Extrusion-based 3D concrete printing (3DCP) is a promising technique for fabricating complex concrete elements without formwork, offering advantages like cost reduction and enhanced design flexibility by decoupling manufacturing costs from part complexity. However, this extended formal freedom is still constrained by the fabrication process and material properties. This paper presents a novel method for applying topology optimisation internally i.e. preserving the external boundaries of the concrete element while reducing material use and weight. This method adapts the extrusion thickness along the part according to the expected stresses, reducing the material use while enhancing structural performance. To validate this method, three different unreinforced 3DCP beams are tested in three-point bending. Results show that beams with optimised material distributions presented a higher strength-to-weight ratio, averaging 47% and 63% compared with the conventional 3D printed beam. This paper demonstrates the potential of internal topology optimisation for improving the efficiency and sustainability of 3DCP.

The transition from conventional cast concrete to 3D Concrete Printing (3DCP) marks a paradigm shift by directly depositing fresh concrete layer upon layer according to a digital model without the need for a formwork. This technology offers the possibility of achieving innovative and complex geometries in an automated process. Additionally, the implicit digitalisation introduced by this technology streamlines the interaction among different stakeholders, thereby reducing human errors and augmenting construction quality.

Nevertheless, despite its potential, methods for fully exploiting the design capabilities of 3DCP are still largely underdeveloped. This is primarily due to the assumed separation between the design process and the generation of manufacturing instructions. While the current driver for this technology is linked to increasing productivity and reducing labour costs, its most significant contribution may well be in the manufacturing of material-efficient structures by automatically integrating structural analysis into the designprocess.

This licentiate thesis aims to extend the design scope for this rapidly maturing technology by investigating its design possibilities, relevant printing parameters, and structural optimisation capabilities within the inherent restrictions of the process. The research focuses on the development of integrated design-to-manufacture workflows for the manipulation, analysis, and optimisation of print paths considering material and process constraints. Additionally, a comprehensive literature review is conducted, with a particular emphasis on the expansive design capabilities of 3DCP.

Experimental studies encompassed the design, manufacturing, and testing of concrete prototypes using a custom-made 3DCP system based on a robotic arm. The results demonstrated that customised material distributions can be successfully programmed and executed, resulting in prototypes with enhanced structural performance. Laboratory tests on topology-optimised unreinforced 3DCP beams revealed a substantial increase in load-bearing capacity per unit weight compared to conventional 3D printing patterns. The thesis aligns with the broader sustainability goals of the construction industry. Even though the cement content in 3D printed concrete currently tends to be higher compared to conventional methods, the potential of the technology for optimising material use, minimising waste, and incorporating additional functionalities to structures presents significant opportunitiesfor reducing the environmental footprint of concrete construction. By integrating manufacturing constraints into the design process, this study delineates a pathway for extending the design possibilities of 3DCP toward the implementation of material-efficient structures with graded properties. Ultimately, this study contributes to bridging the gap between digital design and digital fabrication methods, thereby advancing concrete construction practices.

Övergången från traditionell gjuten betong till 3D-betongutskrift 3D Concrete} Printing eller 3DCP) markerar ett paradigmskifte genom att direkt deponera färsk betong lager för lager enligt en digital modell, utan behov av formar.  Denna teknik erbjuder möjligheter att uppnå innovativa och komplexa geometrier genom en automatiserad process. Dessutom förenklar digitaliseringen interaktionen mellan olika intressenter, vilket minskar mänskliga fel och ökar byggkvaliteten.

Denna licentiatavhandling syftar till att utvidga designomfånget för denna snabbt växande teknik genom att undersöka dess designmöjligheter, relevanta utskriftsparametrar och kapaciteter för strukturell optimering inom de rådande begränsningarna av processen. Forskningen fokuserar på utvecklingen av integrerade design-till-tillverkning-flöden för styrning, analys och optimering av utskriftsvägar med hänsyn till material- och processbegränsningar. Dessutom genomförs en omfattande litteraturöversikt med särskild betoning på 3DCP:s expansiva designkapacitet.

Experimentella studier omfattade design, tillverkning och testning av betongprototyper med ett skräddarsytt 3DCP-system baserat på en robotarm. Resultaten visade att anpassade materialfördelningar framgångsrikt kan programmeras och genomföras, vilket resulterade i prototyper med förbättrad strukturell prestanda. Laboratorietester på topologioptimerade oarmerade 3DCP-balkar visade en betydande ökning av bärförmåga per enhetsvikt jämfört med konventionella 3D-utskriftsmönster.

Forskningen ligger i linje med byggbranschens övergripande hållbarhetsmål. Även om cementinnehållet i 3D-utskriven betong för närvarande tenderar att vara högre jämfört med konventionella metoder, erbjuder teknologin potential att optimera materialanvändning, minimera spill och lägga till funktionaliteter i konstruktioner, vilket ger möjligheter att minska betongkonstruktioners miljöavtryck. Genom att integrera tillverkningsbegränsningar i designprocessen skisserar denna studie en väg för att utöka designmöjligheterna för 3DCP mot implementering av material-effektiva konstruktioner med varierande egenskaper. Slutligen bidrar denna studie till att överbrygga klyftan mellan digital design och digitala tillverkningsmetoder, och därmed främja betongbyggandets metoder.

Tracking of building components can be instrumental in reuse for a Circular Economy. Tracking technologies (TT) for building components can be used to identify and access information for decision-making from deconstruction to design for reuse. Prior research has mainly been concerned with single technologies, limited life cycle applicability and new construction. This study aims to explore the potential of combining multiple technologies, such as QR codes, NFC, and Bluetooth tags, with BIM to support reuse along the life cycles of prefabricated concrete components. The benefits and limitations of choices in TT are examined concerning information integration in circular construction.

In recent years, there has been a growing interest in adopting circular approaches in the built environment, specifically reusing existing buildings or their components in new projects. To achieve this, drawings, laser scanning, photogrammetry and other techniques are used to capture data on buildings and their materials. Although previous studies have explored scan-to-BIM workflows, automation of 2D drawings to 3D models, and machine learning for identifying building components and materials, a significant gap remains in refining this data into the right level of information required for digital twins, to share information and for digital collaboration in designing for reuse. To address this gap, this paper proposes digital guidelines for reusing precast concrete based on the level of information need (LOIN) standard EN 17412-1:2020 and examines several CAD and BIM modelling strategies. These guidelines can be used to prepare digital templates that become digital twins of existing elements, develop information requirements for use cases, and facilitate data integration and sharing for a circular built environment.

While 3D concrete printing (3DCP) has surged in popularity, methods to harness its design potential remain largely underdeveloped. Existing design-to-manufacture workflows most commonly restrict the design to the overall geometry and a set of print parameters that may fall outside of the scope of the designer. This study presents a novel approach to integrate design and manufacturing by an integrated design-to-manufacture workflow that allows the gradation of the wall thickness along the printed part, which can be independently manipulated using established computer graphic techniques like texture projection and mesh coloring. The effectiveness of this workflow is demonstrated through the fabrication of a test body featuring a customized surface pattern. This approach aims to extend the design scope for 3DCP, enabling the addition and editing of surface patterns without geometry or code manipulation.

In concrete structures, material performance is typically determined at the level of the concrete mix (the microscale) and the overall shape and dimensions of a building element (the macroscale). However, recent developments in the field of 3D Concrete Printing (3DCP) are demonstrating that the design of concrete now also can take place at a previously impossible intermediate scale involving the shaping and placement of the material at the level of the printing nozzle (the mesoscale). By focusing directly on the design of print paths, advanced surface effects and internal porous material distributions can be achieved that significantly affect the aesthetic experience and structural performance of 3DCP structures. This ability to design the distribution of concrete according to local architectural, structural, and functional design criteria is an especially interesting application of 3DCP that could be exploited to customise material performance while at the same time optimising material use and reducing the self-weight of building elements. This paper specifically examines how four different three-dimensional print patterns produce distinct material structures at the mesoscale (mesostructures) and presents an experimental procedure for evaluating their load-bearing capacity.

Functionally graded materials (FGMs) describe composite materials with a gradual change in properties along one or several axes. A major advantage with this approach is the avoidance of discontinuities between different layers of material. 3D Printing offers the possibility to control the material composition and spatial placement along the printing process to create structures with graded properties. However, there are very few examples of the application of this approach to 3D concrete printing (3DCP). This paper presents a review of the current approaches of and methods to grade the material properties of a 3DCP structure, as well as a review of similar methods used in other 3D printing processes. Finally, the potential applicability of these principles into concrete are presented and discussed.

In concrete design, material performance is typically defined by the composition of the concrete mix (micro scale) and the overall shape and design of building elements (macro scale). However, recent developments in the field of 3D concrete printing (3DCP) are demonstrating that the design of concrete now also can take place at an intermediate scale involving the spatial organization of the material at the level of the printing nozzle. A growing body of work is showing how the additive process can result in novel material configurations through the programming of print paths. This paper specifically examines the relationship between the spatial organization of concrete at the mesoscale and its overall structural performance and presents an experimental procedure for evaluating the load bearing capacity of a selection of generated mesostructures.

Due to concrete’s traditional role as a casting material its appearance as a uniform solid mass is one of the material’s most distinct traits. When poured in a mould fresh concrete adheres to the shape of the formwork and material distribution is not adaptable at a more detailed level. This paper explores how deposition-based additive manufacturing opens up new opportunities for controlling the distribution of concrete at a previously neglected intermediate scale - the meso-scale. By adopting principles of knitting to toolpath planning, the paper presents a computational method for varying the density, porosity, and surface articulation of the material, previously inconceivable due to the limitations of formwork.