3D Concrete Printing Research Articles

Computational fluid dynamics modelling and experimental analysis of reinforcement bar integration in 3D concrete printing

A challenge for 3D Concrete Printing is to incorporate reinforcement bars without compromising the concrete-rebar bonding. In this paper, a Computational Fluid Dynamics (CFD) model is used to analyze the deposition of concrete around pre-installed rebars. The concrete is modelled with a yield-stress dependent elasto-viscoplastic constitutive model. The simulated cross-sections of the deposited layers are compared with experiments under different configurations and rebar sizes, and found capable of capturing the air void formation with high accuracy. This proves model robustness and provides a tool for running digital experiments prior to full-scale tests. Additionally, the model is employed to conduct a parametric study under three different rebar-configurations: i) no-rebar; ii) horizontal rebar; and iii) cross-shaped (horizontal and vertical) rebars. The results illustrate that air voids can be eliminated in all investigated cases by changing the toolpath, process parameters, and rebar joint geometry, which emphasizes the great potential of the digital model.

Selecting the Best 3D Concrete Printing Technology for Refugee Camp’s Shelter Construction Using Analytical Hierarchy Process: The Case of Syrian Refugees in Jordan

Upgrading the Syrian refugee shelter design serves humanitarian needs, especially since the currently used T-shelters have a life span of 2–4 years, and there are no clear signs of an imminent return of Syrian refugees to their country, even after the end of the civil war. The use of 3D concrete printing can provide a promising method to construct new durable shelters with a long life span and provide better protection against extreme change in the desert climate, privacy, and cultural constraints. This research aims to use multi-criteria decision methods—in particular, the Analytical Hierarchal Process (AHP) method—to select the best 3D concrete printing to construct these shelters. The proposed model takes the following into consideration: the machine’s technical characteristics, building structure characteristics, and economic and environmental aspects. The three basic developed technologies—contour crafting, D-shape, and concrete printing—were used as alternatives in the model. The results show that contour crafting is the best technology for this application, and the inconsistency test and sensitivity analysis indicate an effective and reasonable technology ranking.

Investigation of a shotcrete accelerator for targeted control of material properties for 3D concrete printing injection method

The efficiency of 3D concrete printing significantly depends on the mortar performance, which can be improved and controlled by adding a shotcrete accelerator. This targeted control is implemented by adding a small accelerator dose to an injection nozzle before extrusion. In this article, a study is conducted on the suitability of the material for this application. For this purpose, a shotcrete accelerated printable mortar is investigated. Comparing physical and physicochemical results leads to an in-depth understanding of the chemical processes and their effects on physical behaviour, which enables a positive assessment of the accelerator for 3D concrete printing injection method.

Designing a Habitat for 3D Concrete Printing in Permafrost Regions

3D concrete printing has the potential to provide solutions to the global shortage of affordable housing. The technology may be particularly suitable for remote regions, where the shortage of labor and materials present challenges. While most projects have focused on the use the technology to fabricate a structure’s walls, this article describes a research effort aimed at printing the entire structure, including the enclosing surface using only 3D concrete printing. The design of a habitat for the permafrost regions of Alaska is used as a case study. The design approach was to conceive a parametric housing system based on modular units whose form are inspired by traditional vault design and amenable to 3D concrete printing. The proposed design is based on features and reach of the robotic arm printer, the desire to avoid formwork, withstanding applicable loads on the structure, and thermal requirements. While the size of each modular unit is determined by spatial requirements, its exact shape is defined using optimization following structural, thermal, and printing considerations. The printing of a reduced-scale version of the proposed unit validated the design showing its printability.

Concrete Additive Manufacturing in Construction: Integration Based on Component-Related Fabrication Strategies

Additive manufacturing (AM) with concrete, also known as concrete 3D printing, is one of the most interesting approaches for disrupting the construction industry and is currently subject to numerous research activities worldwide. AM has great potential to decrease labour costs and increase the material efficiency and geometric complexity of non-standardised building components. Although prior investigations have shown various fields of application for AM with concrete, the full potential with respect to different structural component types has not been covered yet. With this paper, an up-to-date review of fabrication strategies for the main structural components, (1) walls, (2) columns, (3) slabs, and (4) beams, is provided to identify trends and existing challenges. Therefore, firstly, AM methods and their underlying principles and characteristics for concrete components are presented, and secondly, fabrication strategies for each AM method are shown. The investigation uncovers different AM strategies (direct part vs. indirect “permanent formwork”; in situ, on-site, or off-site), which are currently being used. As a result, future applications of AM will require a hybrid manufacturing strategy combining conventional and additive manufacturing to fully explore its potential.

Buildability analysis on effect of structural design in 3D concrete printing (3DCP): An experimental and numerical study

The importance of numerical modeling and simulation approaches increases with increased scale as it allows for early results predictions. This study evaluated the buildability of novel construction and demolition waste (CDW)-based geopolymer materials for 3-dimensional printing (3DP) structures for the built environment. The feasibility of the developed numerical model for 3DP of built environment structures was also evaluated. This study reported the fresh-state properties of geopolymer-based materials, and based on these results, numerical modeling for 3DP of geopolymer material was performed. Three cylindrical structures with diameters of 300 mm, 450 mm, and 600 mm were printed, with the same printing conditions, resulting in buildability of 352.5 mm, 322.5 mm, and 277.5 mm (total height constructed before the collapse), respectively. In the next stage of the study, a comparative analysis was performed to assess the compatibility of numerical models for CDW-based geopolymer materials. In the numerical results, three structures showed early failure prediction from experimental results at 31.91%, 29.10%, and 29.73%, respectively. The geopolymer materials developed were suitable for 3DP, and close agreement in results and repeatability were observed. The numerical model provided a reliable failure prediction for different structures. Hence, the model can be utilized to evaluate the buildability of the structures before the actual 3DP, which can significantly reduce the time and cost of the project.

Structural design and engineering of Striatus, an unreinforced 3D-concrete-printed masonry arch bridge

This paper describes the structural design and engineering of “Striatus”, a 3D-concrete-printed unreinforced masonry pedestrian bridge built in Venice in 2021 as part of the Time Space Existence exhibition organised by the European Cultural Centre. The project combines the latest developments in 3D concrete printing with the structural principles of historic unreinforced masonry. Typically, the structural applications of 3D concrete printing are limited to elements such as columns and walls loaded vertically, perpendicularly to the horizontal printing layers, to formwork elements or secondary structural elements. Indeed, fabrication constraints, delamination issues and the low tensile strength of the concrete have been seen as limiting factors to 3D concrete printing for structural applications demanding resistance to bending or predominant loading directions not perpendicular to the printing layers. By using unreinforced-masonry structural principles, this paper shows that structural elements spanning space horizontally, such as a pedestrian bridge, can be built by using the 3D concrete printing components as the main structure, working only in compression, loaded perpendicularly to the printed layers. Furthermore, as a compression-only structure following masonry principles, Striatus enabled the use of unreinforced concrete without any mechanical or chemical connections between the elements and the separation of concrete and steel, only used for the supports and to equilibrate the horizontal thrust of the arch effect through the tension ties. This work shows how the application of unreinforced masonry principles to 3D concrete printing offers new opportunities in terms of structural design and represents a strategy to increase sustainability by reducing material consumption and allowing reusability and recyclability of the structure. Finally, this paper discusses the critical aspects related to the design of Striatus from an engineering and construction point of view.

On the possibility of using waste disposable gloves as recycled fibers in sustainable 3D concrete printing using different additives

Due to the Covid-19 pandemic, using large amounts of personal protective equipment (PPE) throughout the world has extensively increased in recent years. The lack of a practical method to dispose of these recycled materials is one of the main concerns of researchers. Hence, comprehensive experimental tests were conducted in the present study to investigate the feasibility of using disposable gloves in mortars to achieve a sustainable mixture. Accordingly, latex and vinyl gloves as recycled fibers were considered in the experimental program to improve the sustainability of 3D printing concrete. As using these recycled materials causes some deficiencies for printing layers, different mineral and chemical admixtures were used in the present study, including graphene oxide nanomaterials, polyvinyl alcohol, Cloisite 15A nanoclay, and micro silica fume. Also, the hybrid use of latex, vinyl, and polypropylene (PP) fiber was considered to improve the printability of concrete mixtures containing waste fibers. Moreover, the effect of internal reinforcement was also considered by using plain steel wire mesh to increase the composite behavior of printed layers in this simplified experimental program. Results indicate that the synergic influence of recycled fibers and admixtures meaningfully enhanced the 3D printing properties of mortar so that about 20%, 80%, 50%, and more than 100% improvements were obtained for workability, direct tensile strength, flexural strength, and buildability index respectively. However, an average percentage − 28.3% reduction was recorded for the concrete compressive strength. Sustainability analysis also showed that using waste disposable gloves considerably reduced CO2 emissions.

Effect of anisotropy on permeability index and water absorption of 3D printed metakaolin-based geopolymer concrete

3D-printed geopolymer concrete (3DPGPC) is being showcased as a potential alternative to ordinary Portland cement concrete in digital construction. However, the widespread application is limited due to the unknown long-term durability properties of the material, which could also be influenced by the anisotropic behaviour of the prints. The durability index (DI) of metakaolin (MK) based 3DPGPC and mould-cast specimens from mixes modified with 0% and 5% slag and reinforced with 0.5% polypropylene fibre by volume are investigated using the oxygen permeability index (OPI) and water absorption test. 70 mm diameter by 30 mm thick specimens were cored perpendicular (D3-horizontal and D2-vertical) to the printing direction. OPI specimens were cured for 28 and 90 days, respectively, in the climate-controlled room at 23 (±2°C) and 65 (±5%) relative humidity. 7 days before curing elapsed, specimens were placed in the oven and maintained at 50 ℃. Specimens were removed from the oven and cooled to 23 (±2°C) in the desiccator for 2 h before placing them in the permeameter cell for testing at 28 and 90 days of curing following SANS-3001-CO3-3 (2015). The OPI test comprised the supply of oxygen at the pressure of 120 kPa to the permeameter cell and testing terminated when the pressure dropped to 50 kPa. Also, the water absorption of mould cast and 3DPGPC specimens were determined following ASTM D570. The water absorption and permeability coefficients of 3DPGPC are compared with mould-cast to contextualise the durability of 3DPGPC. Slag inclusion reduced the permeability index of mould-cast and 3DPGPC at 28-and 90-day curing ages. However, mould-cast specimens had better OPI performance than 3DPGPC. D3 specimens are less permeable than D2. Also, mould-cast specimens exhibited lower water absorption characteristics than printed specimens. The OPI and water absorption tests indicate different migration characteristics under one-dimensional ingress in 3DPGPC in orthogonal directions.

Space-filling and print path generation methods for large-area 3D concrete printing pavements

3D concrete printing (3DCP) technology is a construction method that offers a unique combination of automation and customization. However, when the printing area goes large, generating the print path becomes a sophisticated work. That’s because the customized print path should not only be expandable but also printable, such rules are hard to follow as both the printing area and construction requirements increase. In this paper, the Shenzhen Baoan 3D Printing Park project serves as a case study to introduce space-filling and print path generation methods for three types of large-area concrete pavement. The space-filling methods utilize geometry-based rules to generate complex and expandable paving patterns, while the print path generation methods utilize construction-oriented rules to convert these patterns into print paths. The research provides easy-to-operate design and programming workflows to achieve a pavement printing area of 836 sqm, which significantly increases the construction scale of large-format additive manufacturing (LFAM) and shows the potential of 3D printing technology to reach non-standard results by using standard workflows.

Comparison of physical and physicochemical methods for 3D printing application with the focus on the unconfined uniaxial compression test

For a commercial success of 3D concrete printing, standardisation is necessary to enable industrial production. To select methods for standardisation from the material side, detailed knowledge of suitable methods and of material behaviour is required in advance. Therefore, this study aims to compare different methods for investigating stiff printable mortars during the transition regime of a non-Newtonian fluid to a cohesive frictional material by physical and physicochemical methods focusing on the unconfined uniaxial compression test. The study shows that all methods exhibit comparable progressions, although the results are affected differently by self-heating, material composition and progressive hydration.

The Development of Soil-Based 3D-Printable Mixtures: A Mix-Design Methodology and a Case Study

Concrete 3D printing is one of the newest technologies in the field of construction. However, despite the various opportunities that this technique offers today, it still has a high environmental impact, as most 3D-printable materials contain high amounts of cement. On the other hand, due to the large volumes of soil excavated each year across the world, there is a pressing need for proper management to dispose of it or reuse it efficiently. This study aims to develop sustainable and resistant 3D-printable materials with low environmental impact using excavated soil. Firstly, a series of tests were carried out to find the most appropriate superplasticizer and the amount required to develop the printable mixtures. Next, the extrudability and buildability were evaluated and verified to validate the printability of the developed mixtures. A 3D laboratory printer was also used to validate the printability of the mixtures on a larger scale. Then, the fresh and hardened properties of the printable mixtures were investigated. Three printable mixtures were developed, with the most environmentally friendly mixture having a soil content of 1602 kg/m3 and a cement content of 282 kg/m3. The mixtures demonstrated satisfactory characteristics and properties in both fresh and hardened states. On the one hand, the mixtures were extrudable and buildable at two laboratory scales. On the other hand, the mixtures presented sufficient compressive strengths, ranging from 16 MPa to 34 MPa, despite their high soil content and low cement content. In addition, their compressive strengths were found to be higher than the minimum strength required for structural concrete. Consequently, this study highlights the possibility of developing ecological, sustainable and resistant mixtures that can be used in 3D-printing construction applications using excavated soil.

A guided approach for utilizing concrete robotic 3D printing for the architecture, engineering, and construction industry

The emerging field of robotic 3D printing offers practical alternatives to conventional building methods that are currently used in the Architecture, Engineering, and Construction (AEC) industry. Robotic 3D printing has many advantages over the conventional construction as it reduces human error, is relatively inexpensive, and opens the door to the creative complex designs while reducing the amount of expertise required to complete the construction process. At present, there is a shortage of resources offering guidance on how to utilize the available technology. Thus, it is often difficult for researchers and practitioners alike to find the right information and make informed decisions relative to their specific applications. In this paper, we provide such a resource by gathering data from previously constructed projects in the form of a categorical study, which paves the way for accessing the most recent information regarding the robotic 3D printing technology of interest. We illustrate the latest methods and techniques used in the field and describe the hardware used. We also use the resulting classification methods to present a decision-making workflow to streamline the process of selecting the most appropriate approach. We also examined and performed a detailed analysis on three case studies of prominent buildings that have been constructed using 3D printing technology. The categorical parameters were selected carefully to form a clear, informative distinction between the buildings. Printing method and motion type were the most important parameters when it comes to robotic 3D printing. A new database was created and demonstrated to elucidate the types of the additive manufacturing that can be used. By analyzing the data, we hope to facilitate the development of new structures as they relate to 3D printing in the AEC industry.

Sustainable Non-Conventional Concrete 3D Printing—A Review

In this review article, system materials for concrete 2D printing have been discussed, along with the various other aspects that are connected to sustainable construction. The article consists of an introduction giving the background of manufacturing that started almost two decades ago, including the non-conventional methods of building structures. It has been seen that there are various stainable materials in the field of 3D printing in construction, as the conversion of construction to 3D printing reduces waste generation. Further in this article, the cost comparison between conventional and non-conventional construction methods has been discussed, including the effectiveness of 3D printing; 3D printing is very effective in the sense that it requires the precise use of machinery and construction material. Full-scale 3D printing has also been seen in the building sector, but only to some extent. Some of the components of bridges, and even some of small bridges, have been constructed using 3D printing and ultra-high-performance concrete. Since there are various advantages to 3D building, there are also various disadvantages to 3D printing, such as how much it costs and finding the materials that are suitable for 3D printing, which might increase the cost. Polymers have also been used in 3D printing construction since polymers have a very long lifespan, and polymers may increase the strength of the final product by reinforcing the aggregate. Additionally, this technology gives us the opportunity to use various materials together for construction, such as recycled aggregates and geopolymers, along with concrete and cement, which might pose some challenges but are being used nowadays. A major concern with this technology is its impact on the labor market. Since in traditional construction huge amounts of man hours are required, concerns have been raised about the inclusion of this technology, as this might affect employment. Since most of the work will be done by machines, the need for labor will reduce. These are some of the issues that need attention. Finally, this article discusses the novelty and future scope of 3D printing in the construction sector, and concludes by outlining the scope of potential developments for 3D printing concrete by taking into account sustainability.

3D printed concrete walls reinforced with flexible FRP textile: Automatic construction, digital rebuilding, and seismic performance

As numerous impressive large-scale 3D printed concrete structures have been built with 3D concrete printing (3DCP) technology, more attention has been given to the automation, accuracy and reliability of this technology. The concept of Brain-Eyes-Hands Loop (BEH Loop) is defined for use in automatic construction, describing the relationships among design, evaluation, and construction. In this paper, an innovative continuous reinforcement method with fiber reinforced polymer (FRP) flexible textile and Engineered Cementitious Composite (ECC) is presented, that offers an effective solution for the lack of tensile reinforcement and corrosion of steel bars in 3D printed concrete structures. The reinforced 3D printed concrete walls were constructed, evaluated, and tested under quasi-static cyclic loading. By digital rebuilding and geometric evaluation, the printing quality of wall specimens was accessed and ensured. Based on the mechanical tests, the seismic performances of the wall specimens were obtained and found to be mainly bending failure. The proposed reinforcement method was demonstrated for delaying crushing and improving mechanical behaviors. The end column and smaller height-width ratio also showed much improvement in mechanical performance. Compared with the conventional cast concrete wall, the 3DCP wall specimens reinforced by the proposed reinforcement method showed better material utilization efficiency and mechanical properties. Therefore, the 3DCP structures reinforced with flexible FRP textile show great potential for the future use in fully automatic construction of large-scale complex architectures according to the frame of the BEH Loop.

An integrated method of topological optimization and path design for 3D concrete printing

As an advanced construction technology, 3D concrete printing (3DCP) has the advantage of high manufacturing freedom for various freeform structures. The digital design of 3D printing using topology optimization contributes to obtaining the maximum performance potential from manufactured structures. However, most digitally designed structures obtained by topology optimization cannot be directly manufactured using 3DCP owing to various manufacturing constraints that have not yet been considered in the design process. This paper presents an integrated design method for 3DCP by incorporating extrusion-based manufacturing characteristics into the topology optimization algorithm. Topological optimization is based on the solid isotropic material with penalization (SIMP) method owing to its ease of adaptation to multiple constraints. During the optimization iteration, the manufacturing characteristics of nozzle size and path continuity are considered as the design requirements of 3D printed structures to achieve high-quality manufacturing by using intermittent interruption of topology optimization to modify the design variables. Meanwhile, the anisotropic behaviors of material constraints and the volume and Tsai-Wu criterion of design constraints are introduced to obtain the desired mechanical performance with lightweight designs. Moreover, the number of closed regions and overhang angle controls are incorporated to ensure the global path continuity and stable stacking of optimized 3D structures. A concrete arch structure is 3D printed to validate the proposed integrated method, and the removal of breakpoints and short paths and complete filling rate are demonstrated. The integrated method facilitates the engineering application of 3DCP in a high-efficiency and high-quality manner.

Development and Characteristic of 3D-Printable Mortar with Waste Glass Powder

Three-dimensional concrete printing (3DCP) is emerging as an innovative technology and shows promise to revolutionize conventional construction modes. However, the current 3D-printed concrete (3DPC) generally requires higher cement content than conventional concrete to ensure its rheology for printing. From the perspective of cleaner production and reduce carbon emissions, this study explored the feasibility of replacing parts of cement with waste glass powder (WGP, 0%, 20%, 40%, and 60% by mass) and compared the properties of the developed 3DPC, including fluidity (flowable spread), rheology, heat of hydration, buildability, compressive strength, anisotropy, and drying shrinkage. The results showed that less than 40% WGP replacement had limited influence on the initial fluidity and static yield stress, as well as drying shrinkage, of 3DPC. Although the WGP inclusion decreased the compressive strength, it slowed down the fluidity loss and static yield stress increase, which could extend the workable time of the mixture for printing and improve buildability. The 40% WGP replacement was found increase to the buildability of the printing mixture from 150 mm to 155 mm. The printing mixture prepared with 60% WGP reduced the dying shrinkage by 50%. An exponential decay function between the fluidity and static yield stress was established so that the simple fluidity test could be used as an indicator of printability. The findings in this study provided a solution to reduce the consumption of cement in 3DPC, which could contribute to a greener production in the construction industry.

3D-printed concrete shear keys: Design and experimental study

To incorporate 3D-printed concrete (3DPC) for modular construction of large-scale building and infrastructure, it is important to develop interlocks firmly connecting adjacent 3DPC modules and providing sufficient shear resistance to prevent inter-segment slippage. To develop guidelines for design and testing of 3DPC shear key interlocks, this paper proposes a fabrication method of such interlocks and studies various designs of 3DPC shear keys through push-off tests and slant shear tests for specimens with different shear key angles and shear joint inclinations. The experimental study focuses on the effect of these geometrical parameters on joint capacities and failure processes. The tests results showed that a smaller shear key angle slightly improved the shear capacity. The normalized shear stress of 3DPC shear keys was similar or slightly lower than precast concrete shear keys whereas shear capacity equations in the literature significantly underestimated the shear strength of 3DPC shear keys.

Improving structural build-up of limestone-calcined clay-cement pastes by using inorganic additives

In 3D concrete printing, fast structuration is a prerequisite for ideal buildability. This paper aims to study the impact of inorganic additives, i.e., CaCl2 and gypsum, on structural build-up and very early-age hydration of limestone-calcined clay-cement (LC3) pastes within the first 70–80 min. Results show that, increasing the dosage of CaCl2 or gypsum can accelerate storage modulus G' and static yield stress evolution with time, as well as increase chemically bound water (H) content and total specific surface area (SSAtotal). Furthermore, good correlations were found between G' and H content, as well as static yield stress and the ratio of free water content to SSAtotal. The acceleration by CaCl2 can be attributed to stimulating C3S and C3A hydration and promoting crystal formation, i.e., ettringite, portlandite, and Friedel’s salt. Additionally, the increase in gypsum percentage led to a large amount of unreacted gypsum in the system, resulting in an increase in SSAtotal.

Machine Learning-Based Predictive Model for Tensile and Flexural Strength of 3D-Printed Concrete.

The additive manufacturing of concrete, also known as 3D-printed concrete, is produced layer by layer using a 3D printer. The three-dimensional printing of concrete offers several benefits compared to conventional concrete construction, such as reduced labor costs and wastage of materials. It can also be used to build complex structures with high precision and accuracy. However, optimizing the mix design of 3D-printed concrete is challenging, involving numerous factors and extensive hit-and-trail experimentation. This study addresses this issue by developing predictive models, such as the Gaussian Process Regression model, Decision Tree Regression model, Support Vector Machine model, and XGBoost Regression models. The input parameters were water (Kg/m3), cement (Kg/m3), silica fume (Kg/m3), fly ash (Kg/m3), coarse aggregate (Kg/m3 & mm for diameter), fine aggregate (Kg/m3 & mm for diameter), viscosity modifying agent (Kg/m3), fibers (Kg/m3), fiber properties (mm for diameter and MPa for strength), print speed (mm/sec), and nozzle area (mm2), while target properties were the flexural and tensile strength of concrete (MPa data from 25 literature studies were collected. The water/binder ratio used in the dataset ranged from 0.27 to 0.67. Different types of sands and fibers have been used, with fibers having a maximum length of 23 mm. Based upon the Coefficient of Determination (R2), Root Mean Square Error (RMSE), Mean Square Error (MSE), and Mean Absolute Error (MAE) for casted and printed concrete, the SVM model performed better than other models. All models' cast and printed flexural strength values were also correlated. The model's performance has also been checked on six different mix proportions from the dataset to show its accuracy. It is worth noting that the lack of ML-based predictive models for the flexural and tensile properties of 3D-printed concrete in the literature makes this study a novel innovation in the field. This model could reduce the computational and experimental effort required to formulate the mixed design of printed concrete.