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Three-dimensional printable concrete (3DPC) has become increasingly popular in the building and architecture industries due to its low cost and fast design. Currently, there is great interest in the mix design methods and mechanical properties of 3DPC, particularly in relation to yield stress analysis. The ability to extrude and build 3D-printed objects can be significantly affected by factors such as the rate of extrusion, nozzle size, and type of pumps used. It has been observed that a yield stress lower than 1.5 to 2.5 kPa is not sufficient to maintain the shape stability of concrete, while a yield stress above this range can limit the material's extrudability. Furthermore, the strength properties of 3DPC are influenced by factors such as changes in yield stress and superplasticiser dosages. To meet the high mechanical strength and durability requirements of 3DPC in the construction industry, it is essential to analyse the material's early-age mechanical properties. However, the development of standardised test methods for 3DPC is still deficient. To address this issue, a bibliometric analysis was conducted to comprehensively review the diverse test methods and mechanical characteristics of 3DPC with different mix proportions. To produce high-performance concrete from various additives and waste materials, it is critical to have a basic understanding of the hydration processes of 3DPC. Moreover, a detailed analysis of the environmental impact and energy efficiency of 3DPC is necessary for its widespread implementation. This review article will highlight the recent trends, upcoming challenges, and benefits of using 3DPC. It serves as a taxonomy to navigate the field of 3DPC towards sustainable development. [ABSTRACT FROM AUTHOR]

Despite all the recent advances in the development of threedimensional (3-D) concrete printing (3DCP), this technology still has many unresolved problems. In most of the completed projects with the application of 3DCP, the focus was mainly on mastering the printing of vertical walls, while horizontal structural elements were produced with conventional methods--that is, using formwork, which reduces the level of technology automation, or using prefabricated elements, which makes the construction dependent on their availability and supply. In this contribution, the authors propose new methods of manufacturing slabs and beams directly on site by extruding concrete onto a textile reinforcement mesh laid on a flat surface. Specimens obtained from a slab produced following this method were used for mechanical testing and investigation of the concrete-reinforcement interface zone. Finally, as proof of the feasibility of the proposed approach, a demonstrator representing a full-scale door lintel was manufactured. [ABSTRACT FROM AUTHOR]

This paper proposes an effective approach to realise circular construction with concrete, and shows Unreinforced Masonry as a foundational building block for it. The paper outlines the importance of circularity in building structures. It specifically focuses on the impact of circular construction with concrete on improving the sustainability of the built environment in a rapidly urbanising world economy. Subsequently, the relevance of principles of structural design and construction of unreinforced masonry to achieve circularity is articulated. Furthermore, the paper presents and summarises recent developments in the field of Unreinforced Concrete Masonry (URCM) including digital design tools to synthesise structurally efficient shapes, and low-waste digital fabrication techniques using lower-embodied-emission materials to realise the designed shapes. The paper exemplifies these using two physically realised, full-scale URCM footbridge prototypes and a commercially available, mass-customisable building floor element, called the Rippmann Floor System (RFS). The paper also outlines the benefits of mainstream, industrial-scale adoption of the design and construction technologies for URCM, including accelerating the pathway to decarbonise the concrete industry. In summary, the paper argues that URCM provides a solution to significantly mitigate the carbon emissions associated with concrete and reduce the use of virgin resources whilst retaining its benefits such as widespread and cheap availability, endurance, fire safety, low maintenance requirements and recyclability. [ABSTRACT FROM AUTHOR]

Three-dimensional printable concrete (3DPC) has become increasingly popular in the building and architecture industries due to its low cost and fast design. Currently, there is great interest in the mix design methods and mechanical properties of 3DPC, particularly in relation to yield stress analysis. The ability to extrude and build 3D-printed objects can be significantly affected by factors such as the rate of extrusion, nozzle size, and type of pumps used. It has been observed that a yield stress lower than 1.5 to 2.5 kPa is not sufficient to maintain the shape stability of concrete, while a yield stress above this range can limit the material’s extrudability. Furthermore, the strength properties of 3DPC are influenced by factors such as changes in yield stress and superplasticiser dosages. To meet the high mechanical strength and durability requirements of 3DPC in the construction industry, it is essential to analyse the material’s early-age mechanical properties. However, the development of standardised test methods for 3DPC is still deficient. To address this issue, a bibliometric analysis was conducted to comprehensively review the diverse test methods and mechanical characteristics of 3DPC with different mix proportions. To produce high-performance concrete from various additives and waste materials, it is critical to have a basic understanding of the hydration processes of 3DPC. Moreover, a detailed analysis of the environmental impact and energy efficiency of 3DPC is necessary for its widespread implementation. This review article will highlight the recent trends, upcoming challenges, and benefits of using 3DPC. It serves as a taxonomy to navigate the field of 3DPC towards sustainable development.

3D printed concrete is a relatively new technology that has been gaining popularity in the construction industry in recent years. It involves the use of a 3D printer to deposit layers of concrete in a pre-determined pattern, gradually building up a three-dimensional structure. This process offers several benefits over traditional concrete construction methods, such as the ability to create complex geometries and reduce material waste. One of the main advantages of 3D printed concrete is its ability to produce highly customized and unique designs that would be difficult or impossible to achieve using traditional construction techniques. Additionally, the precision of the 3D printing process allows for greater control over the properties of the concrete, such as its strength and porosity, which can be tailored to suit the specific requirements of the project. Another benefit of 3D printed concrete is its potential for sustainability. By minimizing material waste and using eco-friendly materials, this technology has the potential to reduce the environmental impact of construction.

Incorporating coarse aggregate into 3D-printed concrete is essential for promoting its practical application, yet the impact on the early age time-dependent mechanical properties, crucial for the multilayer structure stability and quality, is underexplored. In this study, 3D-printed concrete with coarse aggregate (3DPCA) with varying mortar-to-coarse aggregate ratios (M/A) and coarse aggregate gradations were prepared, of which uniaxial unconfined compression and direct shear performance were experimentally investigated. The fundamental formulations between the early age mechanical parameters and the resting time of 3DPCA were characterized and then utilized in a digital model simulating actual printing. Results indicated that the 3DPCA early age mechanical properties, including compressive strength, Young's modulus, cohesion, and friction angle, increased with longer resting time and decreasing M/A, and higher proportions of aggregates above 9.5 mm. High coarse aggregate content caused three distinct compressive strength-displacement curve stages and complicated strength eigenvalue extraction. Coarse aggregate gradation affected shear properties more than content, with larger aggregates improving cohesion and friction angles. The failure mode prediction model based on ABAQUS could accurately predict the maximum collapse layer of 3DPCA that occurred in overall unstable collapse and over-expansion failure but was incapable of localized deformation. [Display omitted] • Time-dependent mechanical parameters of 3DPCA within 60 min resting time are characterized. • The effect of coarse aggregate content and gradation on the 3DPCA properties are investigated. • A prediction digital model accurately predicts the maximum failure layer of the 3DPCA wall. [ABSTRACT FROM AUTHOR]

Digital concrete is advancing due to growing economic incentives for construction automation. Achieving more sustainable concrete construction requires carbon reduction, and digital concrete technologies enable material-saving designs. By decoupling production strength from design strength, two-component (2K) systems utilizing aluminate precipitation offer the most flexibility, allowing more sustainable mixes with higher substitution levels. However, 2K aluminate systems are complex and demand a deeper understanding of their chemistry and strength buildup. This article reviews the basics of 2K aluminate systems, specifically aluminum sulfate-based and calcium aluminate cement/calcium sulfate-based systems, and their use in an inline active mixing reactor. An example reaction engineering analysis predicts the degree of reaction in a given reactor design, relating it to yield stress. The two chemical systems are compared, and future research recommendations are provided. [ABSTRACT FROM AUTHOR]

This paper explores the opportunities of digital fabrication with concrete (DFC) to improve structural efficiency and achieve sustainable construction. Efficient structural solutions that drastically reduce material consumption can be achieved by ensuring direct load flow and placing material where needed. More than 50 % of material savings can be achieved by using flanges or hollow sections, providing continuity in beams or slabs, reducing the span of structures or using structural systems such as arches, trusses or deep beams. These concepts are not fully exploited as they often require expensive and complex formwork. DFC tackles the latter point, as it promises to produce complex geometries, minimising extra effort, cost, or waste. The paper discusses the optimisation potential of DFC for several structural elements and presents existing applications that demonstrate this potential. Five case studies of different technological approaches are discussed in detail, highlighting advantages and disadvantages to be addressed for widespread adoption. [ABSTRACT FROM AUTHOR]

This study investigates the shrinkage-induced deformation behaviour of 3D-printed concrete, which exhibits unique characteristics compared to traditionally cast concrete. Through a comprehensive analysis, the onset, direction, and magnitude of deformations in 3D-printed elements are analyzed. Leveraging extensive experimental data, both analytical and numerical models were developed to predict these deformations accurately. Developed models demonstrate strong alignment with experimental results, particularly in the case of a 3D-printed concrete wall. The findings provide valuable insights and tools for advancing the understanding and application of 3D-printed concrete in construction. • The shrinkage-induced deformation behaviour of 3D-printed concrete elements differs from that of cast concrete elements. • The deformation behaviour of the 3D-printed elements was described. • 3D-printed concrete elements do not follow the common volumetric strain model. • Thermal expansion may significantly affect the deformation behaviour of 3D-printed concrete elements. • Additionally to the volumetric strains, 3D-printed concrete elements experience a curling at the edges. [ABSTRACT FROM AUTHOR]

Even though computational design has paved the way for the design of complex forms, construction is still difficult, inefficient, and costly. This paper aims to compile the most recent fabrication techniques for shell structures to create an overview of fabrication methods. This paper reviews existing, recently developed, and previously unexplored techniques for building and fabricating shell structures. The objective of this review is to find trends, patterns, or gaps in the literature that can direct future research. As a result, each fabrication technique is explained and demonstrated with relevant built projects. Moreover, each method's advantages, disadvantages, and limitations are highlighted. These techniques are grouped into four main classes and evaluated. In conclusion, categorizing fabrication techniques reveals the state-of-the-art in fabrication and highlights potential research gaps. Moreover, this research might encourage researchers to explore novel methods and solutions to overcome the current method's limitations. • The state-of-the-art fabrication techniques for shell structures are presented. • A comprehensive, up-to-date literature review of fabrication methods is presented. • The methods of fabrication are classified in an exclusive manner. • The pros and cons of fabrication techniques are discussed. • This review highlights the current gaps in fabrication methods. [ABSTRACT FROM AUTHOR]

Concrete is one of the most used materials after water. Largely owing to this, its environmental impact is substantial, although its embodied carbon per unit volume or mass is low when compared to most alternatives. This, along with the broad availability, good strength, durability and versatility of concrete means that it will remain a material of choice, although more efficient ways of using it must be found. Structurally optimized building components are a means to do this as they can save about 50% material. Unfortunately, however, such elements are presently too expensive to produce owing to them requiring non-standard formwork. It is an objective of digital fabrication to propose solutions to this issue. In this con-text, Digital Casting Systems (DCS) have advanced material control strategies for setting-on-demand in digital concrete processing. Thereby, the formwork pressure is reduced to a minimum, which opens possibilities of rethinking formworks as systems that are dynamically shaping, millimetre thin or weakly supporting the material cast inside. In this paper we present a brief overview of millimetre thin formworks and summarize the first realization of concrete elements that utilizes the mechanics of paper folding to make millimetre thin formworks up to 2.5 meters high. Such formworks could initially be flat packed, erected into shape, and eventually peeled-off and recycled in established material streams. This would reduce waste and transport cost, while offering a surface finish that meets the expectations for exposed concrete surfaces.

The concrete used in floor slabs accounts for large greenhouse gas emissions in building construction. Solid slabs, often used today, consume much more concrete than ribbed slabs built by pioneer structural engineers like Hennebique, Arcangeli and Nervi. The first part of this paper analyses the evolution of slab systems over the last century and their carbon footprint, highlighting that ribbed slabs have been abandoned mainly for the sake of construction time and cost efficiency. However, highly material-efficient two-way ribbed slabs are essential to reduce the environmental impact of construction. Hence, the second part of this paper discusses how digital fabrication can help to tackle this challenge and presents four concrete floor systems built with digitally fabricated formwork. The digital fabrication technologies employed to produce these slab systems are digital cutting, binder-jetting, polymer extrusion and 3D concrete printing. The presented applications showcase a reduction in concrete use of approximately 50% compared to solid slabs. However, the digitally fabricated complex formworks produced were wasteful and/or labour-intensive. Further developments are required to make the digital processes sustainable and competitive by streamlining the production, using low carbon concrete mixes as well as reusing and recycling the formwork or structurally activating stay-in-place formwork.

Concrete construction harms our environment, making it urgent to develop new methods for building with less materials. Structurally efficient shapes are, however, often expensive to produce, because they require non-standard formworks, thus, standard structures, which use more material than is often needed, remain cheaper. Digital fabrication has the potential to change this paradigm. One method is Digital Casting Systems (DCS), where the hydration of self-compacting concrete is controlled on the fly during production, shortening the required setting time and reducing hydrostatic pressure on the formwork to a minimum. This enables a productivity increase for standard concrete production. More importantly, though, it enables a rethinking of formworks, as the process requires only cheap thin formworks, thus, unlocking the possibility to produce optimised structural members with less bulk material and lower environmental cost. While DCS has already proven effective in building structural members, this process faces the challenge of moving into industry. This paper covers the next steps in doing so. First, we present the benchmark and expectations set by the industry. Second, we consider how we comply with these requirements and convert our fast-setting self-compacting mortar mix into a coarser one. Third, we present the next generation of our digital processing system, which moves closer to the industrial requirements in terms of size and the control system. Finally, two prototypes demonstrate how DSC: (a) increases standard bulk production by 50% and (b) can be cast into ultra-thin formworks. We discuss the results and the short-term industrial concerns for efficiency and robustness, which must be addressed for such a system to be fully implemented in industry. [ABSTRACT FROM AUTHOR]

3D printed concrete is a relatively new technology that has been gaining popularity in the construction industry in recent years. It involves the use of a 3D printer to deposit layers of concrete in a pre-determined pattern, gradually building up a three-dimensional structure. This process offers several benefits over traditional concrete construction methods, such as the ability to create complex geometries and reduce material waste. One of the main advantages of 3D printed concrete is its ability to produce highly customized and unique designs that would be difficult or impossible to achieve using traditional construction techniques. Additionally, the precision of the 3D printing process allows for greater control over the properties of the concrete, such as its strength and porosity, which can be tailored to suit the specific requirements of the project. Another benefit of 3D printed concrete is its potential for sustainability. By minimizing material waste and using eco-friendly materials, this technology has the potential to reduce the environmental impact of construction. [ABSTRACT FROM AUTHOR]

Concrete construction harms our environment, making it urgent to develop new methods for building with less materials. Structurally efficient shapes are, however, often expensive to produce, because they require non-standard formworks, thus, standard structures, which use more material than is often needed, remain cheaper. Digital fabrication has the potential to change this paradigm. One method is Digital Casting Systems (DCS), where the hydration of self-compacting concrete is controlled on the fly during production, shortening the required setting time and reducing hydrostatic pressure on the formwork to a minimum. This enables a productivity increase for standard concrete production. More importantly, though, it enables a rethinking of formworks, as the process requires only cheap thin formworks, thus, unlocking the possibility to produce optimised structural members with less bulk material and lower environmental cost. While DCS has already proven effective in building structural members, this process faces the challenge of moving into industry. This paper covers the next steps in doing so. First, we present the benchmark and expectations set by the industry. Second, we consider how we comply with these requirements and convert our fast-setting self-compacting mortar mix into a coarser one. Third, we present the next generation of our digital processing system, which moves closer to the industrial requirements in terms of size and the control system. Finally, two prototypes demonstrate how DSC: (a) increases standard bulk production by 50% and (b) can be cast into ultra-thin formworks. We discuss the results and the short-term industrial concerns for efficiency and robustness, which must be addressed for such a system to be fully implemented in industry.

The creation of concrete shells from customized prefabricated modules is a novel approach that facilitates the construction of free-form surfaces considerably. In the framework of the Adaptive Concrete Diamond Construction (ACDC) project at TU Dresden, a material for 3D printing of the outer contours of such modules has been developed based on the principles of Strain Hardening Cementitious Composite (SHCC). In addition to its high ductility, the required material must also be suitable for 3D printing while enabling the achievement of high geometric accuracy in the manufacture of the modules. To gain the required performance, cellulose ether and starch ether were used specifically to extend the open time, for a longer period of maintaining initial workability, as well as for enhancing shape stability and surface quality. An extensive experimental program was carried out to evaluate the outcomes of the material modifications, including flow table tests, water retention tests, and several specific tests to determine the adhesiveness of the fresh SHCC. For hardened SHCC, surface roughness was assessed using a laser 3D scanner in addition to testing its mechanical properties.

• Empirical and numerical measurements of the shrinkage strains of the 3D-printed concrete elements before solidification. • Thin 3D-printed walls are more susceptible to PS and resulting cracking than elements printed with coarse filaments. • Various parameters may affect the accuracy of numerical simulation. • Simplification of the 3D numerical model into a 2D one. • Stepwise guidance for setup of the numerical simulation. In the initial hours following extrusion, 3D-printed concrete elements undergo intensive water evaporation. This process leads to significant negative capillary pressure within the system. During the period before solidification, this capillary pressure induces volumetric contractions, commonly referred to as plastic shrinkage, in the 3D-printed concrete, and as a result, causes cracking. Therefore, managing and forecasting the negative capillary pressure in freshly deposited concrete filaments is crucial to mitigating the effects of plastic shrinkage. In this study, the progression of capillary pressure in 3D-printed elements, with filament thickness ranging from 37.5 mm to 150.0 mm, was experimentally evaluated and numerically simulated. The numerical simulations utilised the extended Richard's equation. Shrinkage strains were empirically measured using 3D digital image correlation and compared with numerical outcomes. Additionally, we examined various combinations of parameters to analyse their influence on the accuracy of the numerical results. [ABSTRACT FROM AUTHOR]

The adoption of digital fabrication with concrete (DFC) has the potential to bring sustainability, productivity, and process innovation to the construction industry. However, DFC adoption towards market-ready construction systems is lagging due to a lack of understanding in matching its technology capabilities with the needs of potential adopters. This paper describes a DFC Evaluation Framework, analyzing current advancements in DFC through a Conceptual Framework Analysis. The framework is focused on the inputs, process parameters and outcomes of a given technology solution independently of the enabling technology type. It can be used to classify and compare DFC technologies along their systemic characteristics, which are both technical and non-technical in nature. The DFC Scoreboard, an interactive tool to match DFC technologies with the needs of prospective adopters, is developed and tested based on the framework. The paper discusses how the DFC Evaluation Framework and Scoreboard offer one of the first systemic overviews of DFC adoption, with the capability to match technology capabilities and user needs in the technology adoption process. • Digital fabrication with concrete lacks guidance matching technologies with adopter needs. • Conceptual framework of categories for industry adoption of digital fabrication with concrete. • Interactive tool to match technology potential and needs of adopters in the construction industry. • Implications of the interactive evaluation tool for adoption of digital construction methods. [ABSTRACT FROM AUTHOR]