Effect of modified PE fiber grafted with nano-SiO2 on the tensile properties of high-strength engineering cementitious composites

PE fibers are widely employed in the fabrication of high-strength engineering cementitious composites (HSECC). However, the inherent hydrophobic state of the fiber surface weakens the fiber-matrix interfacial transition zone (ITZ). In this study, a method for modifying the fiber surface is proposed that involves utilizing silane coupling agent (SCA) as a second-stage modification bridge, with the fiber surface being coated through the sol-gel method to form a layer of nano-SiO2. This modification strategy enhances the ITZ and improves the tensile performance of HSECC. The results show that the fibers are uniformly wrapped by SCA and the nano-SiO2 is effectively grafted onto the -NH2 sites within SCA molecule. The application of the SCA and nano-SiO2 coating alleviates the hydrophobicity of PE fiber surface, and effectively enhances the interfacial bonding energy, interfacial friction stress, and pull-out energy between the fibers and matrix. Specifically, the fibers after second modification increase the ultimate tensile strength and tensile strain performance of HSECC by 28.9% and 168.4% respectively, while reducing the crack width and increasing the number of cracks. Based on this new modification method, the properties of PE fibers are effectively utilized and the strain hardening behavior of HSECC is optimized.