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

目前，采用传统的制造工艺很难生产出具有优化设计的仿生结构元件。增材制造工艺（3D打印）允许很大的自由选择几何呈现一个有希望的替代方案。虽然这种工艺现在在许多生产领域都是最先进的，但迄今为止，它们在建筑工业中的应用只在少数研究项目中得到考虑。本研究项目旨在开发一种将增材制造工艺应用于混凝土施工的新方法。研究的重点是创造一种基本的方法来建造自由形式的混凝土结构和适当的必要材料。所提出的制造工艺>选择性绑定是一种狭义的3D打印方法。通过局部引入可流动材料，将颗粒材料的薄层选择性地结合在一起，形成一层一层的固体，这种固体以前是用计算机设计的。将研究该方法的两种变体：a)在>湿式印刷中，采用细骨料层，并通过粘结剂膏的点引入选择性地结合。b)在>选择性活化<中，使用骨料和粘结剂粉末的混合物，通过引入水激活水化过程。迄今为止，研究人员只考虑了混凝土构件增材制造的挤压工艺。这种方法的显著缺点是限制了悬挑截面的生产，严重降低了几何设计的自由度。在一个已发表的关于生产建筑元素的选择性结合的项目中，波特兰水泥没有被用作结合剂。然而，由于其几何自由度，选择性绑定在建筑中具有最大的应用潜力。为了在混凝土强度、变形和耐久性方面积累丰富的混凝土技术经验，并确保必要材料的可用性，在拟议的研究项目中考虑了基于硅酸钙的粘合剂。此外，计划首次尝试使用3D打印技术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试验中得到证实。为了在高施工速度下应用选择性结合方法生产高分辨率、尺寸稳定、强度和耐久性的自由形态混凝土构件，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.