Mechanical Behavior and Interface Micromechanics of ECC Reinforced with Oriented PVA Fibers

Fiber distribution is a critical factor influencing the strain hardening and multiple cracking behavior of engineered cementitious composites (ECC). However, polyvinyl alcohol (PVA) fibers are considered “soft fibers,” making it challenging to achieve an ideal uniform distribution, an essential scientific issue requiring urgent attention. This paper examines the impact of traditional versus directional pouring methods and fiber content on the mechanical properties of ECC. A fluorescent soaking method for PVA fibers was developed, and the orientation distribution of PVA fibers was analyzed using the image processing software Image J. The microstructure and pore characteristics of ECC were analyzed using microscopy, mercury intrusion porosimetry, atomic force microscopy (AFM), and nanoindentation (NT) to reveal the influence mechanism of pouring methods and fiber content on its micromechanical properties. Results indicate that when PVA fiber content is 2%, the compressive strength of PVA-ECC under the directional pouring method increases by 2.86% compared to random pouring. Additionally, the tensile strength and tensile strain improve by 6.6% and 32.1%, respectively, while the fiber orientation coefficient rises by 34.0%. AFM and NT studies show that ECC prepared with directional pouring has a flatter surface morphology, more stable mechanical properties in the matrix phase, and an increased elastic modulus in the PVA fiber-matrix interfacial transition zone. Thus, the directional pouring device enhances fiber bridging efficiency in PVA-ECC and may also serve as a reference for directional methods with soft fibers, such as polypropylene and polyethylene fibers.