Water conservancy structures are susceptible to hydraulic cracking under prolonged water pressure, posing a significant threat to structural safety. Consequently, improving the crack resistance of construction materials is essential. Engineered cementitious composites (ECC), with their superior toughness and excellent crack control, have strong potential as a replacement for conventional concrete. However, the mixed-mode I-II fracture behavior of ECC under hydraulic–mechanical coupling remains insufficiently understood and requires further investigation. In this study, four-point bending beam specimens with prefabricated cracks were prepared. Mixed-mode I-II fracture tests were conducted using a self-designed sealing device under five water pressure levels (0, 0.1, 0.2, 0.3, and 0.4 MPa) and three notch depth ratios (0.2, 0.3, and 0.4). The effects of these parameters on crack initiation load, peak load, fracture energy, and ductility of ECC were systematically analyzed. The distribution of water pressure on the fracture surface is assumed to be triangular. Under a water pressure of 0.4 MPa, increasing the notch depth ratio from 0.2 to 0.4 causes the crack initiation load and peak load to decrease by 45.23% and 22.40%, respectively, while the fracture energy and ductility increase by 56.30% and 101.80%. This behavior results from the crack-bridging effect of PVA (Polyvinyl alcohol) fibers, which enhances shear resistance. However, as the notch depth ratio increases, the fracture surface area and the number of fibers resisting crack propagation decrease, leading to reduced load-bearing capacity. When the notch depth ratio is 0.4, increasing the water pressure from 0 to 0.4 MPa leads to reductions in crack initiation load (Pini), peak load (Pmax), and fracture energy (Gf) by 54.02%, 35.04%, and 13.23%, respectively, while ductility increases by 34.39%. This phenomenon can be explained by the influence of water pressure on the fracture process and the energy dissipation mechanism of ECC. Specifically, water pressure weakens the effective confining stress, reducing interfacial bonding and frictional resistance, which leads to a decrease in load-bearing capacity and fracture energy, but an enhancement of ductility at the macroscopic level. A predictive model describing the relationship between water pressure and fracture energy was established, enabling the estimation of ECC fracture performance under various water pressure conditions in practical engineering. The study also reveals the complex mechanical response of ECC under the combined effects of notch depth ratio and water pressure, providing a theoretical foundation and design guidance for its application in water conservancy projects and related fields. However, due to experimental limitations, the specimens used in this study were small. Future work could consider larger specimens and higher water pressures to further validate and extend the findings. Graphical abstract

Effect of hydraulic-mechanical coupling on mixed-mode I-II fracture performance of ECC using a modified pre-cracked four-point bending beam test

期刊论文
发表日期：

2026年7月1日

查看全文

Shuling Gao,
Jiahui Liu,
Haitao Cui,
Longbang Qing

摘要

Water conservancy structures are susceptible to hydraulic cracking under prolonged water pressure, posing a significant threat to structural safety. Consequently, improving the crack resistance of construction materials is essential. Engineered cementitious composites (ECC), with their superior toughness and excellent crack control, have strong potential as a replacement for conventional concrete. However, the mixed-mode I-II fracture behavior of ECC under hydraulic–mechanical coupling remains insufficiently understood and requires further investigation. In this study, four-point bending beam specimens with prefabricated cracks were prepared. Mixed-mode I-II fracture tests were conducted using a self-designed sealing device under five water pressure levels (0, 0.1, 0.2, 0.3, and 0.4 MPa) and three notch depth ratios (0.2, 0.3, and 0.4). The effects of these parameters on crack initiation load, peak load, fracture energy, and ductility of ECC were systematically analyzed. The distribution of water pressure on the fracture surface is assumed to be triangular. Under a water pressure of 0.4 MPa, increasing the notch depth ratio from 0.2 to 0.4 causes the crack initiation load and peak load to decrease by 45.23% and 22.40%, respectively, while the fracture energy and ductility increase by 56.30% and 101.80%. This behavior results from the crack-bridging effect of PVA (Polyvinyl alcohol) fibers, which enhances shear resistance. However, as the notch depth ratio increases, the fracture surface area and the number of fibers resisting crack propagation decrease, leading to reduced load-bearing capacity. When the notch depth ratio is 0.4, increasing the water pressure from 0 to 0.4 MPa leads to reductions in crack initiation load (P_ini), peak load (P_max), and fracture energy (G_f) by 54.02%, 35.04%, and 13.23%, respectively, while ductility increases by 34.39%. This phenomenon can be explained by the influence of water pressure on the fracture process and the energy dissipation mechanism of ECC. Specifically, water pressure weakens the effective confining stress, reducing interfacial bonding and frictional resistance, which leads to a decrease in load-bearing capacity and fracture energy, but an enhancement of ductility at the macroscopic level. A predictive model describing the relationship between water pressure and fracture energy was established, enabling the estimation of ECC fracture performance under various water pressure conditions in practical engineering. The study also reveals the complex mechanical response of ECC under the combined effects of notch depth ratio and water pressure, providing a theoretical foundation and design guidance for its application in water conservancy projects and related fields. However, due to experimental limitations, the specimens used in this study were small. Future work could consider larger specimens and higher water pressures to further validate and extend the findings.

Graphical abstract