## 3 Experimental Procedures
### Results and Discussion  
Table 7 indicates the axial compression test data for the specimens. The results of the test were reasonable and were consistent with the related studies [9; 10; 11; 20; 25]. Hence, the correctness of the axial compression test on the specimens was verified. According to the objective of this test, the test results were compared to verify the reinforcement effect  
Figure 11: Load–strain curves of the specimens. Figure 10: Load–displacement curves of the specimens. of the IPCSAM and to analyze the impacts of the reinforcement parameters on the axial compression performance of the strengthened specimens. 1. The strengthening effect of the IPCSAM: The comparison of the test results showed that the peak loads of strengthened specimens S1-A, S1-S, S1-SS, and S2-S2 increased by 91%, 132%, 73%, and 137%, respectively, while the peak strains increased by 58%, 32%, 27%, and 61%, respectively. This meant the bearing capacity and ductility of the strengthened specimens had been significantly improved when compared with the unreinforced specimens, while the strengthening effect of the IPCSAM was remarkable. 2. The influence of the LCSS on the strengthening effect: Since the existing relevant research results are very limited, the results from this paper were only compared with [9]. The comparison of specimen S1-A with the specimen YZ-SS strengthened by the PCSAM [9] showed that for S1-A, the ratio of the cross-sectional area before and after strengthening was A1a = 2.69, the ratio of the bearing capacity before and after strengthening was B1a = 1.91, and the strengthening efficiency was E1p= B1a/A1a= 0.71; for YZ-SS, the ratio of the cross-sectional area before and after strengthening was Ass = 1.96, the ratio of the bearing capacity before and after strengthening was Bss = 1.28, and the strengthening efficiency was Ess = Bss/Ass = 0.65. In other words, the strengthening efficiency increased by 9% using the LCSS instead of the sleeve formed by wire ropes. At the same time, the peak strain of S1-A was also larger than that of YZ-SS, showing the better ductility of S1-A than that of YZ-SS. 3. The influence of the SSAWC on the strengthening effect: The comparison between the two specimens S1-A and S1-S showed that the self-stress increased the bearing capacity by 41%. For S1-S, the ratio of the bearing capacity before and after strengthening was A1s = 2.69, the ratio of the bearing capacity before and after strengthening was B1z = 2.32, and the strengthening efficiency was E1z = 0.86. In other words, the strengthening efficiency increased by 21% using the SSAWC as filled concrete. The reason was that the self-stress produced by SSAWC caused the column to be compressed in three directions, improving the bearing capacity and stiffness. At the same time, the first crack appeared on the interface between the filled concrete, the column of S1-A, and the segment of S1-S specimen. This indicated that self-stress could compensate for the shrinkage of the filled concrete and also contributed to the initial stress on the interface between the filled concrete and adjacent components, improving the bond strength as well as delaying the occurrence of interfacial cracks. Therefore, the SSAWC had significant effects on improving not only the bearing capacity and rigidity of the specimen but also the bond strength. 4. The influence of the strength of the LCSS concrete on the strengthening effect: It was observed from the comparison of S1-S and S1-SS that the reduction of the LCSS concrete strength would directly affect the bearing capacity and peak strain of the strengthened specimen. This was because the LCSS was a component of the strengthened specimen; as the concrete strength of the LCSS was reduced, the load borne by the LCSS was also decreased. At the same time, the lower the concrete strength of the LCSS, the easier the sleeve failed. As such, the self-stress would be reduced due