## 4 Conclusions  
The mechanical properties of spun pile materials decrease due to corrosion attacks. This study comprehensively discussed the corrosion effect on the mechanical properties of spun pile materials using a 3D FEA. Additionally, the deterioration degrees of the concrete compressive strength, yield strength of PC-bar, and bond strength between PC-bar and concrete were investigated following the corrosion degree. The following conclusions were drawn from this study:  
1. The diameter of the rebar affects the magnitude of the rust thickness. At the same corrosion degree, the rust thickness that occurred on the transverse rebar was more significant than the rust on the PC-bar.
2. The nonuniform rust distribution exerts an internal pressure on the outer side of the spun pile and influences the crack distribution in a spun pile section. As a result, interconnection cracks were predicted to form along the PC-bars at a corrosion degree larger than 10%. Cover concrete spalling was anticipated after the corrosion degree reached 14.74%.
3. The nonuniform rust distribution caused a significant compressive strength reduction in the cover concrete compared to the core concrete, primarily at corrosion degrees  
Figure 16: Relationship between corrosion degree and yield strength reduction ratio.  
Figure 15: PC-bar stress–strain relationship.  
larger than 12%. The proposed equations successfully predicted the decline of the concrete compressive strength for the cover and core concrete. In contrast, the previous study's equation slightly underestimated the core concrete compressive strength reduction. In addition, it significantly overestimated the cover concrete compressive strength reduction in the extensive corrosion degree range.
4. The bond strength was reduced inverse-exponentially against the corrosion degree due to cracks in the concrete around the corroded rebar. The proposed equation could predict the bond strength decrease precisely, while the equations proposed by previous studies overestimated or underestimated the FEA results.
5. The yield strength of the PC-bar was reduced linearly against the corrosion degree. The equation to predict the yield strength reduction ratio was proposed and was found in line with that suggested by a previous study.  
Conceptualization, A.N.R. and T.N.; methodology, A.N.R. and T.N.; software, A.N.R.; validation, A.N.R. and T.N.; formal analysis, A.N.R. and T.N.; investigation, A.N.R. and T.N.; resources, A.N.R. and T.N.; data curation, A.N.R.; writing--original draft preparation, A.N.R.; writing--review and editing, T.N.; visualization, A.N.R.; supervision, T.N.; project administration, A.N.R.; funding acquisition, A.N.R. All authors have read and agreed to the published version of the manuscript.  
This research was funded by PT. Inti Teknik Solusi Cemerlang (ITSC), grant number 037/ADM.ITSC/VIII/2019, and the APC was funded by PT. ITSC.  
Not applicable.  
The datasets generated and/or analysed during the current study are available from the corresponding author upon reasonable request.  
The authors would like to express their gratitude to [PERSON] from Institut Teknologi Sepuluh November for providing the 3D-NLFEA software package.  
The authors declare no conflict of interest.