Enhancing mechanical properties and crack resistance of high-strength SHCC/ECC for durable transportation through ethylene-vinyl acetate polymer modification

Strain-hardening cementitious composites (SHCC) possess excellent ductility and toughness, making them suitable for reinforcement and repair projects of transit infrastructures, such as tunnel linings, bridges, and highways. Especially, polyethylene (PE) fiber is admixed to SHCC for fabricating high-strength PE-SHCC. However, the hydrophobic nature of PE fibers results in relatively weak interfacial frictional bond strength with cementitious matrix, ultimately leading to larger crack widths and wider gaps. This poses durability and safety concerns for the practical applications of PE-SHCC in transit infrastructure. In this study, ethylene-vinyl acetate (EVA) dispersible polymer is selected to address this problem. The effect of admixing EVA on mechanical and direct tensile properties of PE-SHCC is investigated. The compressive strength, first crack strength and matrix fracture toughness of PE-SHCC tended to decrease after EVA modification, however, the tensile strength and tensile strain increased significantly with doping. After that, the single fiber pullout test combined with flaw size/distribution analysis is performed to explore the improvement mechanism of PE-SHCC after EVA modification. It was found that the addition of EVA could significantly improve the interfacial transition zone (ITZ), increase the interfacial friction between PE fibers and matrix, and optimise the defect distribution within the matrix. The recommended dosage of EVA is 3–6 % comprehensive consideration of the tensile strength, strain energy, crack width, and mechanical strengths of the EVA-modified PE-SHCC. The enhancement of mechanical strengths and crack resistance in PE-SHCC contributes to the development of transit infrastructure towards greater reliability, durability, and resilience.