Rheological Investigations of Fresh Fiber-Reinforced Cementitious Composites Using Hydrophobic / Hydrophilic UHMWPE Fibers for 3D Concrete Printing Evaluation (2025-11)¶

Rheological tests (low-amplitude oscillatory shear, creep and creep recovery, and steady shear rate) were used to evaluate the 3D concrete printing (3DCP) performance of fiber-reinforced cementitious composites (FRCC). UHMWPE fibers were modified to increase hydrophilicity and functionality. FRCC with hydrophilic or hydrophobic fibers, with or without nanoclay, was assessed for extrudability and buildability. Hydrophilic fibers significantly enhanced microstructural rigidity, followed by hydrophobic fibers and nanoclay, evidenced through an increase of storage modulus by 115.29%, 59.37%, and 49.49%, respectively. The combined inclusion of hydrophilic fibers and nanoclay developed the stiffest, strongest, and stable solid-like microstructure with 211.52% enhanced storage modulus, 87.20% lowered creep compliance, 100% elastic recovery, and the highest viscoelastic yield stress, as compared to a simple cement/water mixture. Hydrophobic fibers with nanoclay also improved storage modulus and yield stresses, enabling effective buildability and extrudability. Certain FRCC compositions succeeded in 3DCP extrusion tests due to higher storage modulus and optimal yield stresses. The tensile strength and ductility of printed samples containing hydrophilic fibers improved due to stronger fiber-matrix bonding, as reflected by 40% higher first-crack strength, 19% higher ultimate tensile strength, and 50.27% enhanced strain capacity as compared to samples with hydrophobic fibers. The addition of nanoclay further improved the matrix strength in both cases. However, the ductility of FRCC containing hydrophilic fibers with nanoclay decreases by more than 50% compared to FRCC with only hydrophilic fibers, likely due to insufficient water availability to satisfy the demand of both water-absorbing components in the FRCC system. Overall, FRCC containing hydrophilic fibers without nanoclay is found to be the most effective option for 3DCP performance, demonstrating superior rheological behavior, tensile strength, and ductility.