Abstract
This study investigated the feasibility of using nanofibrilliated celluloses (CNF) (0.1% by weight of binder materials) with three oxidation degrees, no oxidation (NCNF), low oxidation (LCNF), and high oxidation (HCNF), as a viscosity-modifying agent (VMA) to develop polyethylene fiber (PE)-engineered cementitious composites (ECC). Attenuated total reflection-Fourier transform infrared (ATR-FTIR), dynamic light scattering (DLS), and zeta potential were performed to characterize the properties of the CNF with different oxidation degrees. More stable CNF suspensions could be obtained due to the increasing oxidation degree. Rheology tests showed that CNF replacing VMA could modify the plastic viscosity and yield stress of the fresh matrices. With increasing the oxidation degree of CNF, a significant enhancement was seen for the rheological parameters. It was conducted that CNF could increase the compressive strength, the tensile stress, the nominal flexural strength, and the fracture toughness compared with ECC using VMA, and much higher oxidation degrees yielded higher enhancements (HCNF > LCNF > NCNF). ECC using CNF to replace VMA also achieved ultra-high ductility behavior with the tensile strain of over 8% and the saturated multiple cracking pattern. These finds were supplemented by thermal gravimetric analysis (TGA), which showed that the degree of hydration increased with increasing CNF surface oxidation degree. Additionally, the morphology images of PE fibers were observed by scanning electron microscope (SEM).
Highlights
Engineered cementitious composites (ECC) are a type of cement-based materials with high ductility, which belongs to the range of fiber-reinforced cementitious composites (FRC)
When cracks appear under the tensile load, the load is Engineered Cementitious Composites Modified Nanocelluloses transferred from Polyvinyl alcohol (PVA) fibers to the surrounding matrices, and fibers rupture due to the existence of the chemical bond during the debonding process of PVA fibers
Compared with PVA fibers, the surface of PE fibers is hydrophobic and has higher nominal tensile strength and nominal tensile modulus of elasticity, and PE fibers embedded in matrices have a higher bridging ability (Wang et al, 2020b), breaking through the limitations of PVA-ECC
Summary
Engineered cementitious composites (ECC) are a type of cement-based materials with high ductility, which belongs to the range of fiber-reinforced cementitious composites (FRC). The energy generated by the ruptures of fibers is less than that generated by the sliding friction of fibers (Pereira et al, 2012), weakening the bridging ability of PVA fibers, thereby limiting the improvement of the strength and ductility of ECC. Compared with PVA fibers, the surface of PE fibers is hydrophobic and has higher nominal tensile strength and nominal tensile modulus of elasticity, and PE fibers embedded in matrices have a higher bridging ability (Wang et al, 2020b), breaking through the limitations of PVA-ECC. The rheological properties of the fresh ECC matrices affect strongly the fiber dispersion uniformity, and it is necessary for combining rheology with ECC micro-design theory to achieve the high ductility of cementitious composites (Li and Li, 2013)
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