Effect of PE fiber coated by polydopamine and nano-SiO2 on the strain hardening behavior of ultra-high-strength and high-ductility cementitious composites

Abstract

Ultra-high molecular weight polyethylene (PE) fiber with startling mechanical properties and elastic modulus is considered an ideal reinforcing component for Ultra-High-Strength and High-Ductility Cementitious Composites (UHS-HDCCs). However, the fiber/matrix interfacial bonding is weakened due to the hydrophobic nature of the PE fiber surface, restricting the perfect expression of the PE fiber inherent characteristics. In this work, a promising technology for PE fiber surface functionalization using a combination of bio-inspired polydopamine (PDA) and deposited nano-SiO2 was proposed to enhance the fiber/matrix interfacial bonding in UHS-HDCCs. The results showed that PDA produced a uniform coating on the surface of PE fiber, and nano-SiO2 was successfully grafted to the surface of PE fiber through PDA coating as a bridge. The PDA and nano-SiO2 coatings introduced hydrophilic functional groups on the PE fiber surface, thereby enhancing the wettability of the PE fiber surface. The SiO2-PDA-PE fibers improved the ultimate tensile stress and tensile strain capacity of UHS-HDCCs to 117.1% and 130.2% respectively, compared to that of UHS-HDCCs incorporating pristine PE fiber. Furthermore, the SiO2-PDA-PE fibers effectively reduced the crack width and crack spacing while increasing the number of cracks and energy absorption capacity of UHS-HDCCs when subjected to increasing uniaxial tensile loading. The single fiber pullout results showed that both PDA-PE fibers and SiO2-PDA-PE fibers enhanced the peak force, chemical bond, frictional bonding stress, slip hardening coefficient, and pullout energy. Obviously, the positive effect of SiO2-PDA-PE fibers on the critical parameters of the fiber/matrix interface is higher than that of PDA-PE fibers except for the chemical bond. This work explored a novel way to modify the physicochemical performance of PE fiber surfaces for matching the strain hardening behavior of UHS-HDCCs, which is meant to guide the mix-design optimization of UHS-HDCCs.