Role of temperature in 3D printed geopolymers: Evaluating rheology and buildability

doi:10.1016/j.matlet.2021.129680

Materials Letters

Volume 293, 15 June 2021, 129680

https://doi.org/10.1016/j.matlet.2021.129680 Get rights and content

Highlights

•
Geopolymers do not meet the rheology required for pumping and 3D printing.
•
Fluid mixtures are easily pumped but cannot support the weight of the overlapping layers.
•
A systematic heating process can quickly transform fluid mixtures into buildable ones.

Abstract

The mix design of binders with fluidity for pumping and at the same time consistency for printing is one of the most challenging tasks to make 3D printing technology feasible for large-scale buildings. On one hand high-fluid mixtures are better for pumping but on the other hand these do not support the overlapping of layers. For 3D printing geopolymers, this problem can be overcome by manipulating temperature. This work demonstrates how high-fluid mixtures can be quickly turned into buildable ones, continuously, from pumping to printing with a systematic heating process. Insight from this work provides valuable information to easily set the rheology and buildability of 3D printed geopolymers.

Introduction

3D printing technology, generally referred as additive manufacturing, is well-consolidated in many industries but is still incipient for large-scale buildings [1], [2]. The usage of 3D printing in construction offers many advantages when compared to the traditional casting methods, including saving costs and time, and related to environmental aspects. Ecologically correct building processes can be easily introduced with the use of recycled raw materials, such as construction and industrial wastes, as well as minimize waste and dust generation compared to traditional methods. Attempts have been made to merge this technology with eco-friendly materials instead of traditional concretes. Geopolymers are considered the best alternative due to the great reduction of greenhouse gas emissions in their manufacturing process [3]. However, unlike traditional concretes, geopolymers do not meet the rheological requirements for use in the 3D printers as they are extremely sensitive to the water/solid ratio content, to the alkali-activators type, and to the mineral sources [4]. The lesser content of solids and activators, the greater the fluidity and workability, which makes pumping all the way to the printing nozzle easier. On the other hand, excessive fluidity impairs the ability to support the weight of overlapping filaments, i.e., the buildability [5].

The construction size and speed have also to be considered. Highest speeds and smaller construction sizes shorten the time gap between each printed filament, and inevitably a higher structuration rate, or buildability, is required to produce multifilaments [1]. Consequently, intensive efforts have been conducted to find printable mixtures with optimized rheological behavior combining low viscosity during pumping and high yield stress after printing. In the concretes case, this behavior can be achieved with superplasticizers and setting accelerators [1]. In the case of geopolymers, these admixtures are usually inefficient [6], [7] but improvements might be achieved with a heating device coupled to the printhead. Unlike concretes, the paste temperature can be used to effectively control the reaction rate of geopolymers and, consequently, its rheological properties during printing. In this sense, this work evaluates the role of temperature in different metakaolin-based (MK-based) formulations used in the 3D printed geopolymers from the rheological point of view.

Section snippets

Experimental

The metakaolin used was supplied by Metacaulim do Brasil Indústria e Comércio, Brazil, and it is composed by 54.2 SiO₂, 34.8 Al₂O₃, 3.6, K₂O, 2.2 Fe₂O₃, and 1.6 TiO₂ (wt%) with a loss on ignition of 3.0%. Its particle size is D_10;50;90 = 2.3; 12.9; 56.1 µm, respectively. Two alkali-activators were used: sodium silicate (from Quimidrol, Brazil) composed by 10.8 Na₂O, 34.2 SiO₂, and 55.0 H₂O (in wt%) and 10 M sodium hydroxide solution (Vhtex, Brazil) with 99.9% purity. From these materials, four

Results and discussion

Fig. 2(a) and (b) shows the yield stress evolution and the Vicat needle penetration depth obtained with the geopolymer tested pastes. In Fig. 2(a), the buildable zone where samples were able to be printed is highlighted as range between 350 and 800 Pa. The activators content, as well as the SiO₂/Al₂O₃ ratio and the water content defined the rheological properties of the 3D printed geopolymer pastes. Sample D showed the higher structuration rate and was the unique composition which required

Final considerations

The adequacy of rheology is one of the main challenges of 3D printing of binders. For 3DPG, the usage of temperature is the key to overcome this issue. This study demonstrated how a pre-heating process can be especially useful in 3D printing building projects by allowing to set the desired rheology of MK-based geopolymer pastes independent on the mixing ratio. This approach makes it possible to quickly turn highly-fluid and easily-pumpable admixtures into buildable ones during printing by using

CRediT authorship contribution statement

Marcelo Tramontin Souza: Conceptualization, Methodology, Validation, Data curation, Writing - original draft. Lisandro Simão: Conceptualization, Methodology, Validation, Data curation, Writing - review & editing. Elisângela Guzi de Moraes: Writing - review & editing. Luciano Senff: Writing - review & editing, Methodology. José Renato de Castro Pessôa: Writing - review & editing. Manuel J. Ribeiro: Writing - review & editing, Formal analysis. Antonio Pedro Novaes de Oliveira: Writing - review &

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the Coordination for the Improvement of Higher Education Personnel (CAPES), Project N°CAPES-PRINT/88881.310728/2018-01 and funded by the National Council for Scientific and Technological Development (CNPq). Lastly, Lisandro Simão thanks the Human Resources Program of the National Agency of Petroleum, Natural Gas and Biofuels (PRH-ANP) and Financier of Studies and Projects (FINEP) for supporting its work.

References (10)

M.T. Souza et al.
3D printed concrete for large-scale buildings: an overview of rheology, printing parameters, chemical admixtures, reinforcements, and economic and environmental prospects
J. Build. Eng.
(2020)
P.J.S. Cruz et al.
Additive manufacturing effect on the mechanical behaviour of architectural stoneware bricks
Constr. Build. Mater.
(2020)
L. Assi et al.
Sustainable concrete: building a greener future
J. Clean. Prod.
(2018)
L. Simão et al.
Development of new geopolymers based on stone cutting waste
Constr. Build. Mater.
(2020)
D.-W.W. Zhang et al.
The study of the structure rebuilding and yield stress of 3D printing geopolymer pastes
Constr. Build. Mater.
(2018)

There are more references available in the full text version of this article.

Cited by (23)

3D printed sustainable low-cost materials for construction of affordable social housing in Brazil: Potential, challenges, and research needs
2024, Journal of Building Engineering
3D Concrete Printing (3DCP) is presented as an important process in the future of civil engineering, as it accelerates the construction process, reduces labor costs, and potentially generates significantly less waste materials. Currently, 3DCP has been delayed as a technical solution for Latin American. However, it could be an important option for tackling the housing deficit in developing countries as well. The deployment of 3DCP depends on many different local factors, either political, economic, or technological. This paper discusses the potential, challenges, and research needs to deploy 3DCP in Brazil. It starts presenting the Brazilian economic context in the struggle to reduce the housing deficit over the years. Then, the challenges related to the implementation of 3DCP are compared with the opportunities, such as the abundance of low-carbon materials (earth-based, biomass, etc.), which could turn 3DCP into a sustainable business. Although this review is focused on Brazil, the authors believe that the context also applies to many other developing countries with similar social inequality conditions.
Effect of reactivity of different metakaolin mixtures on geopolymer extrudability
2024, Journal of Building Engineering
Additive manufacturing of geopolymers is an innovative technology for research and development This work highlights effect of different metakaolin of mixtures reactivity on geopolymer extrudability. Extrudability tests were carried out on geopolymer pastes from different metakaolin ternaries diagrams using two alkaline (potassium silicates K and sodium silicate KNa) solutions. Extrudable areas were delimited. To understand the differences, the reactivity of the different metakaolin mixtures was evaluated. The results showed that for the extrudable areas, the zeta potential values of the metakaolin mixtures ranged from −50 to −60 mV with K solution and were around −60 mV with the change of solution (KNa). Moreover, the extrudable area corresponds to an energy of oligomer formation (determined by thermal analysis) determined between 1.67 and 1.85 kJ mol⁻¹ with metakaolin ternary diagram M1-MI-M5 and 1.58 and 1.76 kJ mol⁻¹ for metakaolin ternary diagram M1-M2-M5. Whatever the alkaline solution used, the alkaline cation concentration of the extrudable domains is greater than or equal to 2.80 mol. L⁻¹. Mechanical strengths increase around 10 % from solution K to KNa. All these results are confirmed by using other aluminosilicate sources, such as argillite (clay calcined at 650 °C) and mixture of several clays (A650₃₀-M1₇₀ and A650₅₀-M1₅₀).
Alkali activated materials applied in 3D printing construction: A review
2024, Heliyon
This study aims to contribute to the promising field of alkali-activated materials (AAM) used in 3D printing for construction. Presented as a comprehensive review, the research provides valuable insights for researchers within and beyond the field. The study focuses on identifying prevalent research trends and accessing pertinent information on materials, methodologies, and parameters of interest. The study commenced with a bibliometric analysis of 55 carefully selected publications, followed by an in-depth review of these articles categorized into extrusion-based and powder-based systems. Emphasis was placed on the materials used, methodologies employed, and key findings from these studies. The bibliometric analysis unveiled prevalent keywords, their relevance in the field, highly cited articles, and collaborative networks among researchers. The most influential countries in terms of publications are Australia, China, and Singapore. The review highlighted commonly used materials and their potential impacts on large-scale applications of AAM, exploring how various precursors, activators, additives, aggregates, and reinforcements shape the properties of printed AAM, featuring innovative approaches with alternative materials. The methodologies employed in these studies and trends in characterization were outlined, due to the absence of standardized tests for materials in 3D printing applications. The study emphasized how material properties vary concerning production processes, printing parameters, curing methods, and post-treatment, outlining advancements in material characterization necessary for achieving a printable mix design. Through the analysis of these 55 articles, key scientific challenges and hurdles in large-scale applications were identified, suggesting potential focal points for further studies. In summary, AAMs exhibit substantial uniqueness and complexity due to their diverse material composition, resulting in varying properties in both fresh and hardened states. However, this diversity also signifies the adaptability of AAMs to diverse equipment, construction techniques, and desired specifications, showcasing their potential to revolutionize traditional construction by integrating technology and sustainability.
Slag-modified metakaolin-based 3D printed geopolymer: Mechanical characterisation, microstructural properties, and nitrogen physisorption pore analysis
2024, Journal of Building Engineering
This study aims to enhance metakaolin (MK)-based binders with slag up to 30% at 10% intervals and increase the aggregate-to-binder ratio (a/b) from 1.6 in a previous study to 2 for extrusion-based 3D printed geopolymer concrete (3DPGPC). Sodium phosphate (3% by mass of binders) was used to tailor the fresh properties of the slag-modified MK-based 3DPGPC mixtures to achieve sufficient open time for constructability. After 28 days of curing age, cylindrical 3DPGPC specimens cored perpendicular to the printing direction (D1) exhibit an average compressive strength of 23.7–31.52 MPa and the specimens cored parallel to the printing direction (D3) exhibit an average compressive strength of 25.25–33.13 MPa. Also, an increase in a/b from 1.6 to 2 increases the average compressive strength by 18% in D1 and 25% in D3. The average flexural strength of specimens in D1 attained 5.48–7.29 MPa, while the average interlayer bond strength of 3DPGPC beam specimens attained 5.40–6.90 MPa. An increase in a/b from 1.6 to 2 enhanced average flexural strength by 6%. Furthermore, the 28-day splitting tensile strength of cored cylindrical 3DPGPC specimens attained 1.79–2.16 MPa in D1 and 2.04–2.43 MPa in D3. Microstructural characterisation revealed the formation of C-S-H, N-A-S-H and C-A-S-H gel with increasing slag inclusion due to the presence of Ca²⁺ion. Nitrogen physisorption analysis shows that the adsorption and desorption isotherm curves and hysteresis loops were not altered but more nitrogen by volume was absorbed due to the formation of a significant quantity of C-S-H, N-A-S-H and C-A-S-H gel. The adsorption and desorption isotherms fall under the mesopores structure of 2–50 nm using the IUPAC technical report classification. The Brunauer-Emmett-Teller (BET) surface area increases by 67, 69, and 78% as slag content increases by 10, 20 and 30% due to the polymerisation of the reactive phases, which densify the matrices. The enhanced mechanical performance, microstructural properties, and pore structure system of slag-modified MK-based 3DPGPC ascertained that it is suitable for construction applications.
Effect of the superplasticizer addition time on the fresh properties of 3D printed limestone calcined clay cement (LC<sup>3</sup>) concrete
2023, Case Studies in Construction Materials
Although 3D concrete printing (3DCP) is considered one of the most significant innovations in the construction sector, its large cement consumption remains an environmental concern. In response, limestone calcined clay cements (LC³) have emerged as a promising alternative to Portland cement (PC) due to their potential for reducing environmental impact. While previous studies have shown the influence of addition timing of superplasticizer (SP) on the fresh performance of PC, its impact on LC³, particularly in the context of 3DCP, remains less understood. This study assessed the effect of the SP addition time (either directly with the mixing water or with a 10-min delay) on the rheology and printing-related properties of LC³ and PC. Rotational rheometry and 3DP-related tests were conducted over two hours, besides hydration assessment through thermogravimetric analysis (TGA). The results showed that adding SP directly to LC³ led to significantly higher yield stress (1.2–2.5 times) and viscosity (14–59 % higher) values compared to delayed SP addition within the same time frame. However, LC³ exhibited slower rates of yield stress and viscosity increase over time in contrast to PC (with Athix structuration rate approximately 92 % lower for LC³). These tendencies influenced printability performance. While direct SP addition reduced PC's open time from 100 to 30 min, it had no impact on LC³ 's open time, which remained at 80 min. TGA analysis yielded additional insights, highlighting that hydrating LC³ samples required a greater free water content to achieve the same yield stress as PC and this difference was attributed to the presence of calcined clay. These findings make contributions to the technical and scientific communities by enhancing comprehension of LC³ cement fresh behavior and solidifying 3DCP as a disruptive construction method.
Rheology and pumpability of mix suitable for extrusion-based concrete 3D printing – A review
2023, Construction and Building Materials
3D printing of concrete is a rapidly growing additive manufacturing technology, bringing advantages like freedom of geometry, formwork-free construction, reduced construction time, and wastage, contributing towards a sustainable built environment. The technology also has the potential to mimic bio-inspired material architectures with enhanced performance. Among the available additive manufacturing techniques, the scalability and the speed of construction motivate the adaptation of extrusion-based concrete 3D printing technology. For conventional concrete pumping, the rheological behaviour and the mix design have been well established. However, for 3D printing, the pumpability of the mix which is governed by its rheology and the flow mechanism has to be viewed in conjunction with the extrudability, shape-retention, and buildability. This study provides a review of significant rheological properties, the effect of various material mixes, and printer configurations on the pumping of conventional as well as printable concrete, and a general comparison between them. The requirements of a pumpable concrete mix based on rheology and the optimal hardened properties for the 3D printing application are discussed. The significant rheological properties affecting the printability of concrete are plastic viscosity, static yield stress, thixotropy, and open time. A detailed review of various factors affecting the pumpability of a printable concrete mix is presented. The key constituents of a concrete mix affecting pumpability identified here are the type of binder(s), chemical admixture, the inclusion of nano-fillers, aggregate shape, size and grading, and aggregate-to-cement ratio. The range of yield stress and plastic viscosity are discussed for the 3D printable mixes. Recommendations are provided to improve the process and quality of 3D concrete printing. State-of-the-art applications and the potential of this technology to manufacture nature-inspired material architectures with superior toughness is highlighted.

View all citing articles on Scopus

View full text

Role of temperature in 3D printed geopolymers: Evaluating rheology and buildability

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Final considerations

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgments

J. Build. Eng.

Constr. Build. Mater.

J. Clean. Prod.

Constr. Build. Mater.

Constr. Build. Mater.