The rapid growth of interest toward concrete digital fabrication reflects the current aspiration for better, smarter, faster, and greener construction means. Among a broad variety of techniques developed by our community, digital casting presents clear advantages regarding dimensional precision, geometrical freedom, and surface finish of the produced elements. In contrast to robotic slip forming, the usage of digitally fabricated formworks requires simpler equipment. It, however, calls for easily shaped formworks, typically best three-dimensional (3D) printed, for example, by fused deposition modeling. While such molds can be easily fabricated with a wide range of commercially off-the-shelf available 3D printers, a shortcoming is the susceptibility of many polymers to environmental stress cracking, particularly when in contact with high pH solutions typical for cementitious materials. This article confirms the problem posed by this type of environmental stress cracking and presents two very effective means of circumventing it: A silicone coating and cyclic olefin copolymer. Apart from this, in the specific case of counterpressure casting (CPC), hydrostatic pressure must be resisted by a powder bed surrounding the formwork. The efficiency of such beds is examined and a particular mixture of sand and lead is shown to be particularly effective, provided its density is regulated to balance stress principles derived from soil mechanics. Presented applications include the successful CPC of thin prismatic formworks with a concrete height up to 3 m as representative of typical interfloor load-bearing elements. The combination of counterpressure and stress control is shown to be essential for such achievement, highlighting the potential of this approach as a viable member of the concrete digital casting family.

中文翻译：

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克服用于混凝土反压浇注的 FDM 3D 打印模板的环境应力开裂

人们对混凝土数字化制造兴趣的快速增长反映了当前对更好、更智能、更快和更环保的施工方法的渴望。在我们社区开发的多种技术中，数字铸造在生产元件的尺寸精度、几何自由度和表面光洁度方面具有明显优势。与机器人滑动成型相比，使用数字化制造的模板需要更简单的设备。然而，它需要易于成型的模板，通常最好是三维 (3D) 打印的，例如通过熔融沉积建模。虽然可以使用各种现成的商用 3D 打印机轻松制造此类模具，但缺点是许多聚合物对环境应力开裂的敏感性，特别是当与水泥材料典型的高 pH 值溶液接触时。本文证实了此类环境应力开裂带来的问题，并提出了两种非常有效的规避方法：硅树脂涂层和环烯烃共聚物。除此之外，在反压铸造 (CPC) 的特定情况下，模板周围的粉末床必须抵抗静水压力。对此类床的效率进行了检查，并证明沙子和铅的特定混合物特别有效，前提是调节其密度以平衡源自土壤力学的应力原理。展示的应用包括混凝土高度高达 3 m 的薄棱柱模板的成功 CPC，作为典型的楼层间承重元件的代表。