## 3 Results and Discussion
### Range Analysis and Analysis of Variance
#### 3.3.3 Range Analysis and ANOVA of Flexural Strength  
Table 13 lists the mean S/N ratio at each level of the experimental control factors of the flexural strength and Figure 13 shows the S/N response graph of the flexural strength. As can be seen from Table 13 and Figure 13, the fine aggregate content was the significant factor in controlling the flexural strength, and when the fine aggregate content is 10%, the response value was the largest. It can be seen from Figure 13 that the general trend was that the flexural strength increased almost linearly with the increase in the percentage of fine aggregate.  
Figure 11: The S/N response graph for the elastic modulus of the LPC.  
Figure 12: Relationship between the elastic modulus and void ratio.  
In addition, it can be seen from Figure 14 that the relationship between the flexural strength and void ratio was roughly inversely proportional, irrespective of any coarse aggregate size. In engineering practice, fine aggregate can be added to the PC mixture, usually within 5-10% of the mass of coarse aggregate, to improve strength and durability [78]. Research by [PERSON] et al. [79] showed that adding 10% river sand to a PC mixture with a water-cement ratio of 0.3-0.4 resulted in a slight decrease in porosity (about 12%) and an increase in compressive strength by 50%. [PERSON] and [PERSON] [80] added 7% by mass of coarse aggregate sand to recycled aggregate and high-porosity PC (>50%) with a water-cement ratio of 0.27, resulting in a 16% reduction in porosity and a 19% increase in compressive strength. The above results show that sand can reduce the porosity, provide a thicker paste coating, and increase the contact area between the aggregates, further improving the interlocking of the aggregates, thereby increasing the strength of the PC [77]. As the compressive strength increased, the flexural strength also improved. In addition, the ANOVA and \(F\) test results in Table 14 show that the fine aggregate content had the maximum contribution to the LPC mixture toward the flexural strength. The contribution percentage of fine aggregate content with respect to the flexural strength of the LPC mixture was 46.00%, which was the maximum among all the factors, followed by the matrix type (38.28%), and then by the aggregate-to-binder ratio (13.35%). According to the above results, the optimal combination level of the experimental control factors for achieving the maximum flexural strength was A\({}_{1}\)B\({}_{3}\)C\({}_{1}\)D\({}_{2}\), i.e., the coarse aggregate size at level 1, fine aggregate content at level 3, matrix type at level 1, and aggregate to binder ratio at level 2.  
Figure 14: Relationship between the flexural strength and void ratio.  
Figure 13: The S/N response graph for the flexural strength of the LPC.  
Moreover, the ANOVA and \(F\) test results in Table 14 also confirmed that the fine aggregate content was the most important factor affecting the splitting tensile strength of the LPC. The contribution percentages of these factors were fine aggregate content (87.20%), coarse aggregate size (8.15%), and matrix type (4.12%). According to the results of the S/N ratio and the analysis of variance, the optimal combination level of the experimental control factors for achieving maximum splitting tensile strength was A\({}_{3}\)B\({}_{3}\)C\({}_{1}\)D\({}_{1}\), i.e., the coarse aggregate size at level 3, fine aggregate content at level 3, matrix type at level 1, and aggregate to binder ratio at level 1.