate a high level of confidence in the difference in mean values between the two groups. While specimens additionally cured in deionized water did not show a significant increase in strength within the error range over the 7-day treatment  
Figure 3: Test setup. period, those cured in the strontium nitrate solution demonstrated considerable strength enhancement, especially in the early stages of the treatment. Figure 4(a),b show the cross-sections of the flexural strength specimens S1 and S7, respectively. The penetration of the 30% strontium nitrate solution through the surface of the specimens can be clearly observed. The penetration depth was measured to be approximately 2.5-5.0 mm for the S1 specimen, which was immersed for a shorter duration, and about 3.5-6.5 mm for the S7 specimen, which was immersed in the strontium nitrate solution for 6 days longer than S1. Despite this extended immersion, the increase in penetration depth was only in the range of 1.0-1.5 mm, suggesting that most of the penetration occurs during the early stage of immersion. This observation likely explains the more significant increase in compressive and flexural strengths observed in the early stages of the treatment. Figure 5(a) depicts one selected load-deflection curve from the flexural strength tests of specimens H7 and S7, along with DIC analysis images at 20 Hz showing the distribution of maximum principal stress just before failure. The maximum deflection at failure for the H7 specimen was measured to be 0.042 mm, while for the S7 specimen, it was 0.047 mm. Relative to these deflection values, a significantly higher failure load was recorded for the S7 specimen. Additionally, it was observed that specimens additionally cured in the 30% strontium nitrate solution exhibited characteristics of a brittle failure mode compared to those cured in deionized water for the same period. Initially, both H7 and S7 specimens exhibited similar load-deflection curve slopes, but after exceeding a deflection of 0.01 mm,  
Figure 4: Results of strength tests. Figure 5: Penetration depth of strontium nitrate aqueous solution. the slope for H7 became more gradual compared to that for S7.