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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 3D printing of concrete isa new kind of additive manufacturing technology, the iterative closest point method and oblique photogrammetry technology were used to examine the overall deviation, local boundary deviation, and arc angle radius of 3D printed components in order to accomplish the quick manufacturing of high-quality molded components using concrete 3D printing technology. The forming accuracy and buildability were examined in relation to the overall deviation and border deviation. Finally, the printing model was predicted using the border deviation and arc angle radius. The findings demonstrate that the highest forming accuracy of the component is achieved when the mix ratio for concrete 3D printing is cement: sand∶ fly ash∶ water reducing agent∶ coagulant∶ water = 1∶ 1. 12∶ 0. 09∶ 0. 004∶ 0. 006∶ 0. 32, the printing speed Vd is 45 mm / s, and the ideal extrusion speed Vj is 138 mm / s. The chromatogram is marked for its particular position deviation, and the oblique photography model is fitted, aligned, and aligned. It is clear that the concrete component created by 3D printing has a low constructability and significant compressive deformation at the fourth layer. By fitting the prediction model with the concrete 3D printing solid component, it can be seen that the error between the prediction model and the benchmark model is about 1 mm, which verifies the rationality of the proposed method and the prediction model. [ABSTRACT FROM AUTHOR]

This paper investigates the Near‐nozzle Mixing (NNM) technique for 3D printing cementitious mortar, focusing on achieving continuous and homogeneous material properties. The NNM's ability to print Natural Sand Mortar (NSM), Recycled Aggregate Mortar (RAM), and Lightweight Mortar (LWM) was assessed. Fresh and hardened properties of each mortar were examined, emphasizing standard deviation (STD) and coefficient of variation (CV) to measure material homogeneity. Fresh properties included slump flow, yield stress, air void volume, density, and water‐to‐cement ratio, while hardened properties covered compressive strength, flexural strength, hardened density, and thermal conductivity. Results showed low CV values for all mortar types, indicating high consistency and homogeneity. NNM showed is capability to print of various materials with customized properties. NSM showed the highest compressive strength, RAM balanced strength and sustainability, and LWM provided the best thermal insulation. The study highlights NNM's versatility and potential for construction applications requiring tailored properties, proving it a promising additive manufacturing solution. The research serves as a foundation for future studies on graded multi‐material printing. [ABSTRACT FROM AUTHOR]

Shotcrete 3D Printing (SC3DP) applies concrete layer by layer using a wet‐spray process. The resulting hardened concrete properties of the applied SC3DP layers (e.g. height, width or mechanical strength) are largely dependent on the selected material and process parameters. In this context, the nozzle geometry is an important influencing parameter. During printing, the velocity of the shotcrete jet is significantly influenced by the nozzle outlet diameter. Therefore, in the present study, the effect of the nozzle outlet diameter (15 ‐ 30 mm) is investigated with regard to the resulting layer homogeneity, i.e. local density and aggregate distribution in the cross‐section, and hardened concrete properties, i.e. flexural strength. By analysing the manufactured specimens, an uneven distribution of the aggregate is observed horizontally across the cross‐section of the layers. An accumulation of aggregate is present in the core of the layer resulting in a cement paste‐rich region in the edge areas. This leads to increased local densities in the core of the specimen. The application of the concrete with small nozzle outlet diameters results in the highest local densities and the highest flexural strength. [ABSTRACT FROM AUTHOR]

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.

In this work, we present a numerical model to analyse particle migration and its impact on local rheological properties when a high-yield stress suspension like 3D printable concrete is transported through a narrow circular pipe. The particle migration is studied through the lens of suspension rheology, where the effect of local particle concentration on rheological properties is accounted for using Krieger–Dougherty-type models. 3D printable mixtures with different aggregate-to-binder (a/b) ratios and flows at various discharge rates are evaluated. It is observed that, depending on the discharge rate and a/b ratio, the flow behaviour could deviate from that expected in a Poiseuille flow of Bingham fluid owing to shear-induced particle migration. Interestingly, as a consequence of particle migration, the formation of a local unsheared region close to the pipe wall is observed, apart from the plug zone at the pipe centre in the partially unsheared pipe flow of Bingham fluids. Often, for concrete pipe flow simulation, the particle size is not small enough to warrant local treatment since the finite size of the particle is not fully reflected in the flow domain. In this work, the developed numerical model is also extended to account for the finite particle size to study the transition between the sheared and unsheared regions and assess the effect of considering finite size in our simulation. Finally, the model's capability to predict global pressure loss in pipe flow is assessed through comparisons with experimental results. • A macroscopic continuum-based model is used to study particle migration. • Rheological parameters are treated as functions of the local particle concentration. • Model is used to simulate the pipe flow of different 3D printable concrete mixtures. • Non-local relation for particle pressure is used to reflect the size of aggregates. • A secondary unsheared region apart from the central plug zone is observed. [ABSTRACT FROM AUTHOR]

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.

Development of processes for the automated planning and production of individual reinforced concrete elements Industry 4.0, digitalisation and automation are the topics of high interest for research and development in the construction industry and related institutions these days. As a result, robots and robotic machines can be found more and more frequently in production halls. Following this trend, this paper presents research and development work currently being carried out by the Max Bögl Group and the Institute of Structural Engineering of the Universität der Bundeswehr in Munich. The first declared development goals of this collaboration concern the implementation of drivers of digitalisation and Industry 4.0 in the planning and production of precast reinforced concrete elements. For this purpose, in digital planning, a process for parametric 3D modeling and path planning for robotic applications is being developed. The resulting data sets are then used in the technical implementation using industrial robots for the individual production of reinforcement cages on the one hand and for the production of alternative component geometries using a concrete 3D printing process on the other hand. [ABSTRACT FROM AUTHOR]

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]

• W1.5 shows superior interlayer bonding and flexural strength. • Optimal stand-off distance is 13.5 mm to 15 mm. • Lattice beam achieved a failure load of 49.01 kN with flexural failure. This paper presents the optimal selection of cable reinforcement for concrete 3D-printed lattice beam. It also addresses key challenges associated with interlayer bonding and flexural strength of 3D printed elements. Three different types of reinforcement including 1.6 mm and 2 mm diameter rebar, (R1.6 & R2) and 1.5 mm wire (W1.5) with seven strings were evaluated with different stand-off distances of 10–20 mm. The interlayer bonding and flexural strength were investigated to determine the most effective reinforcement configuration. Results show that W1.5 reinforcement exhibited higher interlayer bonding and flexural strength as compared with R1.6 and R2. Subsequently, the optimal reinforcement configuration (W1.5) was embedded in a concrete 3D-printed lattice beam. The lattice beam was structurally evaluated using four-point testing, demonstrating an ultimate load-carrying capacity of 49.01 kN with a mid-span displacement of 2.99 mm. Moreover, it exhibited flexural failure with no premature failures such as inter-layer delamination. [ABSTRACT FROM AUTHOR]

• The dummy layer reduces geometry deviations and maximizes interlayer bonding. • The dummy layers significantly enhance the interlayer bonding of the top layer. • After introducing a dummy layer, geometrical deviation notably reduces. This paper presents the effect of dummy layers in concrete 3D printing to enhance interlayer bonding and reduce geometrical deviations. The specimens were printed by varying numbers of dummy layers at different layer heights using the optimized printing parameters. The impact of dummy layers on interlayer bonding was determined using a split tensile test and the geometrical deviations were analyzed using a 3D-scanning technique. Results demonstrate that significant improvement was found in interlayer bonding, notably at the top layer. For instance, by adding two dummy layers in specimen H10D2, the difference between the top and middle layers bond strength was reduced from 42.57% (i.e., for specimen H10D0) to 0.79%. Moreover, the dummy layers effectively minimized the geometrical deviations by achieving the desired layer dimensions in the top layer of specimens. [ABSTRACT FROM AUTHOR]

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.

Concrete 3D printing is an application of 3D printing technology for the construction of concrete structural and non-structural elements. It is a rapid method of construction without the use of formwork, with minimum labor involvement and reduced material wastage. Curved walls and complex structures can be constructed by modifying the print path and controlling the rheological properties of concrete. The fusion of this technology with waste materials is necessary to reduce the problems associated with the recycling of wastes and to minimize CO 2 emissions associated with the production of cement. In this study, two different municipal solid waste (MSW) incineration ashes (fly ash and bottom ash) were used to develop a concrete having rheological and hardened requirements of concrete used in 3D printing. Waste incinerator ashes were added as a substitute of ordinary Portland cement in concrete mix proportions. Flow table test and Gilmore needle test were used to measure the flow and setting time of concrete, respectively. Yield stress was measured by shear vane test. The buildability of ash containing printable concrete was simulated by comparing the vertical stresses due to the printing of concrete layers with the increase in the strength of the first stacked layer. Workability, open time, and buildability of the mix proportions were related to yield stress. The effect of adding waste incinerator ash upon the compressive strength was measured. The bond strength between layers at different printing time gaps was evaluated using bi-surface direct shear test. Experimental results showed that setting time promoting effect and initial yield stress enhancement by incinerated fly ash allows for a rapid construction speed with concrete 3D printing. This study concludes that incinerated fly ash can be successfully recycled in 3D printable concrete due to its favorable effects on rheology which are favorable for printing concrete. [ABSTRACT FROM AUTHOR]

Hybrid alkali cement (HAC) is regarded as a sustainable alternative to cementitious materials due to the use of more than 70 % of supplementary cementitious materials while the issues associated with geopolymers are avoided to a great extent. This paper proposes a new method of delivering HAC-based mixtures by a two-part printhead mixing process suited for 3D concrete printing (3DCP). The two-part mixing process addresses the conflicting rheological requirements in 3DCP by facilitating the rapid early-age strength development after placement while showing excellent pumpability prior to the extrusion. The proposed approach is based on introducing the Portland cement in a secondary mixing process to partially replace the fly ash or slag in the printable geopolymer mix. A series of experiments assessing the printability of fresh concrete following the two-part mixing process and the properties of hardened concrete were assessed. The results demonstrate that the replacement of FA with Portland cement (HAC-FA) yielded a more pronounced enhancement than slag-replaced mixes (HAC-S) with the increase in static yield stress (SYS) and modulus of elasticity by 17 times and 3.5 times respectively at 30 min, compared to the control mix. The hardened properties of printable mixes, namely compressive strength and interlayer bond strength at 28 days, revealed an enhancement for the HAC-25FA mix by 20 % and 64 %, respectively, again in comparison to the control mix. The apparent volume of permeable voids (AVPV) and microstructural analysis validated the hardened concrete properties, where the HAC-FA mixes showed the densest microstructure with a reduced apparent porosity, compared to other mixes. • HAC is studied as a sustainable alternative to Portland cement in concrete 3D printing. • A two-part print head mixing technology is proposed to meet the conflicting rheological requirements for 3D printing. • The static yield stress and elastic modulus of fresh printed concrete increased by 17 times and 3.5 times respectively. • HAC mixes showed dense and compacted microstructure. [ABSTRACT FROM AUTHOR]

Among the several geometry and process-related characteristics that determine the ultimate product quality of 3D printed concrete, one that has gained considerable importance is the height/thickness of the individual layers. Layer height dictates the number of interlayer interfaces, and influences the properties of the layer and the interfaces (both interlayer and inter-filament), for a given mixture and printer characteristics. This paper examines the influence of layer height on the constitutive response and failure of 3D printed concrete specimens under compression, investigated along the direction of layer build-up (or perpendicular to the layer interfaces), which is the dominant plane of loading in 3D printed walls and columns. Plain and steel fiber-reinforced wall elements with two different layer heights (7.5 mm and 15 mm) are printed, from which cylindrical and prismatic specimens are extracted and tested. The uniaxial compressive strength is seen to decrease with increasing layer height. The constitutive relationships of the specimens with different layer heights, along with volumetric strains, enable the extraction of crack initiation stress and unstable crack propagation stress, which are influenced by layer height and the presence of fiber reinforcement. The unstable crack propagation stress is lower than the peak stress, and it decreases with increasing layer height. Digital image correlation (DIC) is used to demonstrate the dominant effect of inter-filament interfaces on the crack propagation response and resultant failure. • Examination of the influence of layer heights on compressive response. • Dependence of critical stress states on layer heights. • Dominant effect of inter-filament interfaces on crack propagation. • Accounting for layer heights in conjunction with material design for better performance. [ABSTRACT FROM AUTHOR]

This study investigates the print head activation of an encapsulated additive to attain on-demand setting in 3D concrete printing for buildability enhancement. Sodium hydroxide (NaOH) is considered as a set accelerating additive, and it is encapsulated using a phase change material (PCM). The encapsulated NaOH is added during the initial mixing stage and the mix is heated at the print head to release the NaOH, which subsequently reacts with cementitious materials to attain the on-demand setting of the printed layer. The dosage of NaOH was varied from 0 to 5 wt% of the cement to determine the optimum dosage for buildability enhancement. The results showed that the static yield strength of the printable concrete after the print head activation increased with the NaOH dosage, however, this has resulted in reducing the compressive strength of the mixes. The fresh and hardened properties of the mixes with encapsulated NaOH were compared with the mix with nano-clay to assess two buildability enhancement approaches (set-on-demand vs traditional). It was found that the buildability enhancement using nano-clay was limited by pumpability constraints, whereas the activation of encapsulated NaOH was limited by compressive strength reductions. [ABSTRACT FROM AUTHOR]

The control of mortar rheology is of paramount importance in 3D printing concrete by extrusion. This is particularly sensitive for two-component (2K) processes that use an accelerator to switch the printed mortar very quickly from a liquid behavior to a sufficiently solid behavior to be able to be printed (i.e. structuration). After some main key points about measuring the structuration of printed mortars, we propose an original and simple inline test using a pocket shear vane tester. The test is able to measure over several decades of yield stress range, mobilizes small quantities of mortar and enables in-situ measurements on freshly printed layers. The results highlight the difference of structuration between a benchtop-prepared printable material and a truly printed material, fostering the importance of inline measurements, and demonstrating the quality of the method. This pocket shear vane test appears as good contender for a light and affordable rheometer for 2K printable mortars. • A 3DCP inline pocket vane test that suits fast structuration (100 Pa/s) is proposed. • A linear model fits early structuration of mortars accelerated by aluminum sulfate. • Potential of 2K strategies in adjusting structuration on the fly is demonstrated. • Inline and laboratory measurements differ : Inline testing is a necessity. • A methodology to choose and qualify 3DCP structuration tests is proposed. [ABSTRACT FROM AUTHOR]

• Interaction between inter-filament void, bonding, & geometric deviation is studied. • Investigated the influence of different printing parameters using RSM. • High speed & low extrusion with 1/8N d overlapping are optimal printing parameters. This study presents the effect of different printing parameters including printing speed, extrusion rate, and inter-filament overlapping distance on inter-filament bonding, inter-filament voids, and geometrical deviation in concrete 3D printed structures using Response Surface Methodology. Moreover, this study adopts a central composite design to generate a set of experimental runs and develop a second-order polynomial equation to quantify the effect of printing parameters. Results show that high inter-filament bonding with minimal inter-filament void and geometrical deviation can be achieved at high printing speed and low extrusion rate with 1/8N d (2.5 mm) inter-filament overlapping distance. [ABSTRACT FROM AUTHOR]

Extrusion-based concrete 3D printing is being increasingly used in the construction industry. This paper gives insights into the porosity and pore structure of 3D printed concrete elements using mercury intrusion porosimetry, and X-ray micro-computed tomography. The experiments were conducted with two different cement systems; among which a Portland cement-blast furnace slag blend and a calcium sulfoaluminate cement-limestone blended system. The study reveals that the interlayer region contains larger and interconnected pores with low tortuosity, which could lead to enhanced transport of ions. Using the MIP data, surface fractal dimension and tortuosity parameters were computed. It was observed that the calcium sulfo aluminate-limestone blended system has higher pore complexity and tortuosity than the Portland cement-blast furnace slag system. Compared to mercury intrusion porosimetry, the X-ray micro-computed tomography technique was able to characterize both open and closed pores present in the printed sample at the resolution of the scanning. A significantly higher open porosity and the presence of more elongated pores with a high aspect ratio were observed in the interlayer compared to the bulk region. The current study can be useful in understanding the transport of ions through different regions in printed elements to assess its durability performance. • Pore structure of 3D printed concrete was assessed using mercury intrusion porosimetry and X-ray micro-computed tomography • Tortuosity and multi-fractal dimensions were computed from the mercury intrusion porosimetry data. • Interlayer regions have larger and interconnected pores with low tortuosity, which could lead to enhanced transport of ions. • X-ray micro-computed tomography technique was able to characterize both open and closed pores present in the printed sample. • Interlayer regions have high open porosity and elongated pores with a high aspect ratio compared to the bulk region. [ABSTRACT FROM AUTHOR]