This study explores the effects of cellulose nanofibrils (CNF), a relatively new type of nanocellulose material, on the rheological and printability characteristics of cementitious mixtures, and the mechanical properties of 3D printed specimens. The rheology of the mortar mixtures with varying ratios of CNF is thoroughly assessed first. Two testing protocols, stress growth test and ramp test, are followed for rotational measurements using a shear rheometer with a building cell and vane motor. Stress growth tests are carried out to quantify the static yield stress of the cementitious mixtures. Ramp tests are conducted to determine dynamic yield stress and plastic viscosity of the mixes using the Bingham visco-plastic material model. As oscillatory measurements, amplitude sweep tests are carried out to determine the viscoelastic properties of the mortar mixes, including storage modulus and critical strain that are found to be essential for buildability. Thermogravimetric analysis (TGA) is conducted to assess the effects of CNF on the hydration characteristics of the mixtures. The printability and the buildability of the mortar mixtures incorporating CNF are assessed using a 3D concrete printer equipped with a 10 mm diameter nozzle and screw pump mechanism. Tensile, flexural, and compressive strength tests are conducted to determine the mechanical properties of 3D printed specimens with varying ratios of CNFs. Scanning electron microscopy (SEM) is used to conduct the microstructural analysis on fractured surfaces of the mechanically tested specimens. Results indicate that adding CNF at least 0.3 wt% of cement has a favorable effect on the rheological properties of cement composites.

中文翻译：

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纤维素纳米纤丝对3D打印水泥复合材料流变学和力学性能的影响


本研究探讨了纤维素纳米纤丝 (CNF)（一种相对新型的纳米纤维素材料）对水泥混合物的流变性和可打印性特性以及 3D 打印样本的机械性能的影响。首先彻底评估具有不同 CNF 比例的砂浆混合物的流变性。遵循两种测试方案：应力增长测试和斜坡测试，使用带有构建单元和叶片电机的剪切流变仪进行旋转测量。进行应力增长测试以量化水泥混合物的静态屈服应力。进行斜坡测试，以确定使用宾厄姆粘塑性材料模型的混合物的动态屈服应力和塑性粘度。作为振荡测量，进行振幅扫描测试以确定砂浆混合物的粘弹性特性，包括对可施工性至关重要的储能模量和临界应变。进行热重分析 (TGA) 以评估 CNF 对混合物水合特性的影响。使用配备 10 毫米直径喷嘴和螺杆泵机构的 3D 混凝土打印机评估含有 CNF 的砂浆混合物的可打印性和可施工性。进行拉伸、弯曲和压缩强度测试，以确定具有不同 CNF 比例的 3D 打印样本的机械性能。扫描电子显微镜（SEM）用于对机械测试样品的断裂表面进行微观结构分析。结果表明，添加至少 0.3 wt% 的 CNF 对水泥复合材料的流变性能有良好的影响。