# Jointing Principles in AMC--Part 1: Design and Preparation of Dry Joints
## 1 Introduction  
The modern world is changing faster than ever before, and the civil engineering field is no exception to that. Therefore, the requirements for the construction industry are increased speed, sustainability, and being digital to remain economical and become more efficient. With its long duration of planning, high carbon emissions, and questionable digitalisation, the construction industry faces formidable challenges to become less bureaucratic, more resource-efficient and intelligent. In that sense, new digital technologies like building information modelling (BIM) and 3D-concrete printing are gaining increased popularity. Three dimensional (3D) concrete printing, or additive manufacturing in construction (AMC), can take place on-site as well off-site [1, 2, 3, 4]. For on-site printing, in other words, printing at the construction site, the dimensions of the entire components are limited to the size of the 3D-concrete-printer according to the used method. In a recent work, [PERSON] et al. [5, 6] described some examples for different methods in the case of large-scale 3D printing systems. However, these large-scale 3D-printing systems have their limitations, not in the pure scale of the component, but in the environment. For example, engineering structures like bridges, silos, towers cannot be printed in one single piece because the surrounding area is not usable or available. Therefore, the components must be separated into smaller pieces and merged by using joints. Off-site printing, i.e., printing in a prefabrication plant, limits the dimensions of the components to ease the transportation. To deal with this limitation due to the size of the printed components, either it is possible to optimize the topology of a layout so that a building does not require large components or to divide bigger elements into smaller elements and reassemble them with joints on the construction site. The jointing of several components is required for off-site printing and on-site printing as well. This shows the relevance of the jointing in AMC. Conventional jointing principles are nowadays match-cast and grouted joints [7; 8]. Match casting means that one joint of a structural element serves as a formwork for the other half of the pair (side). In this case, a conventional formwork is still required to manufacture the joint of the original structural element. As match casting still requires formwork, the procedure might only be efficient for linear structural components. Furthermore, shrinkage of the joint profile might lead to inaccuracy of its geometry causing difficulties in fitting and load transfer/distribution [9]. On the other hand, grouted joints require even more attention in manufacturing because they do not only need formwork for the structural elements but also grouting for the joint. This sort of complicated and sometimes inaccurate manufacturing process could be listed as a disadvantage of this technique. In 2017, the first post-tensioned pedestrian bridge composed of extruded additive manufactured (AM) concrete segments and connected by grouted joints was built in the Netherlands. Compared to the conventional in-situ concrete construction method, time and cost savings were achieved regarding formwork, and the fabrication and installation of the reinforcement cages [10]. The manufacturing might have been more efficient if dry joints instead of grouted joints had connected the construction elements. In this case, the task of grouting the jointed elements could have been saved. One of the main advantages of the AM process (shoterete, extrusion, and particle-bed) is that the production of concrete segments is formwork-free. However, this advantage might disappear if the dry joint between the concrete segments itself requires formwork. \"Zero tolerance\" dry joints are manufacturable via match-cast [11], CNC-milled (CNC: Computerized Numerical Control) high-precision formworks [11; 12], high-pressure water jet cutting (WJC) [13] and CNC-concrete milling technology [14].