Im Projekt Pareus Resort Caorle wurde das partikelbettbasierte Selective-Paste-Intrusion (SPI)-Verfahren erstmals gro ss ma ss st & auml;blich in der Fertigteilproduktion eingesetzt. Vor dem Hintergrund praxisrelevanter Expositionsklassen (XC4, XS1, XF2) untersucht der Beitrag das mechanische und dauerhaftigkeitsrelevante Verhalten additiv gefertigter SPI-Bauteile unter besonderer Ber & uuml;cksichtigung schichtbedingter Gef & uuml;gemerkmale. Die Ergebnisse zeigen, dass die volumetrische Frostresistenz ma ss geblich durch klassische betontechnologische Parameter, insbesondere den Wasserzementwert, bestimmt wird. Eine ausgepr & auml;gte Richtungsabh & auml;ngigkeit des relativen dynamischen Elastizit & auml;tsmoduls ist nicht feststellbar. Demgegen & uuml;ber weisen transportgesteuerte Mechanismen eine erh & ouml;hte Sensitivit & auml;t gegen & uuml;ber der schichtweisen Gef & uuml;geausbildung auf. Insbesondere bei der Karbonatisierung treten lokal stark erh & ouml;hte Tiefen entlang interlaminarer & Uuml;bergangszonen auf, die durch Mittelwertbetrachtungen nicht vollst & auml;ndig erfasst werden. Erg & auml;nzende CDF-Versuche verdeutlichen die Bedeutung randzonennaher Transportprozesse. Auf Grundlage mechanischer, dauerhaftigkeitsrelevanter und mikroskopischer Befunde wird ein zweistufiges Gef & uuml;gemodell vorgeschlagen. Die Dauerhaftigkeit additiv gefertigter SPI-Bauteile ergibt sich demnach aus dem Zusammenwirken materialtechnologisch gesteuerter Zementsteinporosit & auml;t und prozessbedingt ver & auml;nderter Porenkonnektivit & auml;t entlang der Schichtgrenzen. Durability of SPI elements - Influence of layer-induced structural featuresWithin the Pareus Resort project in Caorle, the particle bed-based Selective Paste Intrusion (SPI) process was implemented at industrial scale for the first time in precast production. Considering relevant exposure classes (XC4, XS1, XF2), this study investigates the mechanical performance and durability-related behaviour of additively manufactured SPI elements, with particular emphasis on layer-induced structural features. The results indicate that volumetric freeze-thaw resistance is primarily governed by classical concrete technological parameters, especially the water-cement ratio. No pronounced directional dependency of the relative dynamic modulus of elasticity was observed. In contrast, transport-driven mechanisms exhibit increased sensitivity to the layerwise structure. Carbonation tests reveal locally increased penetration depths along interlaminar transition zones, which are not fully captured by mean value evaluation. Complementary CDF testing highlights the relevance of surface-near transport processes under de-icing salt exposure. Based on mechanical testing, durability assessment and microstructural observations, a two-level structural model is proposed. The durability of SPI components results from the interaction between material-controlled cement paste porosity and process-induced variations in pore connectivity along layer interfaces.

To show compliance to structural engineering codes and implement quality control measures, it is critical to obtain reliable mechanical properties of the materials in question. For conventional cast and precast concrete, the experimental procedures and relationships between mechanical properties, the material composition, and the production methods are globally known, but for 3D concrete printing (3DCP), these relations have not yet been established. Previous studies have shown little consistency in results, and the underlying experimental methods have not been established broadly. There is an urgent need to address these issues as the application of 3DCP in practice projects is growing rapidly. Therefore, RILEM TC 304-ADC: Assessment of Additively Manufactured Concrete Materials and Structures has set up a large interlaboratory study into the mechanical properties of 3D printed concrete. This paper presents key elements of the experimental approach detailed in the Study Plan and the supporting considerations. Furthermore, it reports on the response, consisting of 34 contributions from 30 laboratories, detailing global coverage, properties of the applied mixture designs and characteristics of the printing facilities that have been used. Subsequently, some fundamental results from compression, flexural, and E-modulus testing are presented and—considering cast specimens as a reference—discussed. On average, a reduction in strength was found in compression and E-modulus (all tested orientations). For flexure, on the other hand, an increase was found in two testing orientations, while a decrease was observed in the third orientation. Importantly, even though the applied experimental methods were found to be reasonably appropriate to obtain the required data, the differences found between individual contributions are significant and sometimes non-consistent, suggesting that testing on specific material-facility combinations is necessary to reliably determine the mechanical properties of objects produced from them. Furthermore, a theoretical framework needs to be developed to further explain the variations that were observed. Extensive analyses of all acquired data are out of the scope of this contribution, but presented in two associated papers, whereas a third presents the data management approach used to process the approximately 5,000 test results.

Dieser Leitfaden, erstellt von der Arbeitsgruppe ,,Digitaler Betonbau durch additive Fertigung" des Deutschen Ausschusses fur Stahlbetonbau (DAfStb), dient als umfassende Ressource zur Unterstutzung von Planung und Durchfuhrung additiver Fertigungsprojekte im Betonbau in Deutschland. Er richtet sich an Architekten, Planer, Antragsteller, Materialhersteller, Bauunternehmen und weitere am Bau Beteiligte. Nach einer kurzen Vorstellung der Klassifizierung, Terminologie und Methoden der additiven Fertigung werden rechtliche Aspekte und Genehmigungsverfahren beleuchtet, um eine nahtlose Integration dieser Technologie in die Baupraxis zu gewahrleisten. Der Leitfaden behandelt die Einordnung additiver Fertigungsmethoden mit Beton in das Bauordnungsrecht, erlautert den Ablauf von Genehmigungsverfahren und bietet Orientierungshilfen zur Abstimmung von Zustandigkeiten bei Projekten. Er geht auf technische Regeln fur die Bemessung und Konstruktion von Tragwerken ein, insbesondere bei additiv hergestellten Wanden, und behandelt konstruktive Aspekte der Bewehrung. Ein wichtiger Bestandteil sind Beton- und Bauteilprufungen, einschliesslich der Methoden zur Probenherstellung sowie Prufverfahren fur Frisch- und Festbeton, was den Leitfaden zu einem hilfreichen Werkzeug fur Fachleute im Bereich des digitalen Betonbaus macht. Additive manufacturing with concrete - guidance for planning and implementation of projectsThis guideline, created by the DAfStb Working Group "Digital Concrete Construction through Additive Manufacturing," serves as a comprehensive resource to support the planning and implementation of additive manufacturing projects in concrete construction. It is intended for architects, planners, applicants, material manufacturers, construction companies, and other parties involved in construction. After a brief introduction to the classification, terminology, and methods of additive manufacturing, legal aspects and approval procedures are highlighted to ensure seamless integration of this technology into construction practice. The guide addresses the integration of additive manufacturing methods with concrete into construction law, explains the approval process, and offers assistance for coordinating responsibilities in projects. It addresses technical rules for the design and construction of structures, particularly for walls produced by additive manufacturing, and covers constructive aspects of reinforcement. An important component is concrete and component testing, including methods for sample preparation and testing procedures for fresh and hardened concrete, making the guide a useful tool for professionals in the field of digital concrete construction.

The Selective Paste Intrusion (SPI) is an additive manufacturing method in which aggregates in a particle bed are selectively bonded layer-by-layer with cement paste to build complex, free-formed concrete elements. To ensure both sufficient layer bonding and shape accuracy, the adjusted paste yield stress ( τ_0 ) needs to be almost constant during the entire printing period. The τ_0 depends beside others on the ambient air temperature. Temperature changes, as common in the precast plants, are transferred to the raw materials, mixing tools and printer peripherals. Thus, the fresh cement paste will vary in temperature. A change especially during the production process can either lead to insufficient layer bonding and thus strength of the built component or excessive spreading of the cement paste in the particle bed and thus poor shape accuracy. We therefore investigate the stability of the paste τ_0 at temperatures between 16 ℃ and 26 ℃ in steps of 2 ℃ each, starting at 20 ℃, which is the reference temperature. We found a continuously increasing τ_0 for increasing temperatures. This worsens the printing process i.e. the penetration depth of the paste, shown in simulations based on Darcy’s law. To ensure consistent component quality at varying ambient temperatures, the worsened penetration depth needs to be compensated by adjustments in either the mixture composition or the process parameters, e.g. velocity of the print head.

In this paper, the flow of concrete in a reinforced bored pile is analysed using computational simulations. In order to reduce the computational time, a porous medium that equally mimics the presence of the reinforcement is used. Experimental measurements are used as bounds on the material parameters describing the flow of fresh concrete. The influence of rheological properties of fresh concrete and the thickness of the porous medium that represents the reinforcements is analysed with a classical U-box simulation. Finally, casting of a bored pile is analysed using computational simulation implementing a porous medium representing the reinforcement cage. The concrete flow behavior and especially the filling of the concrete cover zone is analyzed for casting scenarios with different concretes varying in their rheological behavior. Simulations using the porous medium approach is 10x faster than simulations that explicitly model the reinforcements. Simulation results show that a good workability (low viscosity and low yield stress) of the initial batches of concrete must be maintained throughout pouring to avoid the risk of defect formation in the cover zone.

This book presents the work of the RILEM Technical Committee 276-DFC: Digital fabrication with cement-based materials.

The Selective Paste Intrusion (SPI) is an additive manufacturing method in which thin layers of aggregates are bond selectively by cement paste only where the structure shall arise. In this way, concrete elements with complex geometries and structures can be produced. To meet the optimum between required layer bonding and sufficient shape accuracy, the rheological properties of the cement paste, i.e., its yield stress and dynamic viscosity, are crucial [1, 2]. The combination of the SPI process and the Wire and Arc Additive Manufacturing (WAAM) process enables the production of free-formed, high-strength reinforced concrete elements, which opens up a wide range of applications. However, the WAAM process generates high temperatures, which affect the rheological properties of the cement paste and thus the printing quality [3, 4]. Therefore, we analyzed the effect of external temperature loads on the rheological performance of cement paste over the entire SPI production period and derived a maximum acceptable temperature load for the combination of SPI and WAAM. The experiments showed decreasing viscosity and increasing yield stress values by stepwise increasing the paste temperature from 20 °C to 60 °C. Between 60 °C and 70 °C, the rheological behavior suddenly changed, and both viscosity and yield stress instantly increased to a multiple of their initial values. In a subsequent numerical simulation of the intrusion behavior of the paste in the particle bed, we could show that the high yield stress and viscosity lead to poor paste penetration and thus insufficient layer bonding, whereas paste temperatures up to 60 °C are not detrimental to the SPI process. Therefore, the results demonstrate that the combination of SPI and WAAM is possible if the WAAM process is adjusted by e.g. cooling strategies, increased distance of the welding point from the particle bed, or increased time intervals between the welding points to avoid paste temperatures exceeding 60 °C.

After only a few of years of intensive research all over the world, 3D printing of buildings has been induced in practical application in construction industry. In the course of this, in 2021, the first 3D printed residential building was realised in Beckum, Germany. The aim of this paper is to give an insight to the impetus, the ideas and the individual steps to realize this project. We describe the technology used and give an overview about background of the material development and the requirements for the material. Furthermore the architectural design und planning process is displayed. However, existing design codes do not cover all special technical features of the new construction method. Consequently, we describe the concept how the building permission (approval) for the construction by following existing standards (DIN EN) for concrete and masonry construction was achieved and granted. Finally we give an insight in the construction process and conclude with lessons learned for future projects.

3D printing is offering a totally new construction method, but an in-depth understanding of the consequences of the different production conditions compared to traditional formwork-based casting operations is required. Bulk material properties (intrinsic strength and durability) will follow the same fundamental material laws. However, in printed structures, the role of the interfaces will become increasingly important as they affect the mechanical performance, transport properties and durability behaviour. Additionally, the anisotropic nature of 3D printed structures implies that there are new opportunities to develop new methods of analysis. The aim of this chapter is to focus on the current practices for performance testing and to give an overview of the parameters which affect the hardened properties of a printed cementitious material.

This paper focuses on material-process interactions in particle bed binding. After a classification of particle bed binding techniques currently available for cement-based materials, the most important material-process interactions and their underlying physics are discussed in detail for the selective cement activation (SCA) and the selective paste intrusion technique (SPI). Here, we consider the sub-processes layer application, layer compaction, fluid application, fluid penetration and after printing treatment. We show that, by varying the material and process parameters in these sub-processes, the printing process and the resulting material properties of the printed component, such as compressive strength, durability and dimensional accuracy, can be specifically controlled. Furthermore, we illustrate how these sub-processes can be both understood and described on the basis of the underlying mechanisms and physically based material models.

For the selective paste intrusion (SPI) method, thin layers of aggregate are locally bound by cement paste where the structure shall arise. After completion of the printing process, the structure is excavated from the particle-bed and the unbound particles are removed. However, for a sufficient layer bonding and shape accuracy, the rheology of the cement paste must be adapted to the flow resistance of the particle-bed. For practical application, that means mostly time and material consuming “trial and error” tests. To prevent that, analytical models can help to predict the penetration of the cement paste. This paper presents four analytical models to calculate the penetration depth of a cement paste into a particle packing. Based on Darcy’s law, an already existing model is slightly modified (model A+) and a generalized (model C), an advanced generalized (model D) as well as a simplified model (model B/B+) are developed. Compared to conducted tests on the penetration depth, model B showed good accuracy (deviation <1.5 mm) for pastes with a yield stress ≥8.2 Pa, model A+/B+/C for ≥ 5.4 Pa and model D even for <5.4 Pa. Finally, an application guide for each model for practical use will be given.

Die digitale Fertigung mit Beton (DFB) ist ein sich überaus dynamisch entwickelndes Gebiet; insbesondere in den letzten fünf Jahren konnten bemerkenswerte Fortschritte erzielt werden. Die Vielfalt der verwendeten Ansätze und damit verbundenen Möglichkeiten und Herausforderungen ist überwältigend. Dieser Beitrag bietet einen kritischen Überblick über den aktuellen Sachstand auf diesem Gebiet der DFB, mit Fokus auf die additiven Fertigungsverfahren mit Beton (auch 3D‐Betondruck genannt) und formuliert den bestehenden Forschungsbedarf. Neben einer Reflektion zum internationalen Stand der Entwicklung von 3D‐Betondruckverfahren wird ein Klassifizierungsrahmen für DFB‐Verfahren vorgestellt und die wichtigsten Begriffe definiert. Anschließend befassen sich die Autoren mit der zugehörigen Materialprüfung von druckbarem bzw. gedrucktem frischem, erhärtendem und erhärtetem Beton. Einen weiteren Schwerpunkt bilden die Beschreibung der geeigneten Bewehrungsarten und die Klassifizierung der technologischen Lösungsansätze zur Integration der Bewehrung in DFB‐Prozesse. Schließlich werden die Besonderheiten der Konstruktion und die Bemessung von additiv gefertigten Bauteilen dargelegt und diskutiert.

The selective paste intrusion (SPI) describes a selective binding, additive manufacturing method. SPI bonds thin layers of aggregate by cement paste locally. Currently, SPI can achieve higher compressive strength, durability, and easier unpacking behavior compared to other selective binding methods suitable for the production of concrete structures. Particle-bed based methods not only achieve much higher surface resolutions than depositing (extrusion)-based additive manufacturing methods but also have no restrictions in freedom of form. However, the mechanical performance of SPI components strongly depends on the void content between the individual layers and thus the penetration behavior of the cement paste. This paper presents direction-dependent measurements of the strength and durability of SPI-printed components compared to casted specimens with the same mixing composition. The results show compressive strength values between 70 and 78 MPa after 7 d, flexural strength of 1/10 without reinforcement, a high freeze–thaw resistance, no detectable carbonation after 182 days of exposure under ambient CO2–conditions, and after 28 days under increased CO2 content of 2 vol % as well as low chloride penetration resistances. All tests showed in almost all cases no dependency on the layer orientation.

After only a few years of intensive research all over the world, 3D printing of buildings has become possible. However, existing design codes do not cover all the special technical features of the new construction method. Therefore, it is necessary to develop supplementary and adapted test procedures as well as design standards. In addition, a building permit (approval for individual case) must be issued. In this paper, we describe a concept to obtain an approval for individual case for the construction of the first 3D-printed detached house in Beckum, Germany, following existing standards for concrete and masonry construction. To choose the right test methods, one must know the design of the building, the additive manufacturing technique, the material, and the production environment. In the presented case, the house was completely built on the building site. The design of the house used 3D-printed parts for inner and outer walls for load-bearing and non-load-bearing elements. For this purpose, material properties such as setting, direction-dependent strength, and durability were tested. However, due to the scope of the paper, only flexural strength measurements are addressed here. All investigations focused on the formation of cold joints due to breaks in the construction process and the environmental impact. However, due to scale effects, testing of large-scale elements was necessary. In particular, larger wall elements showed decreased flexural strength compared to smaller specimens (prisms). Therefore, we present a concept for testing the load-bearing performance of wall elements and their resistance to the pressure of fresh concrete. All tests were successfully applied, characteristic design values were provided, the approval for individual case was granted, and the construction process began.

Digital concrete construction by means of additive processes - State of the art and research needs Digital fabrication with concrete (DFC) is a dynamic and rapidly developing area. In the last five years in particular, remarkable progress has been made. The variety of approaches used and both the opportunities and challenges associated with them is overwhelming. This contribution offers a critical overview of the current state of the art in the field of the DFC, with a focus on the additive manufacturing processes with concrete (also called 3D concrete printing) and formulates the research needs. In addition to a reflection on the international state of the development of 3D concrete printing technologies, a classification framework for DFC processes is presented and the most important terms are defined. Then, the authors deal with the material testing of printable or printed fresh, hardening and hardened concrete. Futher focuses are the suitable types of reinforcement and the classification of the technological approaches to integrate reinforcement in DFC processes. Finally, the special features of the design and dimensioning of additively manufactured components are presented and discussed.

Extruded lightweight aggregate concrete (LAC) enables to unite static and building physics properties within monolithic structures. Besides, material demand can be reduced according to necessity. However, the contradicting requirements in extrusion for pumpability and buildability are intensified compared to normal concrete due to the change of LAC fresh properties during pumping. This paper focusses on the effect of cement type and amount of limestone powder on the pumpability of LAC at comparable buildability. We show that the pumping performance enhances with increasing limestone powder content. Furthermore, we find that the increase in density during the pumping process is affected by the water retention of the material, which in turn correlates with the limestone powder content. The resulting strength can thus be consciously improved. The amount of limestone powder has only a minor effect on structural build-up and static yield stress and thus, on buildability. However, we find a general strong increase in static yield stress during pumping of LAC, which further facilitates the buildability in addition to the positive effect of the low density of LAC resulting in reduced weight loads to bear during extrusion. Another advantage is that reasonable replacement of cement by limestone powder leads to less drying shrinkage without significantly reducing the strength. Concluding, the requirements for extrusion of LAC – for both pumpability as well as buildability – can be fulfilled and adjusted to necessity by partly substitution of the cement with limestone powder.

Lightweight mortar extrusion enables the production of monolithic exterior wall components with improved thermal insulation by installing air chambers and reduced material demand compared to conventional construction techniques. However, without reinforcement, the systems are not capable of bearing high flexural forces and, thus, the application possibilities are limited. Furthermore, the layer bonding is a weak spot in the system. We investigate a reinforcement strategy combining fibers in the mortar matrix with vertically inserted elements to compensate the layer bonding. By implementing fibers in the extruded matrix, the flexural strength can be increased almost threefold parallel to the layers. However, there is still an anisotropy between the layers as fibers are oriented during deposition and the layer bond is still mainly depending on hydration processes. This can be compensated by the vertical insertion of reinforcement elements in the freshly deposited layers. Corrugated wire fibers as well as short steel reinforcement elements were suitable to increase the flexural strength between the layers. As shown, the potential increase in flexural strength could be of a factor six compared to the reference (12 N/mm2 instead of 1.9 N/mm2). Thus, the presented methods reduce anisotropy in flexural strength due to layered production.