Search

This study enhances the efficiency of concrete 3D printing for prefabricated lightweight slabs by implementing lean principles and robotic automation. Benchmarking an existing optimized slab design and simulating a lean robotic cell revealed significant improvements in production time, automation efficiency, quality assurance, cost savings, workspace optimization, and continuous improvement through sensor data collection. The study compares the current manufacturing process with a proposed lean process for a complex octagonal slab design. Assumptions on building dimensions, slab requirements, printing methods, and materials facilitated the analysis. The current process takes 10 hours per slab, including printing, reinforcement placement, and drying. Lean principles aim to reduce waste and boost productivity, enhancing the manufacturing efficiency of prefabricated lightweight slabs. [ABSTRACT FROM AUTHOR]

Purpose – This research explores the role of concrete 3D printing (C3DP) in the development of culturally appropriate housing in Indigenous Reserves in Canada through the design, building and evaluation of the Star Lodge project located in the Siksika Nation of Alberta, Canada. The project aims to assess the potential of C3DP in addressing the escalating housing demands in Indigenous communities in Canada. Design/methodology/approach – The research involved a collaborative and multidisciplinary approach, engaging Blackfoot Elders, Knowledge Keepers from the Siksika Nation, Siksika Housing and Nidus3D. Central to this was the design, build and documentation of the Star Lodge project to analyse the advantages and challenges, guided by weekly meetings and site visits. Findings – The project harnessed C3DP to streamline construction, enhance durability, reduce maintenance costs and enhance the energy performance of the homes. Notable time savings were achieved compared to conventional construction methods. Challenges included developing strategies to overcome extreme cold weather conditions, achieving a consistent concrete mix and integrating conventional construction elements such as drywall construction in interiors. The project served as a platform for collaboration and community participation, shaping the design and construction process while raising awareness of innovative construction techniques in the community. Originality/value – This study provides an evidence-based framework for the evaluation of C3DP technology by analysing the Star Lodge Project, the first C3DP project in Alberta and the largest of its kind in Canada. By addressing housing challenges in Indigenous communities, the research holds broader implications for sustainable development and Indigenous empowerment across Canada.

This paper aims to provide a global snapshot of concrete 3D-printed buildings and to uncover robotic-oriented large-scale fabrication strategies. Therefore, an extensive internet search and literature review was carried out to investigate 3D-printed buildings. In this study, 154 construction projects with 204 buildings were systematically recorded and evaluated from 2013 up to 2023. Using an exploratory mixed-methods approach and a comparative case study analysis, a total of 88 3D-printed buildings were first evaluated descriptively. Thereafter, different existing printing strategies for in situ, on-site, and off-site production were identified, using an iterative approach. In addition to the geographical distribution, the descriptive evaluation also showed the key players as drivers for the spread of the 3D-printing technology and the correlations between printer type, fabrication strategy, and the building size. With regard to the printing strategy, three different approaches for in situ and off-site fabrication can be defined, depending on the printer types and their characteristics (work size and mobility): print-in-one-go, horizontal or vertical segmentation, and the multi-element vs. full-scaled wall strategy. However, the study showed that the data quality was sometimes difficult due to a lack of information and essential details of the printing process and segmentation. [ABSTRACT FROM AUTHOR]

Digital fabrication techniques, in recent decades, have provided the basis of a sustainable revolution in the construction industry. However, selecting the digital fabrication method in terms of manufacturability and functionality requirements is a complex problem. This paper presents alternatives and criteria for selection of digital fabrication techniques by adopting the multi-criteria decision-making technique. The alternatives considered in the study are concrete three-dimensional (3D) printing, shotcrete, smart dynamic casting, material intrusion, mesh molding, injection concrete 3D printing, and thin forming techniques. The criteria include formwork utilization, reinforcement incorporation, geometrical complexity, material enhancement, assembly complexity, surface finish, and build area. It demonstrates different multi-criteria decision-making techniques, with both subjective and objective weighting methods. The given ranking is based on the current condition of digital fabrication in the construction industry. The study reveals that in the selection of digital fabrication techniques, the criteria including reinforcement incorporation, build area, and geometrical complexity play a pivotal role, collectively accounting for nearly 70% of the overall weighting. Among the evaluated techniques, concrete 3D printing emerged as the best performer, however the shotcrete and mesh molding techniques in the second and third positions. [ABSTRACT FROM AUTHOR]

Over the past decade, 3D printing with concrete has been widely adopted worldwide. The primary drivers for this innovation are the reduction in manual labor and the more efficient use of natural resources. New materials that are suitable for 3D printing are developed, which are characterized by rapid setting and robust physical and mechanical properties. In this study, for the first time, ternary gypsum–cement–pozzolanic (GCP) composites were developed and evaluated for use in 3D printing. These composites are associated with durability in water as Portland cement (PC) while maintaining the rapid hardening properties of gypsum. Two types of secondary gypsum—recycled plasterboard gypsum (RG) and phosphogypsum (PG)—were used as the calcium hemihydrate component. The compressive strength test showed that 37 MPa can be achieved, which is comparable to that of traditional PC-based 3D printable mixtures. For the first time in a 3D print test, it was experimentally proved that GCP mixtures have good stability and buildability up to 35 layers. According to Life Cycle Analysis, elaborated material gives a carbon footprint reduction of up to 40%, compared to traditional PC mortar, thus supporting the sustainable use of this innovative composite. [ABSTRACT FROM AUTHOR]

Three-dimensional printing allows accurate geometries to be obtained across a wide range of applications and it is now also moving into the architecture and construction industry. In the present work, a unique binary mix composed of ordinary Portland cement (OPC) and quick-setting cement (QSC) was combined with silica sand aggregate in different proportions for a customized binder jetting 3D printing (BJ3DP) process. Specimens were printed using the blended dry powders and deionized water to determine the impact of the processing variables on the properties of the realized specimens. The results show that the properties are influenced by the binary mix proportions and the layer thickness. The investigation found significant improvement in mechanical performance on increasing the proportion of OPC and optimal conditions were identified with proportions of 35 wt% OPC and 5 wt% QSC. Notable enhancements were also observed as the layer thickness was reduced. [ABSTRACT FROM AUTHOR]

Concrete 3D printing is a promising manufacturing technology for producing geometrically complex structures efficiently and cost-effectively, by eliminating the need for formwork, reducing labor, and minimizing waste. This method has the potential to lower carbon emissions and resource use. However, it does not mitigate the carbon emissions associated with cement production. Nonetheless, utilizing waste materials in concrete 3D printing may reduce concrete carbon emissions and support recycling. This study investigates the use of two industrial waste materials–fly ash (FA) and ground waste glass (GWG)–as partial substitutes for ordinary Portland Cement (PC) in 3D printable cement paste. The chemical composition, particle size distribution, rheological properties, and flexural strength of the mixtures were analyzed. Results show that specimens containing waste materials achieved strengths comparable to traditional cement mixtures. The flexural strength reduction in 3D printed versus cast specimens varied across mixtures: control (66% reduction), FA20 (35%), FA10-GWG10 (35%), GWG10 (32%), FA10 (11%), and GWG20 (4%). Hence, incorporating waste materials in concrete 3D printing is recommended, as it maintains mechanical integrity while promoting recycling and upcycling of industrial waste.

3D concrete printing technology has enabled the construction of full-scale bridges. However, structural carbon emissions due to higher cement content and limitations of embedded reinforcement have limited its widespread adoption. This paper presents a non-reinforced 3D printed concrete box arch bridge and describes its design, construction, dismantlement, and reconstruction, as well as evaluation of the carrying capacity of reconstructed primary arch ring. The bridge adheres to current technical principles and bridge engineering specifications. By taking into account the mechanical anisotropy and primary stress characteristics of the arch, the design negates the need for reinforcement. The study showcases the reusability and potential carbon emission reduction through block printing, on-site assembly, block removal, and secondary usage. The safety of the reconstructed arch bridge was confirmed through an in-situ load test.

This paper aims to provide a global snapshot of concrete 3D-printed buildings and to uncover robotic-oriented large-scale fabrication strategies. Therefore, an extensive internet search and literature review was carried out to investigate 3D-printed buildings. In this study, 154 construction projects with 204 buildings were systematically recorded and evaluated from 2013 up to 2023. Using an exploratory mixed-methods approach and a comparative case study analysis, a total of 88 3D-printed buildings were first evaluated descriptively. Thereafter, different existing printing strategies for in situ, on-site, and off-site production were identified, using an iterative approach. In addition to the geographical distribution, the descriptive evaluation also showed the key players as drivers for the spread of the 3D-printing technology and the correlations between printer type, fabrication strategy, and the building size. With regard to the printing strategy, three different approaches for in situ and off-site fabrication can be defined, depending on the printer types and their characteristics (work size and mobility): print-in-one-go, horizontal or vertical segmentation, and the multi-element vs. full-scaled wall strategy. However, the study showed that the data quality was sometimes difficult due to a lack of information and essential details of the printing process and segmentation.

Numerical modeling and simulation approaches can be used to optimize material combinations, structural design, and process parameters to achieve the desired structural performance of 3D-printed structures. In this study, a novel CDW-based mortar mixture was prepared for the 3D concrete printing (3DCP) process. A square cross-sectional structure was designed and 3D-printed using a lab-scale gantry-type 3D printer for buildability analysis. The geopolymer material was also characterized to obtain time-dependent properties for use in a numerical model capable of predicting the buildability of concrete structures. In the numerical modeling and simulation phase, predictive simulations were performed for experimentally 3D-printed structures to validate the predictability of the numerical model. The numerical model revealed a sound approximation of buildability with an error of 6.3% only. Furthermore, using numerical simulations, sensitivity analyses were performed to evaluate the impact of designed height and 3DCP process parameters (i.e., printing speed and layer width) on the buildability of structures. The numerical modeling and simulation results revealed a strong impact of both process parameters (i.e., printing speed and layer width) on the buildability of 3D-printed structures. A maximum buildability of 410.6mm was achieved for structure 3D-printed at a printing speed of 20mm/s and layer width of 45mm. Overall, an improved buildability was observed for lower printing speeds and higher layer widths; however, the buildability performance was more sensitive to the layer width.

The aim of this study is to question the need for alternative project delivery methods to foster the integration of concrete 3D printing in the construction industry. For this purpose, a literature review was carried out. The results indicate that the traditional planning and construction process will have to be reconsidered. On the one hand, new roles and changes in responsibilities may emerge, and, on the other hand, a holistic design process and early contractor involvement will be required to fully exploit the potential of concrete 3D printing. Therefore, alternative project delivery models need to be adopted. [ABSTRACT FROM AUTHOR]

Utilization of an Electromechanical impedance (EMI) technique with Piezoelectric (PZT) sensors has showed potential for Structural Health Monitoring (SHM). The changes in mechanical structure via flexural bending and cracking can be detected by monitoring the deviations in electrical impedance signals recorded with embedded PZT sensors. This paper has conducted a comprehensive study on the potential of an EMI technique with embedded PZT sensors with 3D Concrete Printing (3DCP) structures subjected to flexural bending test until plastic failure. The impact of different Piezoelectric housing methods and materials has been studied comprehensively through the monitoring of EMI signals. Experimental results indicate that material housing types and thickness affect the sensitivity of EMI readings but also performed as a reinforcement when a load is directly applied. The embedded PZT sensors with the EMI technique have shown strong potential to address the cost and lifecycle challenges posed by traditional construction methods as the insertion of PZT sensors seamlessly functions with 3DCP workflows. Further developmental work can be carried out to address the sensitivity of the sensor, performance as a reinforcement, and installation automation. The results proved that the coated sensors could detect fractures in 3DCP concrete with decreased sensitivity on thicker coating layers through the variance in materials and coating thickness in the paper. [ABSTRACT FROM AUTHOR]

We propose a new numerical method to analyze the early-age creep of 3D printed segments with the consideration of stress history. The integral creep strain evaluation formula is first expressed in a summation form using superposition principle. The experimentally derived creep compliance surface is then employed to calculate the creep strain in the lattice model with a combination of stored stress history. These strains are then converted into element forces and applied to the analyzed object. The entire numerical analysis consists of a sequence of linear analyses, and the viscosity is modelled using imposed local forces. The model is based on the incremental algorithm and one of the main advantages is the straightforward implementation of stress history consideration. The creep test with incremental compressive loading is utilized to validate this model. The modelling results are in good agreement with experimental data, demonstrating the feasibility of the lattice model in early-age creep analysis under incremental compressive loading. To understand the impact of early-age creep on structural viscoelastic deformation during the printing process, additional analyses of a printed segment are carried out. These simulation results highlight the need to consider creep for accurate prediction of viscoelastic deformation during the printing process.

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. [ABSTRACT FROM AUTHOR]

In Singapore, there is an increasing need for independence from manpower within the Building and Construction (B&C) Industry. Prefabricated Prefinished Volumetric Construction (PPVC) production is mainly driven by benefits in environmental pollution reduction, improved productivity, quality control, and customizability. However, overall cost savings have been counterbalanced by new cost drivers like modular precast moulds, transportation, hoisting, manufacturing & holding yards, and supervision costs. The highly modular requirements for PPVC places additive manufacturing in an advantageous position, due to its high customizability, low volume manufacturing capabilities for a faster manufacturing response time, faster production changeovers, and lower inventory requirements. However, C3DP has only just begun to move away from its early-stage development, where there is a need to closely evaluate the process parameters across buildability, extrudability, and pumpability aspects. As many parameters have been identified as having considerable influence on C3DP processes, monitoring systems for feedback applications seem to be an inevitable step forward to automation in construction. This paper has presented a broad analysis of the challenges posed to C3DP and feedback systems, stressing the admission of process parameters to correct multiple modes of failure. [ABSTRACT FROM AUTHOR]

3D concrete printing is an avant-garde building process with the potential to revolutionise the construction industry by automating construction procedures, reducing material consumption, lowering form-work costs, and optimising structural elements. The current study proposes a methodology for developing plain and fibered 3D printable concrete mixes using locally available binders (cement, silica fume, fly ash, and limestone powder), fine aggregate, water, admixtures, polypropylene fibers, and steel fibers. The study presents the results of 24 trials conducted to develop mixes for concrete 3D printing. According to the present studies, the recommended flow for the mix to be extrudable, printable, and buildable is between 19–21 cm and the open time is 45–60 min. The printed specimens under bending failed monolithically with a single dominant crack. The plain and fibered 3D printed specimens possessed greater flexural strength than the in-situ cast specimens. The increase in flexure capacity is found to be in the range of 07–22%. [ABSTRACT FROM AUTHOR]

Concrete 3D Printing (3DP) is a potential technology for increasing automation and introducing digital fabrication in the construction industry. Concrete 3D Printing provides a significant advantage over conventional or precast methods, such as the prospects of topologically optimized designs and integrating functional components within the structural volume of the building components. Many previous studies have compiled state-of-art studies in design parameters, mix properties, robotic technologies, and reinforcement strategies in 3D printed elements. However, there is no literature review on using concrete 3D Printing technology to fabricate structural load-carrying elements and systems. As concrete 3DP is shifting towards a large-scale construction technology paradigm, it is essential to understand the current studies on structural members and focus on future studies to improve further. A systematic literature review process is adopted in this study, where relevant publications are searched and analyzed to answer a set of well-defined research questions. The review is structured by categorizing the publications based on issues/problems associated with structural members and the recent technology solutions developed. It gives an overall view of the studies, which is still in its nascent stage, and the areas which require future focus on 3D printing technology in large-scale construction projects.

The aim of this study is to question the need for alternative project delivery methods to foster the integration of concrete 3D printing in the construction industry. For this purpose, a literature review was carried out. The results indicate that the traditional planning and construction process will have to be reconsidered. On the one hand, new roles and changes in responsibilities may emerge, and, on the other hand, a holistic design process and early contractor involvement will be required to fully exploit the potential of concrete 3D printing. Therefore, alternative project delivery models need to be adopted.

Concrete 3D printing has the potential to reduce material and process waste in construction. Thus, it contributes to making the construction industry more sustainable through the use of digital-fabrication technologies. While concrete 3D printing is attractive due to its potential to realize complex designs, practical challenges include an increased chance of defects and deformities. Quality assessment of 3D-printed elements is essential for large-scale implementation. Workability of concrete is known to decrease with printing time and it impacts extrudability. It is usually visible in 3D-printed elements, with the lower layers having a smooth finish, while the top layers have cracks and discontinuities. A computer-vision-based quality assessment method is proposed in this paper using a two-bin Linear Binary Pattern textural analysis. Information entropy is used as the metric for measuring the texture variation within each layer and its changes over the layers are studied. A higher entropy value is found for layers having deformities. Finally, through the error-minimization technique, a threshold entropy value is calculated and, using this, the printed layers can be assessed and corrective actions taken. This paper contributes to developing a non-intrusive quality assessment technique for concrete 3D-printed elements. [ABSTRACT FROM AUTHOR]

The trending methodology in 3DCP is accompanied by extensive trial and error methods, leading to the final product's more expensive and time-consuming development. The specific printable combination of design, materials properties, and process parameters for successful 3D concrete printing (3DCP) process resembles a “secret recipe”. This study explores the design capabilities of numerical tools for 3DCP, understands its limitations and challenges, and provides an overview for future research direction. Different analytical and numerical models have been developed in the literature as a function of material properties, printing parameters, and the geometry of the final printed structures. These models serve to optimize the printing parameters and predict the performance of the printed product and rheological responses, hence, offering a safer and more economical solution. The analytical models provide the first-degree approximation and can be used for simple shapes such as straight or tilted walls; however, numerical methods are needed for more complex structures. The literature review shows an apparent delay in the progress of computational technology to catch the pace of interest of the construction industry in 3DCP. The prediction of 3DCP structure performance is not straightforward for complex geometries, variable process parameters, or multi-materials printing. Due to involving multi-physics phenomena at each sub process, the developed numerical models are limited to a specific sub-process range. The study presents a plan to integrate different sub-processes to build a single computational model from material mixing to final buildability.

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.

Estimating the early-age strength of 3D printed concrete is more challenging than that of conventional concrete due to the absence of formwork and increased variability in curing conditions. The common maturity method is ineffective for 3D printed structures since it fails to account for moisture content variations. This paper introduces a new approach using embedded sensors to continuously collect data on the electrical properties and temperature of 3D printed concrete, enabling accurate strength estimation under varying curing conditions. Empirical models based on electrical resistivity, internal temperature, and relative permittivity are developed and evaluated. The permittivity-based model can estimate the flexural strength of 3D printed specimens with at least 83% accuracy and a maximum root mean square error of 0.27 MPa under different curing conditions across three concrete grades. Additionally, an innovative curing technique involving the automated application of curing compounds is proposed and proven effective for 3D printed concrete. • An automated strength monitoring approach for 3D printed concrete is proposed. • The effect of different curing conditions on strength development is investigated. • The permittivity-based model is able to estimate the strength with high accuracy. • An automated curing system is proposed, tested, and proven effective. [ABSTRACT FROM AUTHOR]

With the increase of mining depth, the deep mine waterproof wall project faces the test of worse construction environment and higher risk of water damage. With the development of intelligent construction technology, it is necessary to introduce concrete 3D printing technology for the construction of coal mine waterproof walls, so as to adapt to more complex construction environment and engineering needs. Through uniaxial compression tests, the compressive properties of 3D printed concrete were tested under different printing methods and force directions. The results showed that the compressive strength of the 3D printed concrete was higher under the conditions of printing path B and loading along the direction parallel to the bonding layer. According to test results, the mine waterproof wall structure based on concrete 3D printing was designed. Then, ABAQUS was used to simulate the compressive strength and deformation of the 3D printed waterproof wall. The results showed that the ultimate load of the 3D printing module was 6.697e4kN and the deformation range was controllable, which meet the engineering requirements. The advantages of 3D printing mine waterproof walls are more flexible in design, faster in manufacturing, and more intelligent in operation. This work provides new ideas for the design and construction of waterproof walls in deep mines.

This article discusses the application of additive manufacturing (AM), also known as 3D printing, in the construction industry. The use of AM technologies in construction can reduce material waste, increase design flexibility, and contribute to resource efficiency. The article highlights various materials that have been tested for AM processes, such as concrete and rammed earth, and explores their potential for reducing environmental impact. The article also discusses the integration of computational design and digital fabrication methods in the construction process. Challenges and advancements in AM techniques, including data-driven models for quality control and the improvement of thermal insulation in AM-produced walls, are also addressed. The authors provide insights and recommendations for further research and development in this field. [Extracted from the article]

Additive manufacturing technologies are becoming more popular in various industries, including the construction industry. Currently, construction 3D printing is sufficiently well studied from an academic point of view, leading towards the transition from experimental to mass large-scale construction. Most questions arise about the applicability of construction 3D printers for printing entire buildings and structures. This paper provides an overview of the different types of construction 3D printing technologies currently in use, and their fundamental differences, as well as some significant data on the advantages of using these advanced technologies in construction. A description of the requirements for composite printing is also provided, with possible issues that may arise when switching from lab-scale construction printing to mass large-scale printing. All printers using additive manufacturing technologies for construction are divided into three types: robotic arm printers, portal-type printers, and gantry 3D printers. It is noted that gantry printers are more suitable for large-scale printing since some of their configurations have the ability to construct buildings that are practically unlimited in size. In addition, all printers are not capable of printing with concrete containing a coarse aggregate, which is a necessary requirement in terms of the strength and economic feasibility of 3D printing material for large-scale applications.

Additive manufacturing and in particular, concrete 3D printing has been suggested as one of the interesting solutions to unlock remote development, enhance the strength and capability of the local and national manufacturing and construction industries, and offer fast recovery in post-disaster scenarios. In this study, the remote housing construction challenges with a particular focus on Australian Northern Territory (NT) are reviewed and the feasibility and efficiency of using concrete 3D printing to tackle those challenges have been discussed. Besides the advantages of 3DP for remote housing, it's limitations and concerns have also been presented. Finally, some completed 3D-printed construction projects in remote locations were introduced. According to the findings of this review, to establish whether 3D printing is practicable and desirable in remote locations, trade-offs between several aspects, including materials, structural design, process efficiency, logistics, labour, and environmental impact, must be taken into consideration. In the case of using local materials that meet the printability, buildability and robustness requirements, 3DP could be considered a cost-effective solution for remote housing. However, researchers, designers, and decision-makers should consider the options, such as remote on-site fabrication, available local materials and their quality, and the large-scale manufacturing process and concrete 3DP limitations when evaluating the feasibility of using 3DP in comparison to conventional construction methods. [Display omitted] • Concrete 3D printing as a solution to overcome remote housing challenges has been investigated. • Advantageous and disadvantageous of concrete 3D printing for remote housing have been discussed. • Case studies on using 3D printing for remote applications have been reviewed. [ABSTRACT FROM AUTHOR]

This article presents the development and validation of a design-to-fabrication framework aiming to improve the efficiency of fabricating reinforced concrete building components for housing projects in the Kingdom of Saudi Arabia by incorporating 3D concrete printing technology. In particular, the research presents an algorithmic framework to mass customise a typical Saudi Arabian free standing house by utilising parametric modelling, topology optimization (TO), finite element analysis (FEA), and robotic 3D printing tools and techniques. The framework was validated by the fabrication of optimised reinforced concrete columns and by testing their structural performance under the Saudi Building Code (SBC 304). The findings demonstrate the benefits and drawbacks of the proposed framework and compare it to current Saudi conventional construction approaches. The paper also addresses the need for mass customisation in the construction industry of the Kingdom of Saudi Arabia • Design to fabrication of concrete building components. • Mass customisation of 3D-printing reinforced concrete frame structure. • Topology optimisation of 3D-printing reinforced concrete frame structure. • Validating structural performance of topology optimised column subjected to axial load. • Illustrating the efficiency of 3D printing optimised structural building components, mitigating labour and material waste. [ABSTRACT FROM AUTHOR]

Existing approaches from design to concrete 3D-printing fabrication can customize the shapes of compression-dominated concrete arches and vaults but has limited applications due to high facility requirements such as a robotic arm and a reconfigurable print bed for fabricating overhanging geometries. Therefore, there is a need to develop an alternative design-to-fabrication approach for 3D printers without such facility requirements. In this paper, concrete blocks were designed as prismatic shapes which could be customized by a most basic, gantry-based 3D printer with a flat print bed and could be assembled to a larger 3D arch structure designed based on stability and strength analyses. The feasibility of such approach was demonstrated by lab prototyping. Reduced facility requirements in this approach allow 3D-printing to be more widely applied for customizing compression-dominated structures. With further design method innovation in the future, this design-to-fabrication approach can be extended for compression-dominated structures with more complex geometries. • Concrete 3D-prinitng of compression-dominated structures with basic facility • Customized design 3D arch fabrication was proposed from 2.5D segments. • Incorporation of analyses at pre/post-assemble stage with design of modular arch • Compensating dimension offset in segment assembling reduces arch dimension errors. [ABSTRACT FROM AUTHOR]

This article presents a review of the current solutions for the rheological challenge of three-dimensional concrete printing (3DCP), providing a rheological definition for printability, and an overview of the current techniques for obtaining a printable concrete, placing special emphasis on understanding structural build-up and the current mixture proportions and admixtures used to improve it. A promising alternative for improving structural build-up is the use of entrained air (EA), as bubbles, whose effects are reviewed in generic yield stress fluids and then specifically in concrete. After revision of micromechanical models and experimental trials from literature on yield stress fluid bubble suspensions and concrete, EA appears to be ideal for 3DCP when generated by anionic surfactants, as it increases static yield stress and decreases plastic viscosity. Cationic surfactants, however, maintain or slightly decrease static yield stress. It is proposed that the lubricating or stiffening property of the bubbles determines their ability to deform under the shear stress generated by the surrounding fluid. The ability to deform depends on the surfactant used to entrain the bubbles and the mixture design of the concrete. Further experimental research must be carried out for the advantages of EA to be fully realized., Competing Interests: No competing financial interests exist., (Copyright 2022, Mary Ann Liebert, Inc., publishers.)

This paper provides a state-of-the-art report on the up-to-date research on the emerging 3D concrete printing technology from the concrete materials perspective. It reviews the recent research focused on understanding and characterizing the rheological necessities of the concrete printing process and discusses how the researchers are tailoring compatible mix proportions for the 3D concrete printing process by using eco-friendly binders, waste aggregates, chemical admixtures, and nano-additives. This paper systematically evaluates anisotropic behavior in the mechanical properties of printed concrete and establishes an order for anisotropic behavior in the compressive, flexural, and tensile strengths along three different axes (X, Y, and Z axes) of printed concrete. It evaluates the ratio of flexural strength to the compressive strength of printed concrete along the above three axes. This article explains the influence of variation of printing process parameters on the mechanical properties and discusses reinforcement approaches used for increasing structural performance. The microstructure at the interface of adjacent layers and also at the interface of the reinforcement-cement matrix is discussed. The recent research on the durability performance of printed concrete is critically discussed and future research needs for 3D concrete printing are identified in this paper. [ABSTRACT FROM AUTHOR]