3D printing performance of strain-hardening cementitious composites with different UHMWPE fibers in correlation with rheology

The Strain-Hardening Cementitious Composites (SHCC) have been studied for 3D concrete printing (3DCP) due to their promising ductility under tensile loads. The issues regarding clogging of incorporated fibers in SHCC during extrusion and 3D printing limit their further application in 3DCP. Instead of bulk volume inspection of SHCC compositions, the rheology can be studied on a small scale to monitor the SHCC buildability and extrudability. The UHMWPE fibers were first modified to increase their hydrophilicity, so that the contribution of hydrophobic as well as hydrophilic fibers could be studied together. The effects of water/binder ratio and nanoclay dosage were also explored. A constant shear rate protocol was employed to observe shear stress decay for various compositions of fresh SHCC. The thixotropy index ( I thix ), static and dynamic yield stresses for 3D printable SHCC were found appropriate to evaluate structure-property relation. Subsequently, 3DCP of the selected SHCC compositions using hydrophobic and hydrophilic fibers further confirmed their 3DCP performance. SHCC with hydrophilic fibers bearing lower dynamic yield stress were easily extrudable as compared to SHCC with hydrophobic fibers exhibiting relatively higher dynamic yield stress. However, higher static yield stress in SHCC with hydrophobic fibers could facilitate the SHCC buildability which was slightly poor in SHCC with hydrophilic fibers. Thus, rheology could indirectly explain the flow properties of SHCC mixture appropriate for 3DCP. Further, the mechanical performance under uniaxial tensile load revealed stronger strength in SHCC with hydrophilic fibers, enhancing first-cracking strength by 47.83 % and ultimate tensile strength by 12.68 %, although reducing the ductility up to 50.60 %. Consequently, 3DCP for SHCC with hydrophobic/hydrophilic fibers was evaluated considering their rheology and tensile properties. • 3DCP of SHCC reinforced with hydrophobic/hydrophilic UHMWPE fibers. • Rheological evaluation of fresh SHCC for 3DCP using constant shear rate tests. • Greater I thix (high static τ y and low dynamic τ e yield stresses) for good 3DCP. • Hydrophilic fibers enhance SHCC tensile strength more than that of hydrophobic ones. • First-cracking and ultimate tensile strengths rise 47.83 % and 12.68 %, respectively.