In 3D concrete printing (3DCP), it is necessary to meet contradicting rheological requirements: high fluidity during pumping and extrusion, and high stability and viscosity at rest to build the layered structure. In this paper, the impact of the hydroxypropyl methylcellulose (HPMC)-based viscosity-modifying admixture (VMA) on the 3D printability and mechanical performance of a limestone and calcined clay based cementitious material is investigated. A combination of VMA and superplasticizer was used for that purpose. In this case, controlling the competitive effects between VMA and superplasticizer becomes critical. The main strategy for 3D printing in this study was to add an optimal dosage of VMA in the solid suspension that was already mixed with water and superplasticizer. A lab-scale 3DCP setup was developed and demonstrated as well. A series of tests was performed to characterize the effects of VMA on flowability, extrudability, open time, buildability, green strength, hydration, compressive strength, and air void content and distribution. Experiments performed in this study showed that the mixture containing 0.24% (of the binder mass) of VMA exhibited satisfactory 3D printability and optimal mechanical performance. Finally, the results, limitations, and perspectives of the current research were discussed.

中文翻译：

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使用增粘剂提高石灰石煅烧粘土基胶凝材料的印刷适性

在 3D 混凝土打印 (3DCP) 中，必须满足相互矛盾的流变要求：泵送和挤出时的高流动性，以及静止时的高稳定性和粘度以构建层状结构。在本文中，研究了基于羟丙基甲基纤维素 (HPMC) 的粘度调节剂 (VMA) 对石灰石和煅烧粘土基胶凝材料的 3D 可打印性和机械性能的影响。为此目的使用了 VMA 和超塑化剂的组合。在这种情况下，控制 VMA 和超塑化剂之间的竞争效应变得至关重要。本研究中 3D 打印的主要策略是在已经与水和超塑化剂混合的固体悬浮液中添加最佳剂量的 VMA。还开发并演示了实验室规模的 3DCP 设置。进行了一系列测试以表征 VMA 对流动性、挤出性、开放时间、可建造性、生坯强度、水合作用、抗压强度以及空隙含量和分布的影响。本研究中进行的实验表明，含有 0.24%（粘合剂质量）VMA 的混合物表现出令人满意的 3D 可打印性和最佳机械性能。最后，讨论了当前研究的结果、局限性和前景。24%（粘合剂质量）的 VMA 表现出令人满意的 3D 可打印性和最佳机械性能。最后，讨论了当前研究的结果、局限性和前景。24%（粘合剂质量）的 VMA 表现出令人满意的 3D 可打印性和最佳机械性能。最后，讨论了当前研究的结果、局限性和前景。