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只能使用传统的制造工艺来生产，这是非常困难的。增材制造工艺（3D打印）允许在几何形状的选择上有很大的自由度，这是一个有前途的替代方案。虽然这种方法现在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在少数研究项目中得到考虑。该研究项目旨在开发一种新方法，用于混凝土施工中的增材制造工艺。该研究的重点是创建一个基本的方法来构建自由形式的混凝土结构和适当的必要材料。拟议的制造过程>选择性结合<是一种狭义上的3D打印方法。通过局部引入可流动材料来选择性地结合颗粒材料的薄层，以逐层形成先前使用计算机设计的固体。将研究该方法的两种变体：a）在>湿法印刷<中，施加细骨料层，并通过点引入粘合剂浆料来选择性地粘合。B）In >选择性活化<应用骨料和粘结剂粉末的混合物，并通过引入水来活化水化过程。到目前为止，研究人员仅考虑挤出过程用于混凝土元件的增材制造。这种方法的显著缺点是，悬伸截面的生产受到限制，这严重降低了几何设计的自由度。在一个公开的关于选择性粘合用于生产建筑构件的项目中，波特兰水泥未被用作粘合剂。然而，由于其几何自由度，选择性结合在建筑中的应用潜力最大。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，还计划首次尝试使用3D打印技术生产钢筋混凝土构件。申请人进行的初步测试证明了所选方法的可行性。需要进一步的基础研究，以应用选择性结合的方法来生产具有高分辨率、尺寸稳定性、强度和耐久性的自由形式的混凝土元件，并且具有高的施工速度。

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.