3D Printable Concrete Research Articles

A rheological model for concrete additive manufacturing

The advent of 3D construction printing has ushered in a revolutionary era, demanding deeper insights into the understanding of cementitious fluid materials. Despite notable progress in additive manufacturing technologies, traditional rheological models (i.e., Bingham Plastic and Herschel-Bulkley) due to asymptotic behaviors of its plastic viscosity term fall short in describing the fluid mechanical properties of 3D printable concrete. This poses substantial challenges to achieving precise control and consistency in its boundless possibilities of mix design formulation. In this paper, we introduce an original rheological model that broadly characterizes the physiomechanical behaviours of non-Newtonian fluids, with a primary emphasis on thixotropic 3D printable cementitious pastes. Contrary to conventional representations, it is successfully demonstrated and validated herein that flow characteristics of 3D printable concrete may be described by two distinct viscosity terms, both of which collectively defines an upper and lower bound apparent viscosity with respect to a proposed activation function.

Investigating the Interaction of Limestone Calcined Clay and OPC-Based Systems with a Methyl Hydroxyethyl Cellulose-Based Viscosity Modifier Used for 3D Printable Concrete

Investigating the Interaction of Limestone Calcined Clay and OPC-Based Systems with a Methyl Hydroxyethyl Cellulose-Based Viscosity Modifier Used for 3D Printable Concrete

Migration of particles suspended in yield stress fluids: Insights from numerical simulation of pipe flow of 3D printable concrete

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 Review on Development of 3D Printable Concrete by Utilizing Agro-Industrial Waste: Evaluation of Fresh Properties

A Review on Development of 3D Printable Concrete by Utilizing Agro-Industrial Waste: Evaluation of Fresh Properties

Thermal performance and life cycle analysis of 3D printed concrete wall building

Automated construction process with extrusion-based 3D concrete printing (3DCP) is widely recognised due to its ability to construct complex freeform geometrical shapes. Furthermore, the automation process reduces labour and minimises material wastage, thus improving productivity. The structural performance of printed structures has been widely discussed; however, addressing the knowledge gap in energy performance and their environmental impact needs further investigation. Thus, this study investigated and compared the insulation characteristics, life cycle cost and environmental impact assessment of 3DCP structures with traditional reinforced concrete members. The evaluation of the insulation properties of 3D printable concrete allows the characterisation of operational costs and greenhouse gas emissions incurred from the additional heating and cooling systems. Furthermore, this study also suggested a method to enhance the thermal resistance of 3DCP with recycled fibre recovered from face mask waste. A comparison between face mask fibre-reinforced 3D-printed wall element and conventional reinforced concrete wall is also performed across the thermal, life cycle cost and environmental impact parameters. The results showed that the insulation properties of 3DCP walls were increased by 49.5% with the addition of face mask fibres compared to RC walls. This results in reduced energy consumption from additional heating and cooling systems along with a reduction in greenhouse gas emissions, thereby improving the energy performance of the building. Further, face mask fibre-reinforced printed walls showed a reduction in the life cycle cost, mainly in the operation stage, due to the low labour requirement and elimination of formwork. Moreover, a significant reduction in the depletion of resources and ozone depletion was observed for 3DCP face mask fibre-reinforced walls, along with the reduced impact on human health and ecosystem damage. Consequently, the incorporation of face mask fibres into the 3DCP process paves the way for its potential in constructing energy-efficient and environmentally sustainable buildings.

Performance Requirements and Optimum Mix Proportion of High-Volume Fly Ash 3D Printable Concrete

In this study, a procedure for mixture design was proposed with the aim of meeting the requirements of extrudability, buildability, and shape stability in 3D printable concrete. Optimum water/binder ratio, sand/binder ratio, binder type, utilization ratio, aggregate particle distribution and quantity, and type and utilization ratio of chemical admixtures were determined for 3D printable concrete in terms of print quality and shape stability criteria. A total of 32 different mixtures were produced. It was determined that mixtures produced using a binder content with approximately 40% fly ash, a w/b ratio of 0.35, and aggregates with Dmax of 1 mm exhibit acceptable characteristics. Investigations were also conducted into the thixotropic behavior, rheological characteristics, and mechanical properties of the mixes that were deemed acceptable. As a result, it was determined that the increase in the amount of fly ash usage positively affected the buildability of the printed layers. Additionally, the dynamic yield stress ranging from 114 to 204 Pa, viscosity ranging from 22 to 43 Pa.s, and structural build-up value ranges suitable for the production of 3D printable concrete mixtures were determined.

Sustainable mix design for 3D printable concrete

Sustainable mix design for 3D printable concrete

Effect of sand gradations on the fresh properties of 3D printable concrete

Sand is frequently used as a fine aggregate in concrete mixtures, but the performance of concrete can be considerably impacted by regional variations in sand gradation. In this work, the effect of sand gradations on the fresh properties of three-dimensionally printable concrete (3DPC) mixtures was systematically investigated. The binder combinations (cement, fly ash, silica fume, limestone powder, ground granulated blast-furnace slag) and the water/binder ratio were kept constant throughout the trials. The sands used in the mixtures were standard Ennore sand (ES) (grades I, II and III) and locally available river sand (RS). The mini-slump heights and flow values of mixes made with RS and with optimal packing of binary and ternary combinations of the standard ESs were evaluated and compared with those of the unary packing of ESs and RS. A correlation between the fineness modulus of different sand gradations and printable flow time was determined. The influence of sand gradations and fineness modulus on buildability, shape retention, open time and extrudability were evaluated. It was found that the performance of the fresh 3DPC was influenced by the aggregate's gradation and grain size in addition to its fineness. In conclusion, different fine aggregate specifications must be chosen depending on the various 3D printing building conditions and design requirements.

Numerical simulation of three dimensional concrete printing based on a unified fluid and solid mechanics formulation

Deformation control constitutes one of the main technological challenges in three dimensional (3D) concrete printing, and it presents a challenge that must be addressed to achieve a precise and reliable construction process. Model-based information of the expected deformations and stresses is required to optimize the construction process in association with the specific properties of the concrete mix. In this work, a novel thermodynamically consistent finite strain constitutive model for fresh and early-age 3D-printable concrete is proposed. The model is then used to simulate the 3D concrete printing process to assess layer shapes, deformations, forces acting on substrate layers and prognoses of possible structural collapse during the layer-by-layer buildup. The constitutive formulation is based on a multiplicative split of the deformation gradient into elastic, aging and viscoplastic parts, in combination with a hyperelastic potential and considering evolving material properties to account for structural buildup or aging. One advantage of this model is the stress-update-scheme, which is similar to that of small strain plasticity and therefore enables an efficient integration with existing material routines. The constitutive model uses the particle finite element method, which serves as the simulation framework, allowing for modeling of the evolving free surfaces during the extrusion process. Computational analyses of three printed layers are used to create deformation plots, which can then be used to control the deformations during 3D concrete printing. This study offers further investigations, on the structural level, focusing on the potential structural collapse of a 3D printed concrete wall. The capability of the proposed model to simulate 3D concrete printing processes across the scales—from a few printed layers to the scale of the whole printed structure—in a unified fashion with one constitutive formulation, is demonstrated.

Bond-slip behaviour of textile-reinforcement in 3D printed concrete

Integration of reinforcement in extrusion-based 3D concrete printing (3DCP) is one of the significant challenges that limit its structural application. Providing textile reinforcement having high tensile strength, easy formability and non-corrosive nature as a potential reinforcement for 3DCP members enhances their structural performance. However, the bond between the printed concrete and the textile reinforcement is an essential factor that affects the composite action. This study investigates the bond-slip behaviour of three types of textile reinforcements (i.e., AR-glass, basalt and carbon) in high-performance 3D printable concrete. The bond characteristics were evaluated using pull-out load test specimens. The effect of rheological properties like viscosity and yield strength on the bond behaviour was evaluated by varying the cement content with two different replacement dosages of fly ash and slag. The modification of the nozzle to incorporate textile reinforcement as an in-process reinforcement method for 3DCP is also discussed. Test results showed that the addition of fly ash reduced the viscosity and yield strength, thereby enhancing the bond strength and pull-out load. However, reduced viscosity and yield strength resulted in poor buildability. When compared to the control mix, the mix with 15% slag replacement showed 40% increased bond strength with good buildability and easy pumping. The modified nozzle incorporates the textile reinforcement during printing, and scanning electron microscopy images show that the printable concrete was observed to bond well with the multifilament yarns of the textile. Furthermore, analytical modelling was conducted to predict the pull-out load versus slip behaviour, and a comparison of the predicted and experimental behaviour is presented.

Effect of Silica Fume Utilization on Structural Build-Up, Mechanical and Dimensional Stability Performance of Fiber-Reinforced 3D Printable Concrete.

It is known that 3D printable concrete mixtures can be costly because they contain high dosages of binder and that the drying-shrinkage performance may be adversely affected. Mineral additives and fibers are generally used to control these negative aspects. In this study, the use of silica fume, a natural viscosity modifying admixture, was investigated to improve the rheological and thixotropic behavior of 3D printable concrete mixtures reinforced with polypropylene fiber (FR-3DPC). The effect of increasing the silica fume utilization ratio in FR-3DPC on the compressive strength (CS), flexural strength (FS), and drying-shrinkage (DS) performance of the mixtures was also examined. A total of five FR-3DPC mixtures were produced using silica fume at the rate of 3, 6, 9, and 12% of the cement weight, in addition to the control mixture without silica fume. As a result of the tests, the dynamic yield stress value decreased with the addition of 3% silica fume to the control mixture. However, it was found that the dynamic yield stress and apparent viscosity values of the mixtures increased with the addition of 6, 9, and 12% silica fume. With the increase in the use of silica fume, the CS values of the mixtures were generally affected positively, while the FS and DS behavior were affected negatively.

Mixing approach for 3D printable concrete: method of optimisation of superplasticiser dosage

This study is a systematic investigation of superplasticiser (SP) addition methods and optimum SP dosage with various water-to-binder ratios (w/b) for mixing three-dimensional printable concrete. In this study, five distinct strategies were adopted to arrive at the optimum method of addition. In the first strategy, a random mixing approach was applied to identify, through visual observation, methods for adding SP with varying time patterns. Secondly, a constant time pattern was adopted from the random approach for mixing and the optimal SP dosage was determined. In the third strategy, different methods of adding the optimum SP dosage were examined. In the fourth strategy, the batching effect of the material with the optimum SP dosage was assessed. Finally, the printable regions with different values of w/b and SP dosages were correlated. It was observed that the optimum SP dosage, in the range of 0.10–0.21% of binder, with w/b = 0.21–0.25 achieved adequate printability parameters by full addition of SP following a constant wet mixing time as the optimal application. However, after applying the optimum SP dosage, a supplemental SP dosage is required at appropriate intervals to retain the workability for higher batches.

A theoretical model to predict the structural buildability of 3D printable concrete

A theoretical model to predict the structural buildability of 3D printable concrete

The Physicomechanical Behavior and Microstructure of Air-Entrained 3D Printable Concrete

The Physicomechanical Behavior and Microstructure of Air-Entrained 3D Printable Concrete

Investigating the impact of coarse aggregate dosage on the mechanical performance of 3D printable concrete

Investigating the impact of coarse aggregate dosage on the mechanical performance of 3D printable concrete

Comparison of the Effect of Nano Cellulosic Additives on Rheological Parameters for 3D Printable Concretes

In 3D printable concretes, fresh requirements such as pumpability, workability, constructability are affected by the rheological properties of the mixture. High yield stress and high viscosity cause blockages in the transmission line, while low yield stress and low viscosity cause the mixture to not provide the required shape stability. Even if the mixture to be printed has suitable rheological parameters, it is very important in terms of workability that it can be preserved over time. Here, cellulose nanocrystals and cellulose nanofibers were used in cement paste mixtures in order to ensure sufficient workability time in 3D printable concrete mixtures, and also to ensure that the originally designed rheological properties can be maintained over time. The Bingham model, which was created as a result of the measurements made with the viscometer device, was used to evaluate the rheological parameters of the mixes containing cellulose nanocrystal and cellulose nanofiber additions in varied amounts. As a result of the study, it was determined that the yield stress of the reference sample increased by 290% 45 minutes after the preparation of the mixture, while this rate decreased to 135% in the use of cellulose nanocrystals and to 79% in the use of cellulose nanofibers. While it increased by 205% at the end, this rate decreased to 37% with cellulose nanofibers and to 68% with cellulose nanocrystals. When the different additives are compared, it was concluded that cellulose nanofiber may be more effective than cellulose nanocrystal in controlling the increase in viscosity and yield stress over time.

Experimental Investigation on Thermal Insulation of Sustainable 3D Printable Concrete by Using Corncob Powder

The construction industry is witnessing the latest technology advancement in the form of 3D printing, which promises to revolutionize the sector by reducing costs, material wastage, and environmental impact. One significant approach to achieving these goals is through the incorporation of various supplementary cementitious materials. This research work aims to study the utilization of corn cob powder (organic waste from agricultural industries) as a thermal insulation material in conjunction with other cement supplementary materials (fly ash, and silica fume). The study focuses on evaluating the material’s rheological properties, such as slump, initial and final setting times, and flowability. Furthermore, the investigation extends to analyzing the hardened properties of the concrete, including compressive strength, split tensile strength, and flexural strength under varying temperature conditions. Results shown that the compressive, split tensile and flexural strength was increased up 5 % to 7% with the inclusion of corn cob powder at 5% and it exhibits good resistance to high temperatures.

Image‐based analysis of fresh concrete flow ‐ determining the correlation between flow behavior and rheological properties

AbstractBesides compressive strength, the workability of fresh concrete is one of the most important characteristics of concrete. Only by adapting the rheology of the fresh concrete to the geometry of the element to be casted, the formation of air voids and damages can be avoided. This holds even more so true for 3D printable concrete. Currently, empirical test methods such as the slump test are used to determine rheological parameters. Rheometer tests, on the other hand, allow a much deeper insight into the rheological properties of concrete but are more challenging. Further, all currently available test methods can only be applied on a batch basis.In the paper at hand, a new approach for an automatic digital concrete quality control is presented using modern computer‐vision based analysis methods. Using a newly developed experimental setup, the flow of mortar down an inclined open channel is studied using a monocular camera setup. Differences in the mortar's rheology result in different flow behaviors which can be optically detected. Utilizing dense optical flow, rheological parameters are determined from the acquired monocular image sequences. The results shown in this paper prove that the computed flow behavior of the investigated mortars precisely correlates with their rheological properties, demonstrating the high potential of the method for an automated in‐line testing of fresh concrete e.g. during the discharge of a mixing truck.

Mix design, optimisation and performance evaluation of three-dimensional printable concrete

Three-dimensional (3D) concrete printing (3DCP) is a cutting-edge construction method that has recently received much attention. Most 3DCP research studies have focused on printer development, printable material mix designs and the complexity of geometry shapes. This research study primarily focused on determining appropriate mix proportions and suitable 3D-printable concrete (3DPC) mix designs using a trial-and-error approach. Experimental tests were carried out on 27 trial mixes made with different materials to determine printable properties such as flowability, buildability, extrudability and open time. Printed and cast samples were tested for compressive strength. The 3DPC mix with 19% ordinary Portland cement, 23% fly ash, 7% silica fume, 13% ground granulated blast-furnace slag, 4% limestone and 0.22% superplasticiser (% by mass of total binder) was found to be an ideal mix proportion, exhibiting the required 3DPC characteristics such as good buildability, easy extrusion, low setting time, mix cohesiveness and reduced deformation. The proposed mixing protocol and the suggested 3DPC mix design are encouraging for large-scale 3DCP. To demonstrate the application of the 3DPC mix, 3D-printed concrete furniture was fabricated with a nozzle of size 30 mm, an extrusion speed of 100 mm/s and a printing speed of 60 mm/s.

Influence of rheology on mixing homogeneity and mechanical behavior of twin-pipe 3D printable concrete

The twin-pipe pumping technology has been developed for the stiffening control of 3D printable concrete, which is achieved by pumping two different mixtures separately and blending these mixtures using a static mixer before extrusion. The combination of the two mixtures undergoes a significant phase transition in the static mixer from liquid to solid due to accelerated hydration. The phase transition, as well as the mechanical performance of hardened elements, is strongly influenced by the mixing homogeneity of the mixtures. In this study, we examine how the rheological behavior of the two mixtures being combined in the static mixer affects the mixing homogeneity. The rheological behavior was studied by performing flow curve measurements using a dynamic shear rheometer. To characterize the mixing homogeneity, polished cross-sections of 3D-printed elements were prepared and characterized using an innovative macropixel-based image analysis procedure. Specifically, the image analysis-based procedure involves identifying the two mixtures by applying color segmentation, followed by the Poole index method to assess the mixing homogeneity. The results indicate that a low yield stress, especially for the main constituent mixture of which the flow rate is higher than the second constituent mixture, is advantageous to achieve a higher mixing homogeneity. The viscosity or the viscosity ratio of the two constituent mixtures is found to have a minor influence on the mixing homogeneity.