This article presents a review of the current solutions for the rheological challenge of three-dimensional concrete printing (3DCP), providing a rheological definition for printability, and an overview of the current techniques for obtaining a printable concrete, placing special emphasis on understanding structural build-up and the current mixture proportions and admixtures used to improve it. A promising alternative for improving structural build-up is the use of entrained air (EA), as bubbles, whose effects are reviewed in generic yield stress fluids and then specifically in concrete. After revision of micromechanical models and experimental trials from literature on yield stress fluid bubble suspensions and concrete, EA appears to be ideal for 3DCP when generated by anionic surfactants, as it increases static yield stress and decreases plastic viscosity. Cationic surfactants, however, maintain or slightly decrease static yield stress. It is proposed that the lubricating or stiffening property of the bubbles determines their ability to deform under the shear stress generated by the surrounding fluid. The ability to deform depends on the surfactant used to entrain the bubbles and the mixture design of the concrete. Further experimental research must be carried out for the advantages of EA to be fully realized.

中文翻译：

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气泡作为可印刷混凝土的外加剂：夹带空气的流变效应综述

本文回顾了当前应对三维混凝土打印 (3DCP) 流变学挑战的解决方案，提供了可打印性的流变学定义，并概述了当前获得可打印混凝土的技术，特别强调对结构构建的理解-up 和当前的混合比例和用于改进它的外加剂。改善结构堆积的一个有前途的替代方法是使用夹带空气 (EA) 作为气泡，其效果在通用屈服应力流体中进行了审查，然后专门在混凝土中进行了审查。在对微观力学模型进行修改并从有关屈服应力流体气泡悬浮液和混凝土的文献中进行实验试验后，当阴离子表面活性剂产生时，EA 似乎是 3DCP 的理想选择，因为它增加了静态屈服应力并降低了塑性粘度。然而，阳离子表面活性剂维持或略微降低静态屈服应力。有人提出，气泡的润滑或硬化特性决定了它们在周围流体产生的剪切应力下变形的能力。变形能力取决于用于夹带气泡的表面活性剂和混凝土的配合比设计。必须进行进一步的实验研究，才能充分发挥 EA 的优势。变形能力取决于用于夹带气泡的表面活性剂和混凝土的配合比设计。必须进行进一步的实验研究，才能充分发挥 EA 的优势。变形能力取决于用于夹带气泡的表面活性剂和混凝土的配合比设计。必须进行进一步的实验研究，才能充分发挥 EA 的优势。