Printable Concrete Research Articles

Assessing 3D-printed concrete process parameters through Discrete Element Modeling

Three-dimensional concrete printing (3DCP) has emerged as a promising manufacturing technique in the civil engineering sector, offering myriad advantages over traditional construction methods. Despite its potential, challenges persist in optimizing the manufacturing stage of 3DCP, including determining optimal fresh concrete rheology, layer thickness, print path, and nozzle characteristics. In this study, we incorporate the Discrete Fresh Concrete model (DFC) into our Discrete Element Method (DEM) code to simulate the rheological behavior of fresh printable concrete during printing, aiming to explore a comprehensive range of process parameters and their combinations to enhance understanding and optimization 3DCP process. Through a series of simulations, we systematically vary some of the process variables such as concrete mix design, nozzle specifications, and printing speed to investigate their influence on the printed output quality. By the obtained results, we aim to identify the key parameters that significantly affect the process, offering insights for refining 3DCP technologies and helping guide their development. We believe methodologies of the type as shown here may be an efficient tool for advancing 3DCP technologies.

Biochar-augmented climate-positive 3D printable concrete

Three-dimensional (3D) concrete printing is a revolutionary technology in the construction industry. Here we show that climate-positive biochar is a carbon-negative additive for decreasing the carbon footprint of 3D printable concrete, while enhancing its performance. As biochar enhanced the effective water-to-binder ratio and served as a substrate for hydrates, the polymerization of hydrates increased in biochar-augmented concrete. The incorporation of 2 wt% biochar enhanced the structural build-up rate of fresh mixtures by 22% at 40 min. The 3D printing tests demonstrated that biochar improved the pumpability and extrudability of mixtures at the initial 20 min, and enhanced the buildability of 3D printed concretes at the after 40 min. The carbon footprint of 3D printable concrete was reduced by 8.3% through incorporating 2 wt% biochar. Thus, we developed a desirable biochar-augmented mixture for 3D concrete printing. Future field-scale application will make substantial contribution to the attainment of carbon emission reduction.

Effect of hydroxypropyl methylcellulose and aggregate volume on fresh and hardened properties of 3D printable concrete

Three-dimensional (3D) concrete printing necessitates a balance between various ingredients of the mix composition. This study investigated the effect of hydroxypropyl methylcellulose (HPMC) dosage at various aggregate volumes on fresh, rheological, and mechanical properties of 3D printable concrete (3DPC). Accordingly, 3DPC mixtures having three aggregate volumes, namely 44, 41, and 38 %, were produced at a constant water-to-binder ratio. For each aggregate volume, three HPMC dosages, namely 0, 0.14, and 0.28 % by weight of cement, were studied. A mini-slump flow table and a manual printing gun were used to assess the flow diameter and printability. Rheological properties were determined using a rotational rheometer and extrusion device. The buildability was assessed through green strength testing. Results showed a directly proportional relationship between HPMC dosage and fresh and rheological properties of these mixtures. At a constant w/c ratio, increasing the aggregate volume led to higher green strength and extrusion pressure at all piston-moving velocities. Overall, at an early age, the effect of HPMC dosage was more significant on the static yield stress of mixtures with lower paste volume while being more accentuated on the green strength for mixes with higher paste volume. The positive impact of increasing HPMC dosage on the green strength becomes insignificant at later ages. The effect of increasing HPMC dosage, however, was more pronounced on the extrudability of mixtures with higher paste volume by preserving their extrudability at later ages. Finally, HPMC addition led to strength losses of up to 28.63 and 32.7 % for flexural and compressive strength, respectively.

Investigation of fresh and hardened properties of 3D printable concrete containing ozone-modified carbon fiber

In this study, the effect of using carbon fiber surface modified with ozone on the fresh-hardened state properties, high temperature resistance and rheological properties of 3D printable concrete (3DPC) was investigated. A total of 7 different 3DPC were prepared by adding modified and unmodified carbon fibers to the mixture at different ratios. Fiber surface modification was characterized by XPS analysis. The modification process improves the fiber/matrix adherence of 3DPC mixtures, resulting in an increase in compressive strength. The flexural strength of the mixtures increases with fiber modification, regardless of the fiber utilization ratio. Dynamic yield stress and apparent viscosity values of the mixtures decreased with the increase in fiber utilization ratio. τ3.p/τ2.p and Athix methods are more suitable for comparing the thixotropic properties of 3DPC mixtures with modified fibers suitable for comparing the thixotropic properties of 3DPC mixtures with modified fibers.

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.

Snapshot on 3D printing with alternative binders and materials: Earth, geopolymers, gypsum and low carbon concrete

The rapid development of 3D concrete printing now offers mechanical efficiency and freedom to push the limits of construction design. The digital manufacturing process holds potential for reducing carbon footprints through design optimization. Printable concrete, which is a mix of cement (based on ordinary Portland cement), aggregates, and admixtures, is attractive due to widespread and cost-effective constituents. However, many common formulations omit gravel, requiring higher cement paste volumes and inducing significant embodied carbon. Assessing the potential of low-carbon cements like Limestone Calcined Clay Cement (LC3), calcium aluminate cement (CAC), or magnesium-based cement for 3D printing is a current challenge that can address this issue. Tailoring these construction materials to printing applications and environmental needs now drives scientific exploration. This paper comprehensively reviews alternative materials and binders such as earthen materials, geopolymers, low carbon binders or gypsum-based materials, addressing fresh and hardened properties, developed digital processes, targeted applications, and discussing advantages and drawbacks of each alternative.

Test Procedures and Mechanical Properties of Three-Dimensional Printable Concrete Enclosing Different Mix Proportions: A Review and Bibliometric Analysis

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

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.

Geometric quality evaluation of three-dimensional printable concrete using computational fluid dynamics

Geometric quality evaluation of three-dimensional printable concrete using computational fluid dynamics

Mechanical performance and permeability of low-carbon printable concrete

Common issues in 3D printed concrete arise due to its high cement content, processing requirements, and the lack of extensive research into its long-term performance. To this end, this study explores using supplementary cementitious materials from local regions to partially replace cement, aiming at reducing the carbon footprint. Various printable mixtures with different substitution rates are formulated, and corresponding mechanical and permeability tests are conducted. It is revealed that the compressive and flexural strengths of 3D printed concrete with low cement content were lower than the strength of cast concrete due to the construction process of printed concrete; the mechanical strength of 3D printed concrete showed prominent anisotropic characteristics. It was found that, compared with the other two sets of ratios, the higher contents of FA and GGBFS could effectively fill the pores of the printed concrete. Both the capillary water absorption and the content of chloride ions of the low-carbon mixture were significantly lower than that of the pure cement-printed specimens.

Three-Dimensional Printable Concrete by an Ultra-Thin Nozzle and Fully Sealed Extrusion

Three-Dimensional Printable Concrete by an Ultra-Thin Nozzle and Fully Sealed Extrusion

Encapsulation of sodium silicate to attain on demand buildability enhancement in concrete 3D printing

This study investigates the encapsulation of a buildability enhancing additive using a phase change material (PCM) as a thermo-responsive additive for concrete 3D printing. The encapsulated additive is mixed with printable mixes and activated at the print head. The printhead activation via the heating process dissolves the capsules and releases the buildability enhancing additive to attain the required rheological properties for printing. A sodium silicate-based set accelerator was used as the buildability enhancing additive and encapsulated using a paraffinic PCM. The comprehensive experimental study was conducted to understand the effect of encapsulated sodium silicate on the pumpability of concrete followed by buildability after print head heating. It was demonstrated that the smaller addition of encapsulated sodium silicate (5 %) followed by print head activation resulted in the static yield strength (SYS) of 122 kPa after 25 min of placement compared to 8 kPa observed for mixes containing nanoclay as a thixotropic additive. Furthermore, the dissolution process of sodium silicate was assessed via an analytical method using optical technology to determine the diffusion coefficient of sodium silicate in the printable concrete. The proposed method was validated by printing a thin vertical wall with the optimised mix design developed during the study. Consequently, the mechanical properties of the printed specimen were investigated. The mixes containing the encapsulated additive showed a compressive strength reduction by up to 47 % for mould cast and 3D printed specimens and this was correlated to increased porosity of the mixes.

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.

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.