## 3 Results and Discussion
### Mechanical Test Results  
Figure 6a shows the 28-day compressive strength of printed (P-X/P-Y/P-Z) and cast (M) specimens at different flowabilities. Printed specimens exhibited lower strength than cast ones, especially at low flowability (153 mm): X, Y, and Z direction strengths were 13.9%, 36.7%, and 41.7% lower, respectively. Strength increased with flowability before stabilizing, approaching cast specimen values due to reduced porosity. In addition, printed specimens showed clear anisotropy: X direction strength exceeded Y and Z directions, with Y generally higher than Z. However, exceptions occurred in some groups at low and high flowability levels, where the Z direction strength exceeded the Y direction strength. This phenomenon may be attributed to the interlocking effect of staggered intralayer interfaces at low flowability, which hinders crack propagation. At high flowability, improved interfacial compaction and significantly reduced porosity minimized the strength disparity between the Y and Z directions. Nevertheless, random errors during the loading process could occasionally alter the relative strength relationship between these directions. Figure 6b shows the 28-day flexural strength of printed (P-X/P-X2/P-Y/P-Z) and cast (M) specimens under different flowabilities. The printed specimens exhibited lower strength than the cast ones with marked anisotropy. The Y and Z directions showed significantly higher strength than the X1 and X2 directions, with minimal difference between Y and Z strengths. The X2 direction strength slightly exceeded X1 at medium-high flowability but was lower at low flowability. This behavior stems from fundamental failure mechanisms. In the Y and Z directions, loading primarily engages the bulk material without interface weakness. In contrast, the X1 and X2 directions fail along intralayer and interlayer interfaces, respectively, due to tensile stresses perpendicular to loading (Figure 7). Additionally, while the directional alignment of fibers enhances the tensile  
Figure 6: The 28-day mechanical strength with different flowabilities: (**a**) compressive strength; (**b**) flexural strength; (**c**) interfacial splitting tensile strength. strength and crack resistance of 3 DPC [43], interfacial regions exhibit minimal fiber content. Consequently, the Y and Z directions benefit from increased fiber presence within the bulk matrix, resulting in superior mechanical performance relative to the X1/X2 directions. At low flowability, irregular intralayer interfaces in the X1 direction hinder crack propagation, making X1 stronger than X2. However, at higher flowability, gravity-compacted interlayer interfaces in the X2 direction demonstrate superior strength. Notably, while the Y and Z direction strengths approached cast specimen values (within 5% at 191 mm flowability), the X1 and X2 directions remained below 50% of cast strength even at maximum flowability. These observations corroborate [PERSON] et al. 's findings [7] that interface bonding strength governs 3 DPC mechanical performance, with tensile stresses preferentially propagating cracks along weaker interfaces. The persistent strength deficit in the X1/X2 directions confirms the critical role of interfacial quality in 3 DPC's structural performance. Figure 6c presents the 28-day interfacial splitting tensile strength of printed specimens (C: interlayer, T: intralayer) and cast specimens (M) at different flowabilities. The results reveal that printed specimens exhibited significantly lower strength than cast specimens due to splitting along these weaker interfaces. At low flowability, T showed slightly higher splitting tensile strength than C, attributed to interlocking effects between staggered filaments. As flowability increased, this interlocking diminished, causing C to regain higher strength than T. Both interfacial strengths stabilized at higher flowability but remained substantially lower than M. For instance, at 191 mm, the strengths of C and T were 32.5% and 37.7% lower than M, respectively.