3D Concrete Printing (3DCP) enables the manufacturing of complex structures without increasing the costs of the process. However, this increased complexity is limited by conventional design workflows based on boundary representation 3D modelling and conventional slicing methods. While previous research has demonstrated the potential of print paths as a design method for customised structures and surface qualities, their use to generate controlled porosity in 3DCP structures is still unexplored. This paper investigates the use of print patterns at the scale of the printed filament to control the porosity, material distribution, and surface area of 3DPC structures, creating variable porosity and permeability that enhance design flexibility in 3DCP. For this, seven printing patterns were developed and tested to assess the relationship between exposed surface area and material use. The findings demonstrated that alternating patterns could create permeable structures with an extended surface area, which enables the creation of multi-functional structures. This research contributes to extending the design possibilities of 3DCP, allowing the generation of material properties that can be embedded and graded throughout the printed part.

The ReCreate project researches deconstruction and reuse of precast concrete elements, not originally designed for disassembly. Real-life deconstructions of precast concrete buildings in four countries (Finland, Sweden, the Netherlands and Germany), performed by ReCreate’s industrial partners as well as collaborators to harvest elements for reuse, were a key tool to gain experience and insights into deconstruction techniques and processes. The current report delivers an overview of what deconstruction entails. It gives best practice guidelines on the planning and implementation of deconstruction, as well as recommendations for improving the process.

While ReCreate’s country-specific deconstruction pilots themselves are described in a dedicated report (Vullings et al. 2024), they are also briefly summarised in the beginning of this report. The focus of the current report is, nevertheless, on turning the learnings from deconstruction pilots into generalisable guidelines that can be capitalised beyond the ReCreate project and the parties involved.

Deconstruction entails four main phases: pre-planning, structural deconstruction planning, deconstruction work planning, and finally, implementing the deconstruction. This report instructs on the different types of plans involved in each stage as well as their authors and contents.

Pre-planning involves pre-deconstruction auditing, i.e. inventorying reusable elements and gathering relevant information into an ‘inventory’ Building Information Model (BIM). The pre-deconstruction audit has been covered by another ReCreate deliverable (Vullings et al. 2022), which was delivered before ReCreate’s deconstruction pilots were fully complete. Therefore, the current deliverable briefly recaps the essentials of a BIM-based pre-deconstruction audit, and supplements and consolidates the findings of the previous report.

Authored by a qualified structural engineer, a structural deconstruction plan sets the foundations for a safe and efficient deconstruction process. It defines the deconstruction sequence based on structural stability; determines the need for temporary support and bracing measures; establishes cutting spots for connectors; gives a labelling scheme for logistics; instructs on correct lifting and transport of elements, as well as how to monitor the quality of elements on-site; and can help to define requirements for stripping.

A deconstruction work plan, devised by experts of the deconstruction company, translates the structural deconstruction plan into work processes: both the overall deconstruction process as well as element type specific processes. It covers aspects like workforce, equipment, work safety, site planning, and scheduling.

Finally, learnings acquired by implementing ReCreate’s deconstruction pilots are elaborated on. Findings are reported on deconstructing different types of elements; avoidable mistakes that were made which may influence the reusability (or at least the effort and cost of reuse) of the salvaged elements; the types of damage that is not easily preventable but an inherent part of deconstruction; and the influence of weather conditions on the deconstruction work. Additionally, special types of deconstruction projects are briefly discussed, such as partial deconstruction in the context of building remodelling, as well as combining deconstruction with conventional demolition.

While smaller, sub-process specific insights are scattered through the report, the main learnings of the key topics are distilled into checklists, given at the end of this report. The experience of the ReCreate deconstruction pilots shows that prerequisites for more widespread deconstruction already exist in that appropriately skilled workforce and suitable tools and equipment are widely available. The main technical and processual challenge in deconstruction is reconfiguring the existing know-how into safe and efficient deconstruction processes. This development can be further supported by small adjustments to existing tools that can help make the equipment even better suitable for deconstruction purposes. Nevertheless, it should be noted that a full evaluation of the success of ReCreate’s deconstruction pilots can only be made once the salvaged elements have been reused in new buildings.

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.

A process for ensuring the properties of deconstructed precast concrete elements is essential for safe reuse. The properties are important for structural designers when designing a new building with reused elements and evaluating their structural capacity and service-life.

The ReCreate project researches the process of reusing precast concrete elements through four real-life deconstruction and reuse pilots in Europe. The aim is to study different aspects of the whole process, including quality assurance.

To reuse precast concrete elements safely, it is essential to ensure their material properties. Especially when reusing load-bearing structures, certain properties, such as compressive strength, reinforcement details and cover depth of reinforcement, are required for evaluating structural capacity. However, the requirements for testing depend on the requirements of the new application, as the durability requirements may be different in different applications.

This document describes the tests done in each of ReCreate’s four real-life pilots in the different countries (Finland, Sweden, the Netherlands, and Germany).

The ReCreate project researches deconstruction and reuse of precast concrete elements, not originally designed for disassembly. ReCreate’s real-life pilots are a significant tool for achieving this goal. This report describes and illustrates ReCreate’s deconstruction pilots.

Six real-life deconstructions of precast concrete buildings – one in Finland, two in Sweden, one in the Netherlands, and two in Germany – are used in the ReCreate project to generate theoretical and practical knowledge about a wide range of topics directly related to the process of salvaging and reusing precast concrete elements. While the learnings regarding the planning and implementation of deconstruction are described in a centralised manner in another report (Vullings et al. 2024), the current report documents the donor buildings of the secondary elements as well as their practical deconstruction processes through textual descriptions and generous photographic illustrations and drawings. The donor buildings were blocks of flats (three buildings), public and private office buildings (two buildings) and industrial/warehouse buildings (one building). They had been deemed obsolete and were therefore slated for demolition. When engaged in ReCreate, they instead became vessels of knowledge generation for reuse-minded deconstruction. The various elements reclaimed from the donor buildings, such as sandwich panels, massive concrete slabs, massive interior wall elements, hollow core slabs, beams, and columns, will be reused in future in ReCreate’s reuse pilots. In addition to ReCreate’s six donor buildings, insights from following and observing two additional deconstructions, external to ReCreate, are also reported on herein.

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.

The traditional use of concrete in architecture is fundamentally conditioned by the inverse relationship that exists between material and formwork. When poured into a mold, a homogenous mixture takes the shape of its container. More detailed adjustment of the structure of concrete, however, is not possible. As a result, concrete appears to constitute a uniform soild mass; this is one of the material’s most distinct traits. In comparison, the process of shaping concrete by deposition signifies a fundamental departure from such conventional formwork-based techniques. Rather than relying on the constraint and control imposed by a rigid mold, deposition employs a computer-controlled machine to deposit material along a programmable path. The singular operation of the pour is thus replaced with a dynamic, choreographed flow, in which the role of the line shifts from representing the perimeter of the form to constituting the path along which the material performs.  

In addressing the main research question—How can concrete deposition lead to new ways of thinking and making architecture?—this thesis proposes that the shift from casting to programming concrete represents an opportunity for reevaluating values and conceptions that have shaped our understanding of concrete as a monolithic and uniform building material. In seeking to develop an alternative to traditional formwork-based construction methods, the research proposes that concrete deposition opens up new potentials for extending the resolution of design to encompass material distribution at a previously impossible, intermediate scale: the meso scale (10^-2–10^-1 m). Elaborating on this main research question, the thesis specifically asks how choreographing the flow and distribution of concrete at the scale of the deposited filament can lead to the production of intricate and porous material structures, something that was previously unfeasible due to the limitations of the mold. 

The thesis is divided in three main parts and consists of seven chapters. The first part (Beginnings) outlines the aims of the investigation and provides a background to the research questions. The initial chapters present an overview of the research field and the theoretical and methodological framework employed in the research. In the second part (Projects), the main research question is broken down and addressed in three projects related to the preparatory processes of mixing, testing, and stitching. The third part (Synthesis) presents a discussion and a conclusion. The Appendix contains a catalogue of stitches.

Denna avhandling undersöker betongens potential som byggnadsmaterial med en robotstyrd framställningsmetod där betongen appliceras och byggs upp i lager genom en additiv process. I syfte att bidra till att utöka de arkitektoniska möjligheterna med denna teknik så omprövas betongens etablerade roll som ett massivt och uniformt byggnadsmaterial. Inom forskningsprojektet har nya metoder utvecklats i syfte att utforska samverkan mellan betongens egenskaper och de robotstyrda rörelser som styr materialets placering. 

I en traditionell byggprocess måste en gjutform först tillverkas, fyllas med betong, och sedan demonteras för varje tillverkat betongelement. Betongblandningen antar formen av den konstruerade gjutformen och resulterar i en solid materialkropp med en sammansättning som inte kan anpassas på en mer detaljerad nivå. Att digitalt applicera betong genom additiv framställning innebär en väsentlig skillnad mot gjutformsbaserad tillverkning. Istället för att en statisk behållare ger form åt materialet så placeras betongen av en robotarm utefter en förprogrammerad linjebana. Gjutprocessen ersätts därmed av ett dynamiskt flöde där robotens koreograferade rörelser vägleder materialet.

Den övergripande frågan i avhandlingen är – hur kan additiv framställning av betong leda till nya sätt att tänka och bygga arkitektur? Mot denna bakgrund föreslås att skiftet från att gjuta till att koreografera betong utgör en möjlighet att omvärdera tankesätt och normer som hittills begränsat betongen till att vara ett massivt och uniformt byggnadsmaterial. Möjligheten att forma materialet i samma geometriska skala som munstyckets öppnar en ny dimension i utformningen av betong på en tidigare omöjlig mellanliggande skala – mesoskalan (10^-2 – 10^-1 m). Programmerbara rörelsemönster ger möjlighet att skapa lokala variationer i betongens uppbyggnad, variationer som i sin tur resulterar i intrikata och porösa materialstrukturer som tidigare varit omöjliga på grund av gjutformens begränsningar. 

Avhandlingen består av sju kapitel och är indelad i tre delar. Den första delens inledande kapitel presenterar de teorier och metoder som använts, samt beskriver de samarbeten och miljöer i vilka forskningsarbetet växt fram. Det andra kapitalet ger en allmän överblick av betongens historiska utveckling inom arkitektur och teknik och diskuterar olika förutsättningar för betongframställning med och utan gjutform. Mot denna bakgrund observeras hur byggnation med betong som regel gör en tydlig särskiljning mellan form och material. Inom additiv framställning kan samma tendens urskiljas genom att den fysiska gjutformen ersätts med en “virtuell gjutform” i form av en 3D-modell. Denna tendens att reducera material till en passiv mottagare av en aktiv form kan härledas till ett utpräglat hylomorfiskt tankesätt som är en sammanslagning av de grekiska orden för hyle (material) och morfe (form). Genom att anknyta till existerande hylomorfisk kritik introduceras problematiken och begränsningarna med detta tillvägagångsätt, vilket leder till frågan, vad kan ett icke hylomorfiskt tillvägagångsätt inom additiv tillverkning vara? Det tredje kapitlet introducerar begreppet “digital materialitet” och beskriver det forskningsfält som projektet bidrar till. 

I avhandlingens andra del undersöks de förberedande delmoment genom vilka den additiva processens potential realiseras. I tre kapitel med övergripande tema: blandning, provning och stickning behandlas beredningen av materialet samt programmeringen av robotens linjebanor genom att kombinera experimentella metoder med teoretiska resonemang och historiska reflektioner. Genomgående för de tre kapitlen är att de utgår från konceptuella verktyg och begrepp som utvecklats av filosofen Gilbert Simondon i hans kritik av det hylomorfiska synsättet. I fjärde kapitlet avhandlas inledningsvis hur betongen erhåller sina egenskaper och beteende i sitt tidiga stadium. Den förenklade förståelsen av betong som antingen flytande eller fast lyfts fram som otillräcklig och ersätts med en mer icke-binär förståelse av materialets komplexa transformationer. Kapitlets andra del beskriver en studie som innehåller den materialutveckling som varit nödvändig för forskningens praktiska arbete. 

I det femte kapitlet behandlas nya möjligheter för samspel mellan betong och design i tillverkningsprocessen. Utifrån ett resonemang om skillnaden mellan verktyg och maskin utvecklas ett argument om materialprovets viktiga roll inom maskinstyrda produktionsprocesser. Frågan som ställs är vilket samspel som kan existera mellan designintention, materialets beteende och roboten i den additiva processen. Mot denna bakgrund föreslås en provningsmetod där betongens följsamma och avvikande beteende kan studeras i relation till en specifikt utformad rörelsebana. 

I kapitel sex undersöks framställningen av robotens linjebanor. Inledningsvis diskuteras hur existerande metoder och programverktyg främjar ett hylomorfiskt tankesätt. I ett första steg i processen representeras solida kroppar i ett 3D-modelleringsprogram som ett yttre skal (makroskalan) utan möjlighet att ta hänsyn till materialets inre uppbyggnad på en mer detaljerad nivå (mesoskalan). När den framtagna 3D-modellen sedan anpassas för tillverkning sker det i en automatisk process som delar upp modellen i horisontella tvärsnitt. Detta delmoment är normalt utanför designerns räckvidd och reducerar den additiva byggnadsprocessen till staplandet av konturlinjer. Mot denna bakgrund utvecklas ett argument om behovet av att beakta linjebanorna som en del av designprocessen och att utformningen av linjerna i sig själva kan leda till hittills outforskade materialeffekter bortom den enkla lager-på-lager principen som blivit synonym med additiv framställning. Med inspiration från stickningstekniker utvecklar forskningsprojektet ett digitalt designverktyg som tillåter utökade valmöjligheter vid programmeringen av linjebanor till förmån för avancerade rörelsemönster. De framtagna linjerna kan liknas vid olika stygn som appliceras inom stickning av textilier. Inom ramen för projektet kallas de därför för “stitches”. Med detta tillvägagångsätt kan den additiva processen frambringa komplexa materialstrukturer inom materialets mesoskala, strukturer som ligger utom räckhåll för konventionella modelleringsmetoder. 

Avhandlingens tredje del innehåller diskussion och slutsatser som avslutas med en plan för vidare forskning. Avhandlingen innehåller också en katalog med genererade linjetyper.