Additive manufacturing of free formed reinforced concrete elements by selective binding with calcium silicate cements

目前，具有优化设计的仿生结构元件很难用传统的制造工艺制造出来。允许自由选择几何形状的附加制造工艺(3D打印)提供了一种很有前途的替代方案。虽然这种工艺目前在许多生产领域都是最先进的，但到目前为止，它们在建筑业中的应用只被考虑在少数研究项目中。本研究项目旨在开发一种新的方法，将外加剂制造工艺应用于混凝土施工。这项研究的重点是创造一种建造自由形式混凝土结构的基本方法和适当的必要材料。所提出的制造工艺&gt；选择性绑定&lt；是狭义上的3D打印方法。薄层的颗粒状材料通过局部引入可流动的材料而选择性地结合在一起，形成一层又一层的固体，这是以前使用计算机设计的。要研究该方法的两种变体：a)在湿法印刷中，施加细骨料层，并通过点引入粘结剂糊剂选择性地结合。B)在选择性活化中，应用了骨料和粘结剂粉末的混合物，并通过引入水来激活水化过程。到目前为止，研究人员只考虑了用于混凝土外加剂制造的挤压过程。这种方法的明显缺点是限制了悬挑段的生产，严重降低了几何设计的自由度。在一个发表的关于生产建筑构件的选择性粘结的项目中，波特兰水泥没有用作粘结剂。然而，由于其几何自由度，选择性结合在构建中具有最大的潜力。为了在混凝土强度、变形和耐久性能方面积累丰富的混凝土技术经验，并确保必要的材料的可用性，建议的研究项目考虑以硅酸钙为基础的粘结剂。此外，计划首次尝试使用3D打印来生产钢筋混凝土构件。所选方法的可行性已在申请人进行的初步测试中得到证明。为了应用选择性粘结方法在高速下生产出分辨率高、尺寸稳定、强度和耐久性高的混凝土单元，还需要进一步的基础研究。

At present, bionically inspired structural elements with an optimized design can only be produced with great difficulty using conventional manufacturing processes. Additive manufacturing processes (3D printing) which permit a large freedom in choice of geometry present a promising alternative. Although such processes are now state of the art in many areas of production, their application in the construction industry has so far only been considered in a small number of research projects. This research project aims at the development of a new method for the application of additive manufacturing processes in concrete construction. The research focusses on the creation of a basic method for the construction of free form concrete structures and the appropriate necessary materials.The proposed manufacturing process >selective binding< is a 3D printing method in the narrower sense. Thin layers of granular material are selectively bound by local introduction of flowable material to form layer by layer a solid which was previously designed using a computer. Two variants of the method are to be investigated: a) In >wet printing< layers of fine aggregate are applied and selectively bound by point introduction of binder paste. b) In >selective activation< a mixture of aggregate and binder powder is applied and the hydration process activated by introducing water.Up to now researchers have only considered the extrusion process for the additive manufacture of concrete elements. This method has the significant disadvantage that the production of overhanging sections is restricted which severely reduces the freedom of geometric design. In the one published project on selective binding for the production of construction elements, Portland cement is not used as a binder. However on account of its geometric freedom, selective binding has the greatest potential for use in construction. In order to build on the wealth of experience in concrete technology in strength, deformation and durability properties of concrete and ensure the availability of the necessary materials, binders based on calcium silicate are considered in the proposed research project. In addition, first attempts in the production of reinforced concrete elements using 3D printing are planned.The feasibility of the chosen approach has been demonstrated in preliminary tests performed by the applicant. Further fundamental research is needed in order to apply the method of selective binding to produce free form concrete elements with high resolution, dimensional stability, strength and durability at a high construction speed.