Additive manufacturing with concrete can revolutionize the construction industry. The technology can contribute to the digitalization and automation of construction processes, leading to more efficient and cost-effective construction practices. Furthermore, it enables a radical rethinking of architectural design. Nevertheless, the implementation of this novel production strategy is accompanied by a series of challenges. Integrating reinforcement into the printed structure is one of the challenges to be addressed. An innovative solution is the robotic and dynamic winding of fibre reinforcement strands. New possibilities for reinforcing additively manufactured structures are opened up by this new type of reinforcement integration. To fully utilise these possibilities, three distinct integration strategies for wound reinforcement strands have been developed, namely Core Winding, Frame Winding and Pin-grid Winding. Previous research has shown the feasibility and benefits of integrating wound fibre reinforcement strands into 3D concrete printing in various smaller and larger experiments and demonstrators (including the Shelltonics demonstrator and the Knitcrete bridge), paving the way for more robust and versatile construction methods. The objective of this paper is to evaluate and compare the aforementioned processes in terms of their functional capabilities. Each process is analysed and classified according to its usability and limitations. This classification should support the determination of the most appropriate process for a particular application. The established framework allows the benefits of winding fibre reinforcement strands to be fully exploited, depending on the application.

As one of the most important sectors of the global economy, the construction industry has continuously sought to optimize its processes. However, construction remains characterized by a highly fragmented value chain, low productivity, and limited digitalisation. Introducing Cyber-Physical Construction Systems offers a way to address these challenges by enabling a more flexible, automated, and collaborative approach. In this paper, a cyber-physical design-to-fabrication workflow was developed using terrestrial laser scanning as a sensing tool, augmented reality as a design interface, and an extrusion concrete printer as an actuator. As a result of the cyber-physical construction workflow, two benches were digitally fabricated as a case study by combining reclaimed bricks with 3D concrete-printed components. The developed workflow enables designers to use augmented reality to generate an adapted path for 3D-printed structures. The study highlights the potential of Cyber-Physical Construction Systems to improve automation and efficiency while fostering human-robot collaboration through human-in-the-loop approaches. However, the case study revealed key challenges, including gaps in automation and scalability, that must be addressed for broader implementation. Future work should focus on refining the integration of sensing technologies, improving communication between digital and physical systems, and optimizing collaborative workflows to leverage the benefits of Cyber-Physical Construction Systems in construction fully.

This study introduces a digital fabrication process for producing recyclable, closed-loop wax formwork for architectural concrete applications with visually rich surface articulation while drastically reducing formwork milling time. As such, this paper presents (a) a circular large-scale production method for wax blocks via a single casting process; (b) four machine-time-optimized surface articulation strategies through CNC toolpath-driven design; (c) the investigation of different coating systems to improve architectural concrete surface quality and to ease demolding; and (d) the integration of robotic concrete shotcreting using a low-CO2 fine-grain concrete. For the first time, wax formwork technology, characterized by its waste-free approach, has been combined with robotic shotcreting in a digital and automated workflow to fabricate fiber-reinforced, geometrically complex thin-shell concrete elements with distinct surface articulations. To evaluate the process, a series of four thin-shell concrete elements was produced, employing four distinct parametric toolpath-driven designs: linear surface articulation, crossed surface articulation, topology-adapted curve flow surface articulation, and robotic drill topology-adapted surface articulation. Results revealed a possible reduction in milling time of between 77% and 94% compared to traditional milling methods. The optimized toolpaths and design-driven milling strategies achieved a high degree of visual richness, showcasing the potential of this integrated approach for the production of high-quality architectural concrete elements.

This manuscript presents the development of Discrete Selective Robotic Rammed Earth, a novel robotic fabrication method that advances the use of earthen and regenerative materials in automated construction. This work aims to promote more sustainable construction practices and to respond to the urgent need for climate action within the architecture, engineering, and construction industries. The presented technique advances the integration of automation into earthen construction by adapting the standardized rammed-earth method into a robotic fabrication process that eliminates the need for conventional formwork and deploys robots for the labor-intensive materialization process. Our technique combines the strengths of selective particle-bed additive manufacturing techniques with those of the well-established rammed-earth construction system. The approach relies on a discrete design method that organizes material and geometry into controllable volumetric units. This discrete design-to-fabrication method is tailored to the capacities and constraints of rammed earth. This work demonstrates how robotic fabrication can replace the conventional formwork in rammed-earth construction while overcoming its geometric limitations by shifting the complexity from geometry to the process of digital materialization.

In this paper, Injection 3D Concrete Printing (I3DCP), a novel 3D concrete printing technology, is presented. I3DCP comprises - in the presented "Concrete in Suspension" variant - the injection of concrete into a non-hardening carrier liquid (limestone powder suspension). In contrast to "conventional" 3D concrete printing, I3DCP enables the fabrication of lightweight and modular components through printing spatially free trajectories. Within this paper, the current status of research in terms of structural design, modularization, material-process interaction and reinforcement integration of this technology is presented. Selected results on the effect of rheology on the quality of nodes and on the relevance when encasing reinforcement are presented and discussed.

Injection 3D Concrete Printing (I3DCP), where material is robotically injected into a carrier liquid and remains stable has been successful at producing complex concrete structures. I3DCP is capable of overcoming the directional limitations faced by other additive fabrication methods. However, this technology has been limited to producing compression-only structures, as its thin concrete strands are incapable of withstanding significant tensile loads. A potential solution is the introduction of reinforcement into concrete structures. This study focuses on the injection of a fine grain concrete into a carrier liquid with defined rheological properties and the capability to encase reinforcement bars, which are spatially fixed inside the carrier liquid, during the printing process. The effect of material- und process related parameters on the encasement quality are studied. The rheological parameters of the carrier liquid are varied by solid volume fraction and the addition of viscosity modifying admixtures. The shape of the nozzle (flat/U-Shape), the nozzle traverse speed (ranging from 20 mm/s to 60 mm/s) and the distance from nozzle to rebar (ranging from 5 mm to 15 mm) are systematically studied. The quality of the encasement is evaluated by image analysis. Selected probes are mechanically tested in pull-out-tests. It is observed that with increasing yield stress of the carrier liquid the reinforcement is less encapsulated. This effect can be counteracted by changing the nozzle shape and/or print speed. Finally, the potential and limitations of using reinforcement bars in I3DCP are discussed.

The Digital Fabrication with Concrete (DFC) enables freedom of form. In order to fully leverage this freedom, the reinforcement should be rethought, as well. Such an opportunity is provided by the Robotic Fibre Winding (RFW). This in-situ and on-demand produced fibre reinforced polymer reinforcement can provide endless strands, which can be either digitally deposited on concrete (concrete defines the form) or on a frame with subsequent application of concrete (reinforcement defines the form), and combined particularly successful with the digital shotcrete or Shotcrete 3D Printing (SC3DP). The current paper critically analyses the results of the three previously published experimental campaigns with glass fibre wound reinforcement: 1) one set of pull-out and direct tensile tests with various RFW reinforcement types embedded in cast concrete, and 2) two sets of four-point bending tests with two different RFW reinforcement types. In all cases the experimental results are re-analysed from the structural engineering point of view, with the special consideration of anchorage length required for the full activation of reinforcement. On basis of the obtained results it is concluded, that despite theoretically good bond, resulting in required anchorage comparable to this of classical steel bars, many bending tests unexpectedly ended in pull-out failure. Hence, the mode of pull-out failure should be carefully observed in the upcoming experiments. Likewise, the focus should be put in the future on collection of all relevant data required for such detailed investigation of the bonding zone.

Injection 3D Concrete Printing (I3DCP) is an emerging fabrication technique that enables spatial concrete extrusion within a carrier liquid, reducing gravitational effects and allowing the creation of complex space trusses. However, I3DCP introduces new challenges in toolpath planning due to material rheology and mechanical constraints. This paper introduces an automated planning method tailored for I3DCP, integrating a constraint satisfaction problem (CSP)-based sequence planner with a Cartesian motion planner. The sequence planner uses heuristic local search with forward checking and backtracking, while the motion planner addresses end-effector redundancy with kinematic and velocity constraints. The method is validated by fabricating a 3-meter-span pedestrian bridge using a stationary 6-axis robotic arm and tested on multiple prototypes of increasing geometric complexity through simulation, demonstrating its effectiveness and scalability for intricate structural designs.

This paper presents a form-finding approach for Injection 3D Concrete Printing (I3DCP) using Vector-based Graphic Statics (VGS). This approach adopts a top-down strategy, initiating a preliminary global design in the form of a space truss and integrating structural and fabrication constraints specific to I3DCP. A form-dependent self-weight load is applied throughout the form-finding process until the structure achieves static equilibrium. As the current I3DCP setup is mounted on a robotic arm with a stationary base, the feasibility of the designed structure for I3DCP is assessed, ensuring compatibility with the robotic arm's workspace. Structures exceeding the workspace boundaries are segmented and individually optimised, subject to topological and geometrical constraints. The optimised segments are then merged into a single assembly to complete the process. This approach is demonstrated through the design and construction of a 3-metre-span pedestrian bridge. This prototype is 3D scanned and then analysed via the finite element method to evaluate its mechanical performance.

The integration of reinforcement in digital fabrication with concrete has led to the development of various approaches, many of which are constrained by the requirements of the concrete printing process. In contrast, the aim here was to investigate the robotic production of complex reinforcement structures as a primary process which supports the application of concrete and therefore acts as stay-in-place formwork that creates shaping potential beyond conventional printing processes. Based on the concept of combining the robotic processes of Fibre Winding and Shotcrete 3D Printing (SC3DP), the presented methodology comprised design explorations, fabrication variations, the realisation of a real-scale demonstrator and the assessment of the structural performance. Accordingly, an automated process for the fabrication of thin-shell double-curved reinforced concrete elements with controlled thickness and homogeneous concrete distribution was developed and characterised. Following this approach in the future will not only contribute to fabrication-informed design but also minimise concrete use and formwork waste.

The construction industry is facing a dual challenge: an increasing demand for new buildings on the one hand and the urgent need to drastically reduce emissions and waste on the other. One promising field of research to face these challenges comprises additive manufacturing (AM) technologies. Through these advanced methods, digital workflows between design and fabrication can be implemented to optimise the form and structure, unlocking new architectural freedom while ensuring sustainability and efficiency. However, to drive this transformation in construction, the new technologies must be investigated in large-scale applications. One of these fast-emerging AM techniques is Shotcrete 3D Printing (SC3DP). The present research documents the 1:1 scale manufacturing process, from digital to real, of a building section utilising SC3DP. A workflow and production steps, spanning from design over manufacturing to assembly, are introduced. The architectural design, reinforced by computational methods, was iteratively refined to adapt to manufacturing constraints. The paper also emphasises the importance of a digital twin in ensuring seamless data integration and real-time adjustments during construction. By incorporating reinforcement techniques such as short rebar insertion and robotic fibre winding, this study demonstrates the structural capabilities achievable with SC3DP. In summary, the implementation of comprehensive digital workflows utilising computational design, automated data acquisition and data flow, as well as robotic fabrication is presented to demonstrate the potential of AM methods in construction. Furthermore, this paper provides a perspective on potential future research paths and opportunities inherent in leveraging the innovative SC3DP technique.

Digital fabrication is the design and manufacturing workflow allowing for computer-guided additive and subtractive manufacturing. In construction, it opens up new possibilities for efficient and reduced use of materials, thanks to tailored design and bespoke serial production of structural elements. The Institute of Structural Design (ITE) for around a decade researches tools and strategies of additive and subtractive fabrication, with a particular focus on the process-material compatibility. These methods allow for placing a material of desired characteristics exactly where required to optimise form and properties, minimising material consumption and hence reducing the footprint of a structure. This paper discusses various fabrication strategies developed by ITE and its partners in interdisciplinary research, with a special focus on the potential towards bringing sustainability into architecture and construction sector. The discussed methods encompass Shotcrete 3D Printing, Robotic Rammed Earth, Large Particle 3D Concrete Printing, recyclable wax formwork, subtractive and additive manufacturing for the reuse and recycling of concrete, and Hybrid Wire-and-Arc Additive Manufacturing (WAAM) I-beams. Each method is briefly introduced, and its potential impacts on sustainability are discussed.

Architects and engineers have historically developed and reinvented concrete's technologies, formwork and aesthetics to suit the pragmatic and philosophical aims of their times. Architect and computational design researcher Norman Hack and his co-authors introduce a contemporary method for the fabrication of concrete structural elements using the Injection 3D Concrete Printing (I3DCP) process formulated at TU Braunschweig and discuss its benefits over other types of printed concrete.

Digital fabrication technologies, such as 3D concrete printing, are currently making their way into the construction industry. The primary focus in this field is often on the depositing processes, such as extrusion 3D concrete printing, where material is typically applied in horizontal planar layers. This area has seen substantial progress in recent years. However, numerous research and development projects are specifically targeting the additive manufacturing of unreinforced raw concrete components. When implementing these technologies in practice, it has become clear that additional processes, such as fully automated process-parallel reinforcement integration, application of cover layers and formative and subtractive post-processing of the components, are essential for successful application. In addition, by varying the orientation, characteristics and arrangement of the layers, new shapes and functions can be realised. Examples include angled layer orientation for producing vaulted geometries without support structures, as well as non-planar layer formation for complex component geometries or assembly joints. Moreover, alternative innovative manufacturing processes, such as KnitCrete, Smart Dynamic Casting or Injection 3D Printing, reveal new potential for the application of digital manufacturing technologies in the construction industry. This article aims to demonstrate the possibilities offered by digital fabrication with concrete beyond the stacking of horizontal planar layers, and how these technologies can complement and expand a future digital fabrication strategy in the construction industry.

Material, manufacturing process, and form are mutually dependent. In formwork-based concrete construction, the reinforcement must be positioned and fixed in the formwork, limiting material efficiency and freedom of form. In Digital Fabrication with Concrete (DFC), the formwork no longer limits the concrete forming process. Furthermore, the reinforcement no longer must be installed in advance, but can be placed before, during or after the concrete application. Therefore, the role of reinforcement and its interaction with processing must be fundamentally rethought in DFC. Furthermore, with reinforcement integration a concrete component expands from a contour-based shape into a structural form.The current paper proposes a new so-called RPF-framework expressing the interaction of reinforcement, process and form in DFC. The application of this framework is illustrated using current examples of DFC, whose structural forms are critically discussed. Finally, the need for a holistic approach to material, process and form in DFC is emphasised.

3D Concrete printing requires much more elaborate quality control procedures compared to conventional concrete processing. Due to the various process steps, and the corresponding variation in material behaviour, time-, and length-scales, a single quality indicator and measurement technique (similar to the ‘slump test’ for traditional construction) cannot be selected. Instead, three families of quality indicators have been established: homogeneity during material production and deposition (quality variations), material evolution during printing (transient material behaviour), and macroscopic features and geometric conformity during printing and of the final object (geometry). For each family, quality assessment techniques which have been proven in other fields or for different applications, have been successfully transferred and adapted to the 3DCP process. In some cases, completely new methods have been developed. This paper aims to provide the state-of-the-art in such quality assessment methods, indicating high potential methods and research gaps across all scale levels of 3D concrete printing processes.

There is the need to improve the ecological footprint of modern construction; accordingly, earth as a sustainable building material is increasingly coming into focus. Besides the material itself, digital fabrication of earth-based materials offers additional ecological potential, as it is possible to create individualized components without using formwork and at the same time save resources due to a form-follows-force approach. However, the material must be adjusted for being suitable for additive manufacturing, i.e. material needs to be pumpable, extrudable and subsequently buildable. In this paper, a workflow is presented that shows the possibilities for engineering an earth-based mixture. Therefore, a systematic characterization of mixtures is carried out. For this purpose, loam to water ratio and volumetric aggregate content are systematically varied and the addition of natural fibers is investigated. For the evaluation of pumpability and buildability, the yield stress is evaluated. Mechanical strength as well as drying shrinkage are assessed as solid properties for these earth-based mixtures. The results are discussed and the developed workflow is prototypically demonstrated by the successful fabrication of a demonstrator. Therefore, six stackable 3D printed elements are fabricated with extrusion and then assembled in a 2 m high column.

Through the deployment of a mobile construction robot capable of conducting high-resolution object scanning and precise in situ Additive Manufacturing (AM), we present a novel design-to-fabrication workflow for repairing existing building structures. The integration of AM techniques into context-aware mobile robotic systems enables high-precision in-place fabrication for new construction and for repair of existing structures. The benefits of transferring AM processes on-site extend in relation to tolerance handling, direct manipulation of existing structures, and removing constraints on shape stability compared to prefabricated elements by utilizing the context. By incorporating geometrical data obtained through 3D capture methods into the design and planning environment of architects and engineers, a direct interface between the existing building site and the planned digital geometry is created, facilitating accurate design of in-place repair or additions to existing building components. To evaluate this approach, we conducted an experiment in which a mobile robot equipped with a clay extrusion 3D printing system conceptually repaired a set of damaged brick wall segments. This workflow involved capturing the existing context with two levels of resolution: low-resolution 3D scene capture with a depth camera to generate a trajectory for high-resolution scanning, from which a dense point cloud is recorded using a 2D laser profile sensor by following the designated trajectories. This dense point cloud enables the operator to identify both the geometry of the existing brick wall, generate the missing volume, and a print path trajectory that fits the bounds of the volume while considering functional and architectural parameters. The accurate completion of the missing volume was successfully demonstrated by in-place 3D printing using clay extrusion with the mobile robotic system, showing the conceptual effectiveness of the proposed approach.

This paper describes a novel digital earthen fabrication concept referred to as Sprayed Earth Additive Manufacturing (SEAM), where earthen material is sprayed robotically with pressure in order to create a three-dimensional structure.Compared to processes based on material-extrusion, the adhesion between the sprayed layers is improved, the addition of material is controlled, and spatial flexibility is enhanced.Additionally, the possibility of adding natural fibers to the sprayed earthen mix allows enhancing the strength and the shrinkage behavior of the earthen material.The paper starts by addressing the current state of the art on reinforcement of earthen material, optimization of the spraying technique and automation in the construction process.It then demonstrates the applied methodology, early material research, explored spraying parameters such as the influence of air volume flow, nozzle velocity and nozzle to strand distance on the layer geometry and the implemented robotic fabrication setup for integrated fiber reinforced spraying.A novel concept of fiber integration, where a continuous fiber strand is chopped and added to the sprayed earthen material directly at the nozzle, was tested for the first time.Finally, the paper presents a series of the latest experimental results, reflections on the overall material reinforcement investigations and concludes with potential future explorations needed for the research.