Investigation on energy dissipation characteristics and stress-strain relationship models of PVA fiber-oriented enhanced ECC under compressive and tensile loading

To more accurately reveal the failure behavior of engineered cementitious composites (ECC), this study adopts a stress-strain relationship and energy evolution perspective, using uniaxial compression and tensile tests to explore the mechanical properties of ECC under different casting methods. The influence of PVA fiber orientation on ECC's strain hardening and failure process was analyzed, and stress-strain models were developed for different casting methods and fiber contents. The internal energy evolution was analyzed, and fiber orientation was quantitatively assessed using image analysis and CT measurements. Pore characteristics of ECC were evaluated through MIP and CT 3D reconstruction. Oriented samples showed higher tensile strain in the strain hardening stage, with the tensile strain of O2 increasing from 3.92 % in R2 to 5.18 %, compared to randomly cast specimens. Directed casting significantly improved compressive strength, energy release rate, and dissipation capacity, enhancing the tensile performance, elastic strain energy, and fracture energy of ECC. The stress-strain relationship model demonstrated a strong correlation, offering valuable insight for optimizing and applying ECC's performance in engineering. Furthermore, the fluorescent immersion method showed that the fiber inclination angles of oriented casting samples ranged from 20° to 40°, with an orientation factor of 0.85, compared to below 0.75 for randomly cast samples. CT scans confirmed that PVA fibers in oriented casting aligned with the tensile direction, significantly increasing in quantity. MIP analysis revealed that most PVA-ECC pores were smaller than 100 nm, primarily in gel and transition pores, with higher sphericity and more regular shapes.